Insect morphology
Encyclopedia
The morphology
of insects enables the phenomenal success of this class
of arthropods. The sheer quantity and diversity of its taxa
are matched by a large variation of modifications in its body structure. The high rate of speciation
, short generations and long lineage have caused insects to evolve in many ways resulting in very large variations in morphology. These modifications allow insects to occupy almost every ecological niche
, utilise a staggering variety of food sources and possess diverse lifestyles. Insect body sizes range from 0.3 mm in the case of mymarid wasps which parasitise insect eggs to the 30 cms wingspan of the American owlet moth Thysania agrippina (family Noctuidae
).
Insects are by far the most successful group in the Arthropoda. They differ in significant ways from the other classes of Hexapoda
, such as Protura, Collembola and others) who are now considered by some authorities to be more basal
than insects.
ed bodies supported by an exoskeleton
, a hard jointed outer covering made mostly of chitin
. The segments of the body are organized into three distinctive but interconnected units, or tagmata
; a head, a thorax
, and an abdomen
. The head supports a pair of sensory antennae
, a pair of compound eyes, if present, one to three simple eyes or (ocelli) and three sets of variously modified appendages that form the mouthparts
. The thorax has six segmented legs
(one pair each for the prothorax, mesothorax and the metathorax segments making up the thorax) and two or four wings
(if present in the species). The abdomen (made up of eleven segments some of which may be reduced or fused) has most of the digestive
, respiratory
, excretory
and reproductive internal structures. There is considerable variation and many adaptations in the body parts of insects especially wings, legs, antenna, mouth-parts etc.
, is made up of two layers; the epicuticle which is a thin and waxy water resistant outer layer and contains no chitin, and another layer under it called the procuticle. This is chitinous and much thicker than the epicuticle and has two layers, the outer being the exocuticle while the inner is the endocuticle. The tough and flexible endocuticle is built from numerous layers of fibrous chitin and proteins, criss-crossing each others in a sandwich pattern, while the exocuticle is rigid and sclerotized. The exocuticle is greatly reduced in many soft-bodied insects, especially the larva
l stages (e.g., caterpillar
s). Chemically chitin is a long-chain polymer
of a N-acetylglucosamine
, a derivative of glucose. In its unmodified form, chitin is translucent, pliable, resilient and quite tough. In arthropod
s, however, it is often modified, becoming embedded in a hardened protein
aceous matrix, which forms much of the exoskeleton
. In its pure form it is leathery, but when encrusted in calcium carbonate
it becomes much harder. The difference between the unmodified and modified forms can be seen by comparing the body wall of a caterpillar
(unmodified) to a beetle
(modified).
From the embryonic stages itself, a layer of columnar or cuboidal epithelial cells give rise to the external cuticle and an internal basement membrane. The majority of insect material is held in the endocuticle. The cuticle provides muscular support and acts as a protective shield as the insect develops. However since it cannot grow the external sclerotised part of the cuticle is periodically shed in a process called "moulting". As the time for moulting approaches, most of the exocuticle material is reabsorbed. In moulting, first the old cuticle separates from the epidermis (apodysis). Enzymatic moulting fluid is released in between the old cuticle and epidermis which separates the exocuticle by digesting the endocuticle and sequestering its material for the new cuticle. When the new cuticle has formed sufficiently, the epicuticle and reduced exocuticle are shed in ecdysis
.
There are four principal regions of an insect body segment: tergum
or dorsal, sternum
or ventral and the two pleura or lateral. Hardened plates in the exoskeleton are called sclerites. Sclerites that are subdivisions of the major regions are tergites, sternites and pleurites, for the respective regions tergum, sternum and pleuron.
is enclosed in a hard, heavily sclerotized, unsegmented, exoskeletal head capsule, or epicranium
, which contains most of the sensing organs, including the antennae, ocellus or eyes, and the mouthparts. Out of all the insect orders, Orthoptera displays the most features found in other insects, including the sutures and sclerite
s. here, the vertex
, or the apex (dorsal region), is situated between the compound eyes for insects with a hypognathous and opisthognathous head. In prognathous insects, the vertex is not found between the compound eyes, but rather, where the ocelli
are normally. This is because the primary axis of the head is rotated 90 degrees to become parallel to the primary axis of the body. In some species this region is modified and assumes a different name.
The ecdysial suture is made of the coronal, frontal, epicranial sutures plus the ecdysial and cleavage lines; which is varies among different species of insects. The ecdysial suture is longitudinally placed on the vertex and separates the epicranial halves of the head to the left and right sides. Depending in the insect, the suture may come in different shapes: like either a Y, U, or V. those diverging lines that make up the ecdysial suture are called the frontal sutures or fontogenal sutures. Not all species of insect have frontal sutures, but in those who do, it helps the individual emerge from the integument when molting. The frons
is that part of the head that is ventrad, or towards the ventral and lower, of the vertex. the frons varies in size and is sometimes hard to identify, especially its borders in some species. However in most species, the frons is separated by the frontoclypeal or epistomal sutures; a transverse suture located under the antennae sockets.
The clypeus
is a sclerite between the face and labrum, which is dorsally separated from the frons by the frontoclypeal suture in primitive insects. The clypeogenal suture laterally democrates the clypeus, with the clypeus ventrally separated from the labrum by the clypeolabral suture. The clypeus differs in shape and size, such as species of Lepidoptera with a large clypeus with elongated mouthparts. The cheek or gena
forms the sclerotized area on each side of the head below the compound eyes extending to the gular suture. Like many of the other parts making up the insect's head, the gena varies among species with its boundaries difficult to establish. For example, in dragonflies and damselflies (Odonata
) is between the compound eyes, clypeus, and mouthparts. The postgena is the area immediately posteriad, or posterior or lower of the gena of pterygote insect
s and form the lateral and ventral parts of the occipital arch. The occipital arch is a narrow band forming the posterior edge of the head capsule arching dorsally over the foramen. The subgenal area is usually narrow, located above the mouthparts; this area also includes the hypostoma and pleurostoma
. The vertex extends anteriorly above the bases of the antennae as a prominent, pointed, concave rostrum. The posterior wall of the head capsule is penetrated by a large aperture, the foramen. Through it pass the organ systems, such as nerve cord
, esophagus
, salivary duct
s, and musculature, connecting the head with the thorax
.
Of the posterior aspect of the head, included are the occiput
, postgena, occipital formen, posterior tentorial pit, gula
, postgenal bridge, the hypostomal suture and bridge, and the mandibles, labium
, and maxilla
. The occiputal suture is well founded in species of Orthoptera, but not so much in other orders. Where found, the occipital suture is arched, horseshoe-shaped groove on the back of the head, ending at the posterior of each mandible. The postoccipital suture is a landmark on the posterior surface of the head and is typically near the occipital foremen. In pterygotes, the postocciput forms the extreme posterior, often U-shaped which forms the rim of the head extending to the postoccipital suture. In pterygotes, such as those of Orthoptera, the occipital foramen and the mouth are not separated. The three types of occipital closures, or points under the occipital foramen that separate the two lower halves of the postgena: the hypostomal bridge, postgenal bridge, and the gula. The hypstosaml bridge is usually found in insects with hypognathous orientation. The postgenal bridge is found in the adult species of higher Diptera
, and aculeate Hymenoptera
, while the gula is found on some Coleoptera, Neuroptera
,and Isoptera which typically display a prognathous orientated mouthparts.
, singular), of which there may be up to 30,000 ommatidia in a single compound eye. This type of eye gives less resolution than eyes found in vertebrates, but it gives acute perception of movement. There can also be an additional two or three ocelli, which help detect low light or small changes in light intensity. The image perceived is a combination of inputs from the numerous ommatidia, which are located on a convex surface, thus pointing in slightly different directions. Compared with simple eyes, compound eyes possess a very large view angle, and can detect fast movement and, in some cases, the polarization of light.
Because the individual lenses are so small, the effects of diffraction
impose a limit on the possible resolution that can be obtained (assuming that they do not function as phased array
s). This can only be countered by increasing lens size and number. To see with a resolution comparable to our simple eyes, humans would require compound eyes which would each reach the size of their head. Compound eyes fall into two groups: apposition eyes, which form multiple inverted images, and superposition eyes, which form a single erect image. Compound eyes grow at their margins by the addition of new ommatidia.
e function almost exclusively in sensory perception, some of the sensory uses of antennae include motion and orientation, odor, sound, humidity, and a variety of chemical cues. Antennae vary greatly among insects, but all follow a basic plan, of which include the first and second segments are termed the scape and pedicel, respectively. The remaining antennal segments or flagellomeres are jointly called the flagellum
. There are many different types of antennae among different species, including setaceous, moniliform, serrate, pectinate, clavate, lamellate, geniculate, and plumose.
The mouthparts, along with the rest of the head, can be articulated in at least three different positions: prognathous, opisthognathous and hypognathous. In species with prognathous articulation, the head is positioned vertically aligned with the body, such as species of Formicidae; while in a hypognathous type, the head is aligned horizontally adjacent to the body. In a opisthognathous head, it was positioned diagonally, such as species of Blattodea and some Coleopterans. The mouthparts very greatly among insects of different orders but there are two main functional groups: mandibulate and haustellate. Haustellate mouthparts are those used for sucking liquids and can be further classified, by the presence of stylet
s, which include: piercing-sucking, sponging, and siphoning. The stylets are needle-like projections used to penetrate plant and animal tissue. The stylets and the feeding tube form the modified mandibles, maxilla, and hypopharynx.
Mouthparts that are mandibular are found in species of Odonata
, Isoptera, adult Neuroptera
, Coleoptera, Hymenoptera
, Blattaria, Orthoptera
, and Lepidoptera
. However most adult Lepidoptera have siphoning mouthparts, while the larvae (commonly called caterpillar
s) are the ones with the mandibles.
The labrum
is a broad lobe forming the roof of the preoral cavity, suspended from the clypeus in front of the mouth and forming the upper lip. On its inner side it is membranous and may be produced into a median lobe, the epipharynx, bearing some sensilla
. The labrum is raised away from the mandibles by two muscles arising in the head and inserted medially into the anterior margin of the labrum. It is closed against the mandibles in part by two muscles arising in the head and inserted on the posterior lateral margins on two small sclerites, the tormae, and, at least in some insects, by a resilin spring in the cuticle at the junction of the labrum with the clypeus. Differential use of the muscles. Until recently, the labrum generally was considered to be associated with first head segment. However recent studies of the embryology, gene expression, and nerve supply to the labrum show that it is innervated by the tritocerebrum of the brain, which is the fused ganglia of the third head segment. This is formed from fusion of parts of a pair of ancestral appendages found on the third head segment, showing their relation. Its ventral, or inner, surface is usually membranous and forms the lobe-like epipharynx, which bears mechanosensilla and chemosensilla.
Chewing insects have two mandibles, one on each side of the head. The mandibles are positioned between the labrum and maxillae. The mandibles cut and crush food and may be used for defense; generally they have an apical cutting edge and the more basal molar area grinds the food. They can be extremely hard (approximately 3 on Moh’s scale of mineral hardness
, or an indentation hardness of about 30 kg mm−2) and thus many termites and beetles have no physical difficulty in boring through foils made from such common metals as copper, lead, tin, and zinc. The cutting edges are typically strengthened by the addition of zinc, manganese or, rarely, iron, in amounts up to about 4% of the dry weight. They are typically the largest mouthparts of chewing insects, being used to masticate (cut, tear, crush, chew) food items. They open outwards (to the sides of the head) and come together medially. In carnivorous chewing insects, the mandibles can be modified to be more knife-like, whereas in herbivorous chewing insects, they are more typically broad and flat on their opposing faces (e.g., caterpillar
s). In male stag beetle
s, the mandibles are modified to such an extent that they do not serve any feeding function, but are instead used to defend mating sites from other males. In ant
s, the mandibles also serve a defensive function (particularly in soldier castes). In bull ants
, the mandibles are elongate and toothed, used as hunting (and defensive) appendages.
Situated beneath the mandibles, paired maxilla
e manipulate food during mastication
. Maxillae can have hairs and "teeth" along their inner margins. At the outer margin, the galea
is a cupped or scoop-like structure, which sits over the outer edge of the labium. They also have palps, which are used to sense the characteristics of potential foods. The maxillae occupy a lateral position, one on each side of the head behind the mandibles. The proximal part of the maxilla consists of a basal cardo, which has a single articulation with the head, and a flat plate, the stipes, hinged to the cardo
. Both cardo and stipes are loosely joined to the head by membrane so that they are capable of movement. Distally on the stipes are two lobes, an inner lacinea and an outer galea, one or both of which may be absent. More laterally on the stipes is a jointed, leglike palp made up of a number of segments; in Orthoptera there are five. Anterior and posterior rotator muscles are inserted on the cardo, and ventral adductor muscles arising on the tentorium are inserted on both cardo and stipes. Arising in the stipes are flexor muscles of lacinea and galea and another lacineal flexor arises in the cranium, but neither lacinea nor galea has an extensor muscle. The palp has levator and depressor muscles arising in the stipes and each segment of the palp has a single muscle causing flexing of the next segment.
In mandibulate mouthparts, the labium
is a quadrupedal structure, although it is formed from two fused secondary maxillae. It can be described as the floor of the mouth. With the maxillae, it assists manipulation of food during mastication
or chewing or, in the unusual case of the dragonfly nymph, extends out to snatch prey back to the head where mandibles can eat it. The labium is similar in structure to the maxilla
e, but with the appendages of the two sides fused by the midline, so that they come to form a median plate. The basal part of the labium, equivalent to the maxillary cardines and possibly including a part of the sternum of the labial segment, is called the postmentum. This may be subdivided into a proximal submentum and a distal mentum. Distal to the postmentum, and equivalent to the fused maxillary stipites, is the prementum. The prementum closes the pre-oral cavity from behind. Terminally it bears four lobes, two inner glossae and two outer paraglossae, which are collectively known as the ligula. One or both pairs of lobes may be absent or they may be fused to form a single median process. A palp arises from each side of the prementum, often being three segmented.
The hypopharynx is a median lobe immediately behind the mouth, projecting forwards from the back of the preoral cavity, is a lobe of uncertain origin, but perhaps associated with the mandibular segment; in apterygotes, earwigs, and nymphal mayflies the hypopharynx bears a pair of lateral lobes, the superlinguae (singular: superlingua). It divides the cavity into a dorsal food pouch, or cibarium, and a ventral salivarium into which the salivary duct opens. Though, it is commonly found fused to the libium. Most of the hypopharynx is membranous, but the adoral face is sclerotized distally, and proximally contains a pair of suspensory sclerites which extend upwards to end in the lateral wall of the stomodeum. Muscles arising on the frons are inserted into these sclerites, which distally are hinged to a pair of lingual sclerites. These, in turn, have inserted into them antagonistic pairs of muscles arising on the tentorium and labium. The various muscles serve to swing the hypopharynx forwards and back, and in the cockroach there are two more muscles running across the hypopharynx which dilate the salivary orifice and expand the salivarium.
Some mouthparts have adapted special piercing parts along with the already sponging ones, used to pierce through tissues of plants and animals. Mosquitoes are infamous for being hemophagous (feeding on blood) pest of people as the female pierces the skin (which could spread disease). The parts of mosquito proboscis are the paired mandibles and maxillae that form needle-like structures, called stylet
s, which are enclosed by the labium. When mosquito bites, maxillae penetrate the skin and anchor the mouthparts thus allowing other parts to be inserted. The sheath-like labium slides back and the remaining mouthparts pass through its tip and into the tissue. Then through hypopharynx mosquito injects saliva
, which contains anticoagulants that stop the blood from clotting. And finally the labrum (upper lip) is used to suck up the blood. Species of the genus Anopheles are characterized by their long palpi (two parts with widening end), almost reaching the end of labrum.
The proboscis
(plural – probosces) is formed from maxillary galeae and is adaption found in some insects for sucking. The muscles of the cibarium or pharynx are strongly developed which form the pump. In Hemiptera and many Diptera, which feed on fluids within plants or animals, some components of the mouthparts are modified for piercing, and the elongate structures are called stylets. The combined tubular structures are referred to as the proboscis, although specialized terminology is used in some groups.
In species of Lepidoptera
(i.e. Butterflies and moths), it consists of two tubes held together by hooks and separable for cleaning. Each tube is inwardly concave, thus forming a central tube up which moisture is sucked. Suction is effected through the contraction and expansion of a sac in the head. The proboscis is coiled under the head when the insect is at rest and extended only when feeding. The maxillary palpi are reduced and even vestigial. They are conspicuous and 5-segmented in some of the more basal families and are often folded. The shape and dimensions of the proboscis have evolved to give different species a wider and therefore more advantageous diet. There is an allometric scaling relationship between body mass of Lepidoptera and length of proboscis from which an interesting adaptive departure is the unusually long-tongued hawk moth Xanthopan morgani praedicta
. Charles Darwin
predicted the existence and proboscis length of this moth before its discovery based on his knowledge of the long-spurred Madagascan star orchid Angraecum sesquipedale
.
The mouthparts of insects which feed on fluids are modified in various ways to form a tube through which liquid can be drawn into the mouth and usually another through which saliva passes. The muscles of the cibarium or pharynx are strongly developed to form a pump. In non-biting flies the mandibles are absent and other structures are reduced; the labial palps have become modified to form the labellum and the maxillary palps are present, although sometimes short. In Brachycera, the labellum is especially prominent and used for sponging liquid or semi-liquid food. The labella is a complex structure consisting of many grooves, called pseudotrachea, which sops up liquids. Salivary secretions from the labella assist in dissolving and collecting food particles so that they may be more easily taken up by the pseudotrachea, this is thought to occur by capillary action. The liquid food is then drawn up from the pseudotracheae through the food channel into the esophagus
.
The mouthparts of bee
s are of a chewing and lapping-sucking type. Lapping is a mode of feeding in which liquid or semi-liquid food adhering to a protrusible organ, or “tongue”, is transferred from substrate to mouth. In the honey bee
(Hymenoptera
: Apidae
: Apis mellifera), the elongate and fused labial glossae form a hairy tongue, which is surrounded by the maxillary galeae and the labial palps to form a tubular proboscis containing a food canal. In feeding, the tongue is dipped into the nectar or honey, which adheres to the hairs, and then is retracted so that adhering liquid is carried into the space between the galeae and labial palps. This back-and-forth glossal movement occurs repeatedly. Movement of liquid to the mouth apparently results from the action of the cibarial pump, facilitated by each retraction of the tongue pushing liquid up the food canal.
, mesothorax
, and the metathorax
. The anterior segment, closest to the head, is the prothorax, with the major features being the first pair of legs and the pronotum. The middle segment is the mesothorax with the major features being the second pair of legs and the anterior wings. The third and most posterior segment, abutting the abdomen, is the metathorax, which features the third pair of legs and the posterior wings. Each segment is dilineated by an intersegmental suture. Each segment has four basic regions. The dorsal surface is called the tergum (or notum) to distinguish them from the abdominal terga. The two lateral regions are called the pleura (singular: pleuron) and the ventral aspect is called the sternum. In turn, the notum of the prothorax is called the pronotum, the notum for the mesothorax is called the mesonotum and the notum for the metathorax is called the metanotum. Continuing with this logic, there is also the mesopleura and metapleura as well as the mesosternum and metasternum.
The tergal plates of the thorax are simple structures in apterygotes and in many immature insects, but are variously modified in winged adults. The pterothoracic nota each have two main divisions: the anterior wing-bearing alinotum and the posterior phragma-bearing postnotum. Phragmata (singular: phragma) are plate-like apodemes that extend inwards below the antecostal sutures, marking the primary intersegmental folds between segments; phragmata provide attachment for the longitudinal flight muscles. Each alinotum (sometimes confusingly referred to as a “notum”) may be traversed by sutures that mark the position of internal strengthening ridges and commonly divide the plate into three areas: the anterior prescutum, the scutum, and the smaller posterior scutellum. The lateral pleural sclerites are believed to be derived from the subcoxal segment of the ancestral insect leg. These sclerites may be separate, as in silverfish, or fused into an almost continuous sclerotic area, as in most winged insects.
and elytra in Coleoptera), arise between the mesonotum and the mesopleura, and the hindwings articulate between the metanotum and metapleura. The mesopleura and metapleura are where the legs arise from. The mesothorax and metathorax each have a pleural suture (mesopleural and metapleural sutures) that runs from the wing base to the coxa of the leg. The sclerite anterior to the pleural suture is called the episternum (serially, the mesepisternum and metepisternum). The sclerite posterior to the suture is called the epimiron (serially, the mesepimiron and metepimiron). Spiracles, the external organs of the respiratory system, are found on the pterothorax, usually one between the pro- and mesopleoron as well as one between the meso- and metapleuron.
The ventral view or sternum follows the same convention, with the prosternum under the prothorax, the mesosternum under the mesothorax and the metasternum under the metathorax. The notum, pleura and sternum of each segment have a variety of different sclerites and sutures which vary greatly from order to order, and they will not be discussed in detail in this section.
located on the second and third thoracic segments. Insects are the only invertebrate
s to have developed flight capability, and this has played an important part in their success. Insect flight
is not very well understood, relying heavily on turbulent aerodynamic effects. The primitive insect groups use muscles that act directly on the wing structure. The more advanced groups making up the Neoptera
have foldable wings and their muscles act on the thorax wall and power the wings indirectly. These muscles are able to contract multiple times for each single nerve impulse, allowing the wings to beat faster than would ordinarily be possible.
Insect flight can be extremely fast, maneuverable and versatile. This flight is possible due to the changing shape, extraordinary control and variable motion of the insect wing. Insect orders use different flight mechanisms, for example, the flight of a butterfly can be explained using steady-state, non-transitory aerodynamics
and thin aerofoil
theory. For a more detailed description, see insect flight
.
Each of the wings consists of a thin membrane supported by a system of veins. The membrane is formed by two layers of integument closely apposed, while the veins are formed where the two layers remain separate and the cuticle may be thicker and more heavily sclerotized. Within each of the major veins is a nerve and a trachea, and, since the cavities of the veins are connected with the hemocoel, hemolymph can flow into the wings. Also are the wings lumen, being an extension of the hemocoel, which contains the tracheae, nerves, and hemolymph. As the wing develops, the dorsal and ventral integumental layers become closely apposed over most of their area forming the wing membrane. The remaining areas form channels, the future veins, in which the nerves and tracheae may occur. The cuticle surrounding the veins becomes thickened and more heavily sclerotized to provide strength and rigidity to the wing. Hairs of two types may occur on the wings: microtrichia, which are small and irregularly scattered, and macrotrichia, which are larger, socketed, and may be restricted to veins. The scales of Lepidoptera and Trichoptera are highly modified macrotrichia.
In some very small insects, the venation may be greatly reduced. In Chalcidoidea (Chalcid wasps), for instance, only the subcosta and part of the radius are present. Conversely, an increase in venation may occur by the branching of existing veins to produce accessory veins or by the development of additional, intercalary veins between the original ones, as in the wings of Orthoptera
(Grasshoppers and crickets). Large numbers of cross-veins are present in some insects, and they may form a reticulum as in the wings of Odonata
(Dragonflies and damselflies) and at the base of the forewings of Tettigonioidea and Acridoidea
(Katydids and grasshoppers respectively).
The archedictyon is the name given to a hypothetical scheme of wing venation proposed for the very first winged insect. It is based on a combination of speculation and fossil data. Since all winged insects are believed to have evolved from a common ancestor, the archediction represents the "template" that has been modified (and streamlined) by natural selection for 200 million years. According to current dogma, the archedictyon contained 6-8 longitudinal veins. These veins (and their branches) are named according to a system devised by John Comstock and George Needham—the Comstock-Needham System:
The costa (C) is the leading marginal vein on most insects, although sometimes there is a small vein above the cost called the precosta, although in almost all extant insects, the precosta is fused with the costa; The costa rarely ever branch because is at the leading edge, which is associated at its base with the humeral plate. The trachea of the costal vein is perhaps a branch of the subcostal trachea. Located after the costa is the third vein, the subcosta, which branches into two two separate veins: the anterior and posterior. The base of the subcosta is associated with the distal end of the neck of the first axillary (see section below). The fourth vein is the radius (R), which is branched into five separate veins. The radius is generally the strongest vein of the wing. Toward the middle of the wing it forks into a first undivided branch (R1) and a second branch, called the radial sector (Ra), which subdivides dichotomously into four distal branches (R2, R3, R4, R5). Basally the radius is flexibly united with the anterior end of the second axillary (2Ax).
The fifth vein of the wing is the media. In the archetype pattern (A) the media forks into two main branches, a media anterior (MA), which divides into two distal branches (MA1, MA2), and a median sector, or media posterior (MP), which has four terminal branches (M1, M2, M3, M4). In most modern insects the media anterior has been lost, and the usual "media" is the four-branched media posterior with the common basal stem. In the Ephemerida, according to present interpretations of the wing venation, both branches of the media are retained, while in Odonata the persisting media is the primitive anterior branch. The stem of the media is often united with the radius, but when it occurs as a distinct vein its base is associated with the distal median plate (m') or is continuously sclerotized with the latter. The cubitus, the sixth vein of the wing, is primarily two branched. The primary forking of the takes place near the base of the wing, forming the two principal branches (Cu1, Cu2). The anterior branch may break up into a number of secondary branches, but commonly it forks into two distal branches. The second branch of the cubitus (Cu2) in Hymenoptera, Trichoptera, and Lepidoptera was mistaken by Comstock and Needham for the first anal. Proximally the main stem of the cubitus is associated with the distal median plate (m') of the wing base.
Postcubitus (Pcu) is the first anal of the Comstock and Needham system. The Postcubitus, however, has the status of an independent wing vein and should be recognized as such. In nymphal wings, its trachea arises between the cubital trachea and the group of vannal tracheae. In the mature wings of more generalized insect the Postcubitus is always associated proximally with the cubitus and is never intimately connected with the flexor sclerite (3Ax) of the wing base. In Neuroptera, Mecoptera, and Trichoptera the postcubitus may be more closely associated with the vannal veins, but its base is always free from the latter. The postcubitus is usually unbranched; it is primitively two branched. The vannal veins (lV to nV) are the anal veins that are immediately associated with the third axillary, and which are directly affected by the movement of this sclerite that brings about the flexion of the wings. In number the vannal veins vary. from 1 to 12, according to the expansion of the vannal area of the wing. The vannal tracheae usually arise from a common tracheal stem in nymphal insects, and the veins are regarded as branches of a single anal vein. Distally the vannal veins are either simple or branched. Jugal Veins (J) of the jugal lobe of the wing is often occupied by a network of irregular veins, or it may be entirely membranous; but sometimes it contains one or two distinct small veins, the first jugal vein, or vena arcuata, and the second jugal vein, or vena cardinalis (2J).
All the veins of the wing are subject to secondary forking and to union by cross-veins. In some orders of insects the cross-veins are so numerous that the whole venational pattern becomes a close network of branching veins and cross-veins. Ordinarily, however, there is a definite number of cross-veins having specific locations. The more constant cross-veins are the humeral cross-vein (h) between costa and subcosta, the radial cross-vein (r) between R and the first fork of Rs, the sectorial cross-vein (s) between the two forks of R8, the median cross-vein (m-m) between M2 and M3, and the mediocubital cross-vein (m-cu) between media and cubitus.
The veins of insect wings are characterized by a convex-concave placement, such as those seen in mayflies (i.e., concave is "down" and convex is "up") which alternate regularly and by their branching; whenever a vein forks there is always an interpolated vein of the opposite position between the two branches. The a concave vein will fork into two concave veins (with the interpolated vein being convex) and the regular alteration of the veins is preserved. The veins of the wing appear to fall into an undulating according to whether they have a tendency to fold up or down when the wing is relaxed. The basal shafts of the veins are convex, but each vein forks distally into an anterior convex branch and a posterior concave branch. Thus the costa and subcosta are regarded as convex and concave branches of a primary first vein, Rs is the concave branch of the radius, posterior media the concave branch of the media, Cu1 and Cu2 are respectively convex and concave, while the primitive Postcubitus and the first vannal have each an anterior convex branch and a posterior concave branch. The convex or concave nature of the veins has been used as evidence in determining the identities of the persisting distal branches of the veins of modern insects, but it has not been demonstrated to be consistent for all wings.
Wing areas are delimited and subdivided by fold-lines, along which the wings can fold. Along with the flexion-lines, at which flexes during flight. Between the flexion-lines and the fold-lines, the fundamental distinction is often blurred, as fold-lines may permit some flexibility or vice-versa. Two constants that are found in nearly all insect wings are the claval (a flexion-line) and jugal folds (or fold line); forming variable and unsatisfactory boundaries. Wing foldings can very complicated, with transverse folding occurs in the hind wings of Dermaptera and Coleoptera, and in some insects the anal area can be folded like a fan.
There are about four different fields found on the insect wings:
Most veins and crossveins occur in the anterior area of the remigium, which is responsible for most of the flight, powered by the thoracic muscles. The posterior portion of the remigium is sometimes called the clavus; the two other posterior fields are the anal and jugal areas. When the vannal fold has the usual position anterior to the group of anal veins, the remigium contains the costal, subcostal, radial, medial, cubital, and postcubital veins. In the flexed wing the remigium turns posteriorly on the flexible basal connection of the radius with the second axillary, and the base of the mediocubital field is folded medially on the axillary region along the plica basalis (bf) between the median plates (m, m') of the wing base.
The vannus is bordered by the vannal fold, which typically occurs between the postcubitus and the first vannal vein. In Orthoptera it usually has this position. In the forewing of Blattidae, however, the only fold in this part of the wing lies immediately before the postcubitus. In Plecoptera the vannal fold is posterior to the postcubitus, but proximally it crosses the base of the first vannal vein. In the cicada the vannal fold lies immediately behind the first vannal vein (lV). These small variations in the actual position of the vannal fold, however, do not affect the unity of action of the vannal veins, controlled by the flexor sclerite (3Ax), in the flexion of the wing. In the hind wings of most Orthoptera a secondary vena dividens forms a rib in the vannal fold. The vannus is usually triangular in shape, and its veins typically spread out from the third axillary like the ribs of a fan. Some of the vannal veins may be branched, and secondary veins may alternate with the primary veins. The vannal region is usually best developed in the hind wing, in which it may be enlarged to form a sustaining surface, as in Plecoptera and Orthoptera. The great fanlike expansions of the hind wings of Acrididae are clearly the vannal regions, since their veins are all supported on the third axillary sclerites on the wing bases, though Martynov (1925) ascribes most of the fan areas in Acrididae to the jugal regions of the wings. The true jugum of the acridid wing is represented only by the small membrane (Ju) mesad of the last vannal vein. The jugum is more highly developed in some other Orthoptera, as in the Mantidae. In most of the higher insects with narrow wings the vannus becomes reduced, and the vannal fold is lost, but even in such cases the flexed wing may bend along a line between the postcubitus and the first vannal vein.
The Jugal Region, or Neala, is a region of the wing that is usually a small membranous area proximal to the base of the vannus strengthened by a few small, irregular veinlike thickenings; but when well developed it is a distinct section of the wing and may contain one or two jugal veins. When the jugal area of the forewing is developed as a free lobe, it projects beneath the humeral angle of the hind wing and thus serves to yoke the two wings together. In the Jugatae group of Lepidoptera it bears a long finger-like lobe. The jugal region was termed the neala ("new wing") because it is evidently a secondary and recently developed part of the wing.
The axilary region is region containing the axillary sclerites has in general the form of a scalene triangle. The base of the triangle (a-b) is the hinge of the wing with the body; the apex (c) is the distal end of the third axillary sclerite; the longer side is anterior to the apex. The point d on the anterior side of the triangle marks the articulation of the radial vein with the second axillary sclerite. The line between d and c is the plica basalis (bf), or fold of the wing at the base of the mediocubital field.
At the posterior angle of the wing base in some Diptera there is a pair of membranous lobes (squamae, or calypteres) known as the alula. The alula is well developed in the house fly. The outer squama (c) arises from the wing base behind the third axillary sclerite (3Ax) and evidently represents the jugal lobe of other insects (A, D); the larger inner squama (d) arises from the posterior scutellar margin of the tergum of the wing-bearing segment and forms a protective, hoodlike canopy over the halter. In the flexed wing the outer squama of the alula is turned upside down above the inner squama, the latter not being affected by the movement of the wing. In many Diptera a deep incision of the anal area of the wing membrane behind the single vannal vein sets off a proximal alar lobe distal to the outer squama of the alula.
The various movements of the wings, especially in insects that flex the wings horizontally over the back when at rest, of which demand a more complicated articular structure at the wing base than a mere hinge of the wing with the body. Each wing is attached to the body by a membranous basal area, but the articular membrane contains a number of small articular sclerites, collectively known as the pteralia. The pteralia include an anterior humeral plate at the base of the costal vein, a group of axillaries (Ax) associated with the subcostal, radial, and vannal veins, and two less definite median plates (m, m') at the base of the mediocubital area. The axillaries are specifically developed only in the wing-flexing insects, where they constitute the flexor mechanism of the wing operated by the flexor muscle arising on the pleuron. Characteristic of the wing base is also a small lobe on the anterior margin of the articular area proximal to the humeral plate, which, in the forewing of some insects, is developed into a large, flat, scale-like flap, the tegula, overlapping the base of the wing. Posteriorly the articular membrane often forms an ample lobe between the wing and the body, and its margin is generally thickened and corrugated, giving the appearance of a ligament, the so-called axillary cord, continuous mesally with the posterior marginal scutellar fold of the tergal plate bearing the wing.
The articular sclerites, or pteralia, of the wing base of the wing-flexing insects and their relations to the body and the wing veins, shown diagrammatically, are as follows:
The humeral plate is usually a small sclerite on the anterior margin of the wing base, movable and articulated with the base of the costal vein. Odonata have their humeral plate grately enlargened, with two muscles arising from the episternum inserted into the Humeral plates and two from the edge of the epimeron inserted into the axillary plate.
The first axillary sclerite (lAx) is the anterior hinge plate of the wing base. Its anterior part is supported on the anterior notal wing process of the tergum (ANP); its posterior part articulates with the tergal margin. The anterior end of the sclerite is generally produced as a slender arm, the apex of which (e) is always associated with the base of the subcostal vein (Sc), though it is not united with the latter. The body of the sclerite articulates laterally with the second axillary. The second axillary sclerite (2Ax) is more variable in form than the first axillary, but its mechanical relations are no less definite. It is obliquely hinged to the outer margin of the body of the first axillary, and the radial vein (R) is always flexibly attached to its anterior end (d). The second axillary presents both a dorsal and a ventral sclerotization in the wing base; its ventral surface rests upon the fulcral wing process of the pleuron. The second axillary, therefore, is the pivotal sclerite of the wing base, and it specifically manipulates the radial vein.
The third axillary sclerite (3Ax) lies in the posterior part of the articular region of the wing. Its form is highly variable and often irregular, but the third axillary is the sclerite on which is inserted the flexor muscle of the wing (D). Mesally it articulates anteriorly (f) with the posterior end of the second axillary, and posteriorly (b) with the posterior wing process of the tergum (PNP), or with a small fourth axillary when the latter is present. Distally the third axillary is prolonged in a process which is always associated with the bases of the group of veins in the anal region of the wing here termed the vannal veins (V). The third axillary, therefore, is usually the posterior hinge plate of the wing base and is the active sclerite of the flexor mechanism, which directly manipulates the vannal veins. The contraction of the flexor muscle (D) revolves the third axillary on its mesal articulations (b, f) and thereby lifts its distal arm; this movement produces the flexion of the wing. The Fourth Axillary sclerite is not a constant element of the wing base. When present it is usually a small plate intervening between the third axillary and the posterior notal wing process and is probably a detached piece of the latter.
The median plates (m, m' are also sclerites that are not so definitely differentiated as specific plates as are the three principal axillaries, but nevertheless they are important elements of the flexor apparatus. They lie in the median area of the wing base distal to the second and third axillaries and are separated from each other by an oblique line (bf) which forms a prominent convex fold during flexion of the wing. The proximal plate (m) is usually attached to the distal arm of the third axillary and perhaps should be regarded as a part of the latter. The distal plate ( m') is less constantly present as a distinct sclerite and may be represented by a general sclerotization of the base of the mediocubital field of the wing. When the veins of this region are distinct at their bases, they are associated with the outer median plate.
In many insect species, the fore and hind wing are coupled together, which improves the aerodynamic efficiency of flight. The most common coupling mechanism (e.g., Hymenoptera
and Trichoptera
) is a row of small hooks on the forward margin of the hind wing, or "hamuli", which lock onto the fore wing, keeping them held together (hamulate coupling). In some other insect species (e.g., Mecoptera
, Lepidoptera
, and some Trichoptera
) the jugal lobe of the fore wing covers a portion of the hind wing (jugal coupling), or the margins of the fore and hind wing overlap broadly (amplexiform coupling), or the hindwing bristles, or frenulum, hook under the retaining structure or retinalucum on the forewing.
When at rest, the wings are held over the back in most insects, which may involve longitudinal folding of the wing membrane and sometimes also transverse folding. Folding may sometimes occur along the flexion lines. Though fold lines may be transverse, as in the hind wings of beetles and earwigs, they are normally radial to the base of the wing, allowing adjacent sections of a wing to be folded over or under each other. The commonest fold line is the jugal fold, situated just behind the third anal vein, although, most Neoptera have a jugal fold just behind vein 3A on the forewings. It is sometimes also present on the hindwings. Where the anal area of the hindwing is large, as in Orthoptera and Blattodea, the whole of this part may be folded under the anterior part of the wing along a vannal fold a little posterior to the claval furrow. In addition, in Orthoptera and Blattodea, the anal area is folded like a fan along the veins, the anal veins being convex, at the crests of the folds, and the accessory veins concave. Whereas the claval furrow and jugal fold are probably homologous in different species, the vannal fold varies in position in different taxa. Folding is produced by a muscle arising on the pleuron and inserted into the third axillary sclerite in such a waythat, when it contracts, the sclerite pivots about its points of articulation with the posterior notal process and the second axillary sclerite.
As a result, the distal arm of the third axillary sclerite rotates upwards and inwards, so that finally its position is completely reversed. The anal veins are articulated with this sclerite in such a way that when it moves they are carried with it and become flexed over the back of the insect. Activity of the same muscle in flight affects the power output of the wing and so it is also important in flight control. In orthopteroid insects, the elasticity of the cuticle causes the vannal area of the wing to fold along the veins. Consequently energy is expended in unfolding this region when the wings are moved to the flight position. In general, wing extension probably results from the contraction of muscles attached to the basalar sclerite or, in some insects, to the subalar sclerite.
, one trochanter, the femur
, the tibia
, the tarsus
, and the pretarsus. The coxa in its more symmetrical form, has the shape of a short cylinder or truncate cone, though commonly it is ovate and may be almost spherical. The proximal end of the coxa is girdled by a submarginal basicostal suture which forms internally a ridge, or basicosta, and sets off a marginal flange, the coxomarginale, or basicoxite. The basicosta strengthens the base of the coxa and is commonly enlarged on the outer wall to give insertion to muscles ; on the mesal half of the coxa, however, it is usually weak and often confluent with the coxal margin. The trochanteral muscles that take their origin in the coxa are always attached distal to the basicosta. The coxa is attached to the body by an articular membrane, the coxal corium, which surrounds its base. These two articulations are perhaps the primary dorsal and ventral articular points of the subcoxo-coxal hinge. In addition, the insect coxa has often an anterior articulation with the anterior, ventral end of the trochantin, but the trochantinal articulation does not coexist with a sternal articulation. The pleural articular surface of the coxa is borne on a mesal inflection of the coxal wall. If the coxa is movable on the pleural articulation alone, the coxal articular surface is usually inflected to a sufficient depth to give a leverage to the abductor muscles inserted on the outer rim of the coxal base. Distally the coxa bears an anterior and a posterior articulation with the trochanter. The outer wall of the coxa is often marked by a suture extending from the base to the anterior trochanteral articulation. In some insects the coxal suture falls in line with the pleural suture, and in such cases the coxa appears to be divided into two parts corresponding to the episternum and epimeron of the pleuron. The coxal suture is absent in many insects.
The inflection of the coxal wall bearing the pleural articular surface divides the lateral wall of the basicoxite into a prearticular part and a postarticular part, and the two areas often appear as two marginal lobes on the base of the coxa. The posterior lobe is usually the larger and is termed the meron
. The meron may be greatly enlarged by an extension distally in the posterior wall of the coxa; in the Neuroptera, Mecoptera, Trichoptera, and Lepidoptera, the meron is so large that the coxa appears to be divided into an anterior piece, the so-called "coxa genuina," and the meron, but the meron never includes the region of the posterior trochanteral articulation, and the groove delimiting it is always a part of the basicostal suture. A coxa with an enlarged meron has an appearance similar to one divided by a coxal suture falling in line with the pleural suture, but the two conditions are fundamentally quite different and should not be confused. The meron reaches the extreme of its departure from the usual condition in the Diptera. In some of the more generalized flies, as in the Tipulidae, the meron of the middle leg appears as a large lobe of the coxa projecting upward and posteriorly from the coxal base; in higher members of the order it becomes completely separated from the coxa and forms a plate of the lateral wall of the mesothorax.
The trochanter is the basal segment of the telopodite; it is always a small segment in the insect leg, freely movable by a horizontal hinge on the coxa, but more or less fixed to the base of the femur. When movable on the femur the trochantero femoral hinge is usually vertical or oblique in a vertical plane, giving a slight movement of production and reduction at the joint, though only a reductor muscle is present. In the Odonata, both nymphs and adults, there are two trochanteral segments, but they are not movable on each other; the second contains the reductor muscle of the femur. The usual single trochanteral segment of insects, therefore, probably represents the two trochanters of other arthropods fused into one apparent segment, since it is not likely that the primary coxotrochanteral hinge has been lost from the leg. In some of the Hymenoptera a basal subdivision of the femur simulates a second trochanter, but the insertion of the reductor muscle on its base attests that it belongs to the femoral segment, since as shown in the odonate leg, the reductor has its origin in the true second trochanter.
The femur
is the third segment of the insect leg, is usually the longest and strongest part of the limb, but it varies in size from the huge hind femur of leaping Orthoptera to a very small segment such as is present in many larval forms. The volume of the femur is generally correlated with the size of the tibial muscles contained within it, but it is sometimes enlarged and modified in shape for other purposes than that of accommodating the tibial muscles. The tibia
is characteristically a slender segment in adult insects, only a little shorter than the femur or the combined femur and trochanter. Its proximal end forms a more or less distinct head bent toward the femur, a device allowing the tibia to be flexed close against the under surface of the femur.
The tarsus
of insects corresponds to the penultimate segment of a generalized arthropod limb, which is the segment called the propodite in Crustacea. adult insects it is commonly subdivided into from two to five subsegments, or tarsomeres, but in the Protura, some Collembola, and most holometabolous insect larvae it preserves the primitive form of a simple segment. The subsegments of the adult insect tarsus are usually freely movable on one another by inflected connecting membranes, but the tarsus never has intrinsic muscles. The tarsus of adult pterygote insects having fewer than five subsegments is probably specialized by the loss of one or more subsegments or by a fusion of adjoining subsegments. In the tarsi of Acrididae the long basal piece is evidently composed of three united tarsomeres, leaving the fourth and the fifth. The basal tarsomere is sometimes conspicuously enlarged and is distinguished as the basitarsus. On the under surfaces of the tarsal subsegments in certain Orthoptera there are small pads, the tarsal pulvilli, or euplantulae. The tarsus is occasionally fused with the tibia in larval insects, forming a tibiotarsal segment; in some cases it appears to be eliminated or reduced to a rudiment between the tibia and the pretarsus.
For the most part the femur and tibia are the longest leg segments but variations in the lengths and robustness of each segment relate to their functions. For example, gressorial and cursorial, or walking and running type insects respectively, usually have well-developed femora and tibiae on all legs, whereas jumping (saltatorial) insects such as grasshoppers have disproportionately developed hind femora and tibiae. In aquatic beetles (Coleoptera) and bugs (Hemiptera
), the tibia
e and/or tarsi
of one or more pairs of legs usually are modified for swimming (natatorial) with fringes of long, slender hairs. Many ground-dwelling insects, such as mole crickets (Orthoptera: Gryllotalpidae), nymphal cicadas (Hemiptera: Cicadidae), and scarab beetles (Scarabaeidae
), have the tibiae of the fore legs enlarged and modified for digging (fossorial), whereas the fore legs of some predatory insects, such as mantispid lacewings (Neuroptera
) and mantids (Mantodea), are specialized for seizing prey, or raptorial. The tibia and basal tarsomere of each hind leg of honey bees are modified for the collection and carriage of pollen.
Generally, the first seven abdominal segments of adults (the pregenital segments) are similar in structure and lack appendages. However, apterygotes (bristletails and silverfish) and many immature aquatic insects have abdominal appendages. Apterygotes possess a pair of styles; rudimentary appendages that are serially homologous with the distal part of the thoracic legs. And, mesally, one or two pairs of protrusible (or exsertile) vesicles on at least some abdominal segments. These vesicles are derived from the coxal and trochanteral endites (inner annulated lobes) of the ancestral abdominal appendages. Aquatic larvae and nymphs may have gills laterally on some to most abdominal segments. Of the rest of the abdominal segments consist of the reproductive and anal parts.
The anal-genital part of the abdomen, known as the terminalia, consists generally of segments 8 or 9 to the abdominal apex. Segments 8 and 9 bear the genitalia; segment 10 is visible as a complete segment in many "lower” insects but always lacks appendages; and the small segment 11 is represented by a dorsal epiproct and pair of ventral paraprocts derived from the sternum. A pair of appendages, the cerci, articulates laterally on segment 11; typically these are annulated and filamentous but have been modified (e.g. the forceps of earwigs) or reduced in different insect orders. An annulated caudal filament, the median appendix dorsalis, arises from the tip of the epiproct in apterygotes, most mayflies (Ephemeroptera), and a few fossil insects. A similar structure in nymphal stoneflies (Plecoptera) is of uncertain homology. These terminal abdominal segments have excretory and sensory functions in all insects, but in adults there is an additional reproductive function.
The terminalia of adult female insects include internal structures for receiving the male copulatory organ and his spermatozoa and external structures used for oviposition (egg-laying; section 5.8). Most female insects have an egg-laying tube, or ovipositor; it is absent in termites, parasitic lice, many Plecoptera, and most Ephemeroptera. Ovipositors take two forms:
of an insect can be divided into a brain and a ventral nerve cord
. The head capsule is made up of six fused segments, each with a pair of ganglia
, or a cluster of nerve cells outside of the brain. The first three pairs of ganglia are fused into the brain, while the three following pairs are fused into a structure of three pairs of ganglia under the insect's esophagus
, called the subesophageal ganglion
.
The thoracic segments have one ganglion on each side, which are connected into a pair, one pair per segment. This arrangement is also seen in the abdomen but only in the first eight segments. Many species of insects have reduced numbers of ganglia due to fusion or reduction. Some cockroaches have just six ganglia in the abdomen, whereas the wasp Vespa crabro has only two in the thorax and three in the abdomen. Some insects, like the house fly Musca domestica
, have all the body ganglia fused into a single large thoracic ganglion.
At least a few insects have nociceptor
s, cells that detect and transmit sensations of pain
. This was discovered in 2003 by studying the variation in reactions of larvae
of the common fruitfly Drosophila
to the touch of a heated probe and an unheated one. The larvae reacted to the touch of the heated probe with a stereotypical rolling behavior that was not exhibited when the larvae were touched by the unheated probe. Although nociception has been demonstrated in insects, there is not a consensus that insects feel pain consciously.
s and other complex substances like protein
s, polysaccharide
s, fat
s, and nucleic acid
s. These macromolecules must be broken down by catabolic reaction
s into smaller molecules like amino acid
s and simple sugars before being used by cells of the body for energy, growth, or reproduction. This break-down process is known as digestion. The main structure of an insect's digestive system is a long enclosed tube called the alimentary canal, which runs lengthwise through the body. The alimentary canal directs food in one direction: from the mouth
to the anus
. It has three sections, each of which performs a different process of digestion. In addition to the alimentary canal, insects also have paired salivary glands and salivary reservoirs. These structures usually reside in the thorax, adjacent to the foregut. The gut is where almost all of insects' digestion takes place. It can be divided into the foregut
, midgut
and hindgut
.
(element 27 in numbered diagram), or stomodaeum. The foregut is line with a cuticular lining made of chitin
and protein
s as protection from tough food. The foregut includes the buccal cavity (mouth), pharynx
, esophagus
, and Crop
and proventriculus
(any part may be highly modified) which both store food and signify when to continue passing onward to the midgut. Here, digestion starts as partially chewed food is broken down by saliva from the salivary glands. As the salivary glands produce fluid and carbohydrate-digesting enzyme
s (mostly amylase
s), strong muscles in the pharynx pump fluid into the buccal cavity, lubricating the food like the salivarium does, and helping blood feeders, and xylem and phloem feeders.
From there, the pharynx passes food to the esophagus, which could be just a simple tube passing it on to the crop and proventriculus, and then on ward to the midgut, as in most insects. Alternately, the foregut may expand into a very enlarged crop and proventriculus, or the crop could just be a diverticulum
, or fluid filled structure, as in some Diptera species.
(element 13 in numbered diagram), also known as the mesenteron, where the majority of digestion takes place. Microscopic projections from the midgut wall, called microvilli
, increase the surface area of the wall and allow more nutrients to be absorbed; they tend to be close to the origin of the midgut. In some insects, the role of the microvilli and where they are located may vary. For example, specialized microvilli producing digestive enzymes may more likely be near the end of the midgut, and absorption near the origin or beginning of the midgut.
(element 16 in numbered diagram), or proctodaeum, undigested food particles are joined by uric acid
to form fecal pellets. The rectum absorbs 90% of the water in these fecal pellets, and the dry pellet is then eliminated through the anus (element 17), completing the process of digestion. The uric acid is formed using hemolymph waste products diffused from the Malpighian tubule
s (element 20). It is then emptied directly into the alimentary canal, at the junction between the midgut and hindgut. The number of Malpighian tubules possessed by a given insect varies between species, ranging from only two tubules in some insects to over 100 tubules in others.
s. Instead, the insect respiratory system uses a system of internal tubes and sacs through which gases either diffuse or are actively pumped, delivering oxygen directly to tissues that need it via their trachea
(element 8 in numbered diagram). Since oxygen is delivered directly, the circulatory system is not used to carry oxygen, and is therefore greatly reduced. The insect circulatory system has no vein
s or arterie
s, and instead consists of little more than a single, perforated dorsal tube which pulses peristaltically
. Toward the thorax, the dorsal tube (element 14) divides into chambers and acts like the insect's heart. The opposite end of the dorsal tube is like the aorta of the insect circulating the hemolymph
, arthropods' fluid analog of blood
, inside the body cavity. Air is taken in through openings on the sides of the abdomen called spiracle
s.
There are many different patterns of gas exchange
demonstrated by different groups of insects. Gas exchange patterns in insects can range from continuous and diffusive
ventilation, to discontinuous gas exchange
. During continuous gas exchange, oxygen
is taken in and carbon dioxide
is released in a continuous cycle. In discontinuous gas exchange, however, the insect takes in oxygen while it is active and small amounts of carbon dioxide are released when the insect is at rest. Diffusive ventilation is simply a form of continuous gas exchange that occurs by diffusion
rather than physically taking in the oxygen. Some species of insect that are submerged also have adaptations to aid in respiration. As larvae, many insects have gills that can extract oxygen dissolved in water, while others need to rise to the water surface to replenish air supplies which may be held or trapped in special structures.
, storage (water, carbohydrates and fats) and skeletal function. It also plays an essential part in the moulting process. An additional role of the haemolymph in some orders, can be that of predatory defence. It can contain unpalatable and malodourous chemicals that will act as a deterrent to predators. Haemolymph contains molecules, ions and cells; regulating chemical exchanges between tissues
, haemolymph is encased in the insect body cavity or haemocoel. It is transported around the body by combined heart (posterior) and aorta
(anterior) pulsations which are located dorsally just under the surface of the body. It differs from vertebrate
blood in that it doesn’t contain any red blood cells and therefore is without high oxygen carrying capacity, and is more similar to lymph
found in vertebrates.
Body fluids enter through one way valved ostia which are openings situated along the length of the combined aorta and heart organ. Pumping of the haemolymph occurs by waves of peristaltic contraction, originating at the body's posterior end, pumping forwards into the dorsal vessel, out via the aorta and then into the head where it flows out into the haemocoel. The haemolymph is circulated to the appendages unidirectionally with the aid of muscular pumps or accessory pulsatile organs which are usually found at the base of the antennae
or wings and sometimes in the legs, with pumping rates accelerating with periods of increased activity. Movement of haemolymph is particularly important for thermoregulation in orders such as Odonata
, Lepidoptera
, Hymenoptera
and Diptera
.
s (element 30 in numbered diagram) in an insect's mouth produce saliva. The salivary ducts lead from the glands to the reservoirs and then forward through the head to an opening called the salivarium, located behind the hypopharynx. By moving its mouthparts (element 32 in numbered diagram) the insect can mix its food with saliva. The mixture of saliva and food then travels through the salivary tubes into the mouth, where it begins to break down. Some insects, like flies
, have extra-oral digestion
. Insects using extra-oral digestion expel digestive enzymes onto their food to break it down. This strategy allows insects to extract a significant proportion of the available nutrients from the food source.
e, and ducts connecting these parts. The ovaries make eggs and accessory glands produce the substances to help package and lay the eggs. Spermathecae store sperm for varying periods of time and, along with portions of the oviduct
s, can control sperm use. The ducts and spermathecae are lined with a cuticle.
The ovaries are made up of a number of egg tubes, called ovarioles
, which vary in size and number by species. The number of eggs that the insect is able to make vary by the number of ovarioles with the rate that eggs can be develop being also influenced by ovariole design. In meroistic ovaries, the eggs-to-be divide repeatedly and most of the daughter cells become helper cells for a single oocyte
in the cluster. In panoistic ovaries, each egg-to-be produced by stem germ cells develops into an oocyte; there are no helper cells from the germ line. Production of eggs by panoistic ovaries tends to be slower than that by meroistic ovaries.
Accessory glands or glandular parts of the oviducts produce a variety of substances for sperm maintenance, transport, and fertilization, as well as for protection of eggs. They can produce glue and protective substances for coating eggs or tough coverings for a batch of eggs called ootheca
e. Spermathecae are tubes or sacs in which sperm can be stored between the time of mating and the time an egg is fertilized. Paternity testing of insects has revealed that some, and probably many, female insects use the spermatheca and various ducts to control or bias sperm used in favor of some males over others.
e and the fat body. The more primitive apterygote
insects have a single testis, and in some lepidopterans
the two maturing testes are secondarily fused into one structure during the later stages of larval development, although the ducts leading from them remain separate. However, most male insects have a pair of testes, inside of which are sperm tubes or follicles that are enclosed within a membranous sac. The follicles connect to the vas deferens by the vas efferens, and the two tubular vasa deferentia connect to a median ejaculatory duct that leads to the outside. A portion of the vas deferens is often enlarged to form the seminal vesicle, which stores the sperm before they are discharged into the female. The seminal vesicles have glandular linings that secrete nutrients for nourishment and maintenance of the sperm. The ejaculatory duct is derived from an invagination of the epidermal cells during development and, as a result, has a cuticular lining. The terminal portion of the ejaculatory duct may be sclerotized to form the intromittent organ, the aedeagus. The remainder of the male reproductive system is derived from embryonic mesoderm, except for the germ cells, or spermatogonia, which descend from the primordial pole cells very early during embryogenesis.
-eating species such as Cryptocercus
; these roaches are incapable of digesting cellulose
themselves, but have symbiotic relationships with various protozoa
ns and bacteria
that digest the cellulose, allowing them to extract the nutrients. The similarity of these symbionts in the genus Cryptocercus to those in termite
s are such that it has been suggested that they are more closely related to termite
s than to other cockroaches, and current research strongly supports this hypothesis of relationships. All species studied so far carry the obligate mutualistic endosymbiont bacterium Blattabacterium
, with the exception of Nocticola australiensis, an Australian cave dwelling species without eyes, pigment or wings, and which recent genetic studies indicates are very primitive cockroaches.
Cockroaches, like all insects, breathe through a system of tubes called tracheae
. The tracheae of insects are attached to the spiracle
s, excluding the head. Thus cockroaches, like all insects, are not dependent on the mouth and windpipe to breathe. The valves open when the CO2
level in the insect rises to a high level; then the CO2 diffuses
out of the tracheae to the outside and fresh O2 diffuses in. Unlike in vertebrates that depend on blood
for transporting O2 and CO2, the tracheal system brings the air directly to cells
, the tracheal tubes branching continually like a tree until their finest divisions, tracheoles, are associated with each cell, allowing gaseous oxygen to dissolve in the cytoplasm lying across the fine cuticle lining of the tracheole. CO2 diffuses out of the cell into the tracheole. While cockroaches do not have lungs and thus do not actively breathe in the vertebrate lung manner, in some very large species the body musculature may contract rhythmically to forcibly move air out and in the spiracles; this may be considered a form of breathing.
performing digestion. Although, in predatory species (e.g., Carabidae) most digestion occurs in the crop by means of midgut enzymes. In Elateridae species, the predatory larvae defecate enzymes on their prey, with digestion being extraorally. The alimentary canal basically comprises a short narrow pharynx
, a widened expansion, the crop
and a poorly developed gizzard
. After there is a midgut, that varies in dimensions between species, with a large amount of cecum
, with a hingut, with varying lengths. There are typically four to six Malpighian tubules.
The nervous system
in beetles contains all the types found in insects, varying between different species. With three thoracic and seven or eight abdominal ganglia can be distinguished to that in which all the thoracic and abdominal ganglia are fused to form a composite structure. Oxygen
is obtained via a tracheal system
. Air enters a series of tubes along the body through openings called spiracle
s, and is then taken into increasingly finer fibers. Pumping movements of the body force the air through the system. Beetles have hemolymph
instead of blood
like other insect species, the open circulatory system of the beetle is driven by a tube-like heart attached to the top inside of the thorax. Some species of diving beetle
s (Dytiscidae) carry a bubble of air with them whenever they dive beneath the water surface. This bubble may be held under the elytra or it may be trapped against the body using specialized hairs. The bubble usually covers one or more spiracles so the insect can breathe air from the bubble while submerged. An air bubble provides an insect with only a short-term supply of oxygen, but thanks to its unique physical properties, oxygen will diffuse into the bubble and displacing the nitrogen, called passive diffusion, however the volume of the bubble eventually diminishes and the beetle will have to return to the surface.
Different glands specialize for different pheromones produced for finding mates. Pheromones from species of Rutelinea are produced from epithelial cell
s lining the inner surface of the apical abdominal segments or amino acid based pheromones of Melolonthinae
from eversible glands on the abdominal apex. Other species produce different types of pheromones. Dermestids produce ester
s, and species of Elateridae produce fatty-acid-derived aldehyde
s and acetate
s. For means of finding a mate also, fireflies (Lampyridae) utilized modified fat body cells woth transparent surfaces backed with reflective uric acid crystals to biosynthetically produce light, or bioluminescence
. The light produce is highly efficient, as it is produced by oxidation of luciferin
by the enzymes luciferase
in the presence of ATP
(adenosine triphospate) and oxygen, producing oxyluciferin, carbon dioxide, and light.
A notable number of species have developed special glands that produce chemicals for deterring predators (see Defense and predation). The Ground beetle
's (of Carabidae) defensive glands, located at the posterior, produce a variety of hydrocarbon
s, aldehyde
s, phenol
s, quinone
s, ester
s, and acid
s released from an opening at the end of the abdomen. While African carabid beetles (e.g., Anthia some of which used to comprise the genus Thermophilum) employ the same chemicals as ants: formic acid
. While Bombardier beetle
s have well developed, like other carabid beetles, pygidial glands that empty from the lateral edges of the intersegment membranes between the seventh and eighth abdominal segments. The gland is made of two containing chambers. The first holds hydroquinone
s and hydrogen peroxide
, with the second holding just hydrogen peroxide plus catalase
s. These chemicals mix and result in an explosive ejection, forming temperatures of around 100 C, with the brake down of hydroquinone to H2 + O2 + quinone, with the O2 propelling the excretion.
Tympanal organ
s or hearing organs, which is a membrane (tympanum) stretched across a frame backed by an air sac and associated sensory neurons, are described in two families. Several species of the genus Cicindela
(Cicindelidae) have ears on the dorsal surface of the first abdominal segment beneath the wing; two tribes tribes in the family Dynastinae (Scarabaeidae
) have ears just beneath the pronotal shield or neck membrane. The ears of both families are to ultrasonic frequencies, with strong evidence that they function to detect the presence of bats via there ultrasonic echolocation. Even though beetles constitute a large order and live in a variety of niche
s, examples of hearing is surprisingly lacking in species, though it is likely that most are just undiscovered.
consist of what typical insect would. There is a Brain
, a subesophageal ganglion, three thoratic ganglia, and six abdominal ganglia; a ganglion being a mass of neuron
s.
Strong neuron connects connect the neurohemal corpora cardiaca to the brain and frontal ganglion, where the closely related median corpus allatum
produces Jeuvenile hormone III in close proximity to the neurohemal dorsal arota. The digestive system of earwigs is like all other insects: consisting of a fore-, mid-, and hindgut, albeit, earwigs lack gastric caecae which specialize in many species of insects for digestion. Long, slender (extratory) malpighian tubules can be found between the junction of the mid- and hind gut.
The reproductive system of females consist of paired ovarie
s, lateral oviduct
s, spermatheca
, and a genital chamber
. The lateral ducts are where the eggs leave the body, while the spermatheca is where sperm is stored. Unlike other insects, the gonopore
, or genital opening is behind the seventh abdominal segment. The ovaries are primitive in that they are polytrophic; or the nurse cell
s and oocyte
s alternate along the length of the ovariole. In some species these long ovarioles branch off the lateral duct, while in others, short ovarioles appear around the duct.
being located below the genitals, or, in the case of 360° torsion, to the sperm duct being wrapped around the gut, despite the external organs being in their usual position. When flies mate, the male initially flies on top of the female, facing in the same direction, but then turns round to face in the opposite direction. This forces the male to lie on its back in order for its genitalia to remain engaged with those of the female, or the torsion of the male genitals allows the male to mate while remaining upright. This leads to flies having more reproduction abilities than most insects and at a much quicker rate. Flies come in great populations due ir ability to mate effectively and in a short period of time especially during the mating season.
The female lays her eggs as close to the food source as possible, and development is very rapid, allowing the larva to consume as much food as possible in a short period of time before transforming into the adult. The eggs hatch immediately after being laid, or the flies are ovoviviparous, with the larva hatching inside the mother. Larval flies, or maggot
s, have no true legs, and little demarcation between the thorax and abdomen
; in the more derived species, the head is not clearly distinguishable from the rest of the body. Maggots are limbless, or else have small proleg
s. The eyes and antennae are reduced or absent, and the abdomen also lacks appendages such as cerci
. This lack of features is an adaptation to a food-rich environment, such as within rotting organic matter, or as an endoparasite. The pupa
e take various forms, and in some cases develop inside a silk cocoon. After emerging from the pupa, the adult fly rarely lives more than a few days, and serves mainly to reproduce and to disperse in search of new food sources.
of butterflies and moths, the male genitalia are complex and unclear. In females there are three types of genitalia based on the relating taxa: monotrysian, exoporian, and dytresian. In the monotrysian type there is an opening on the fused segments of the sterna 9 and 10, which act as insemination and oviposition. In the exoporian type (in Hepaloidae and Mnesarchaeoidea) there are two separate places for insemination and oviposition, both occurring on the same sterna as the monotrysian type, 9/10. In most species the genitalia are flanked by two soft lobes, although they may be specialized and sclerotized in some species for ovipositing in area such as crevices and inside plant tissue. Hormones and the glands that produce them run the development of butterflies and moths as they go through their life cycle, called the endocrine system
. The first insect hormone PTTH
(Prothoracicotropic hormone) operates the species life cycle and diapause (see the relates section). This hormone is produced by corpora allata
and corpora cardiaca, where it is also stored. Some glands are specialized to perform certain task such as producing silk or producing saliva in the palpi. While the corpora cardiaca produce PTTH, the corpora allata also produces jeuvanile hormones, and the prothorocic glands produce moulting hormones.
In the digestive system, the anterior region of the foregut has been modified to form a pharyngial
sucking pump as they need it for the food they eat, which are for the most part liquids. An esophagus
follows and leads to the posterior of the pharynx and in some species forms a form of crop. The midgut is short and straight, with the hindgut being longer and coiled. Ancestors of lepidopteran species, stemming from Hymenoptera
, had midgut ceca, although this is lost in current butterflies and moths. Instead, all the digestive enzymes other than initial digestion, are immobilized at the surface of the midgut cells. In larvae, long-necked and stalked goblet cell
s are found in the anterior and posterior midgut regions, respectively. In insects, the goblet cells excrete positive potassium
ions, which are absorbed from leaves ingested by the larvae. Most butterflies and moths display the usual digestive cycle, however species that have a different diet require adaptations to meet these new demands.
In the circulatory system
, hemolymph
, or insect blood, is used to circulate heat in a form of thermoregulation
, where muscles contraction produces heat which is transferred to the rest of the body when conditions are unfavorable. In lepidopteran species, hemolymph is circulated through the veins in the wings by some form of pulsating organ, either by the heart or by the intake of air into the trachea
. Air is taken in through spiracles along the sides of the abdomen and thorax supplying the trachea with oxygen as it goes through the lepidopteran's respiratory system
. There are three different tracheae supplying oxygen diffusing oxygen throughout the species body: The dorsal, ventral, and visceral. The dorsal tracheae supply oxygen to the dorsal musculature and vessels, while the ventral tracheae supply the ventral musculature and nerve cord, and the visceral tracheae supply the guts, fat bodies, and gonad
s.
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
of insects enables the phenomenal success of this class
Class (biology)
In biological classification, class is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, order, family, genus, and species, with class fitting between phylum and order...
of arthropods. The sheer quantity and diversity of its taxa
Taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...
are matched by a large variation of modifications in its body structure. The high rate of speciation
Speciation
Speciation is the evolutionary process by which new biological species arise. The biologist Orator F. Cook seems to have been the first to coin the term 'speciation' for the splitting of lineages or 'cladogenesis,' as opposed to 'anagenesis' or 'phyletic evolution' occurring within lineages...
, short generations and long lineage have caused insects to evolve in many ways resulting in very large variations in morphology. These modifications allow insects to occupy almost every ecological niche
Ecological niche
In ecology, a niche is a term describing the relational position of a species or population in its ecosystem to each other; e.g. a dolphin could potentially be in another ecological niche from one that travels in a different pod if the members of these pods utilize significantly different food...
, utilise a staggering variety of food sources and possess diverse lifestyles. Insect body sizes range from 0.3 mm in the case of mymarid wasps which parasitise insect eggs to the 30 cms wingspan of the American owlet moth Thysania agrippina (family Noctuidae
Noctuidae
The Noctuidae or owlet moths are a family of robustly-built moths that includes more than 35,000 known species out of possibly 100,000 total, in more than 4,200 genera. They constitute the largest family in the Lepidoptera....
).
Insects are by far the most successful group in the Arthropoda. They differ in significant ways from the other classes of Hexapoda
Hexapoda
The subphylum Hexapoda constitutes the largest grouping of arthropods and includes the insects as well as three much smaller groups of wingless arthropods: Collembola, Protura, and Diplura . The Collembola are very abundant in terrestrial environments...
, such as Protura, Collembola and others) who are now considered by some authorities to be more basal
Basal (phylogenetics)
In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
than insects.
Summary
Insects possess segmentSegmentation (biology)
Segmentation in biology refers to either a type of gastrointestinal motility or the division of some animal and plant body plans into a series of repetitive segments. This article will focus on the segmentation of animal body plans, specifically using the examples of the phyla Arthropoda,...
ed bodies supported by an exoskeleton
Exoskeleton
An exoskeleton is the external skeleton that supports and protects an animal's body, in contrast to the internal skeleton of, for example, a human. In popular usage, some of the larger kinds of exoskeletons are known as "shells". Examples of exoskeleton animals include insects such as grasshoppers...
, a hard jointed outer covering made mostly of chitin
Chitin
Chitin n is a long-chain polymer of a N-acetylglucosamine, a derivative of glucose, and is found in many places throughout the natural world...
. The segments of the body are organized into three distinctive but interconnected units, or tagmata
Tagma (biology)
In invertebrate biology, a tagma is a specialized grouping of arthropod segments, such as the head, the thorax, and the abdomen with a common function. The segments of a tagma may be either fused or moveable.-Tagmata:...
; a head, a thorax
Thorax (insect anatomy)
The thorax is the mid section of the insect body. It holds the head, legs, wings and abdomen. It is also called mesosoma in other arthropods....
, and an abdomen
Abdomen
In vertebrates such as mammals the abdomen constitutes the part of the body between the thorax and pelvis. The region enclosed by the abdomen is termed the abdominal cavity...
. The head supports a pair of sensory antennae
Antenna (biology)
Antennae in biology have historically been paired appendages used for sensing in arthropods. More recently, the term has also been applied to cilium structures present in most cell types of eukaryotes....
, a pair of compound eyes, if present, one to three simple eyes or (ocelli) and three sets of variously modified appendages that form the mouthparts
Insect mouthparts
Insects exhibit a range of mouthparts, adapted to particular modes of feeding. The earliest insects had chewing mouthparts...
. The thorax has six segmented legs
Arthropod leg
The arthropod leg is a form of jointed appendage of arthropods, usually used for walking. Many of the terms used for arthropod leg segments are of Latin origin, and may be confused with terms for bones: coxa , trochanter , femur, tibia, tarsus, ischium, metatarsus, carpus, dactylus ,...
(one pair each for the prothorax, mesothorax and the metathorax segments making up the thorax) and two or four wings
Insect wing
Insects are the only group of invertebrates known to have evolved flight. Insects possess some remarkable flight characteristics and abilities, still far superior to attempts by humans to replicate their capabilities. Even our understanding of the aerodynamics of flexible, flapping wings and how...
(if present in the species). The abdomen (made up of eleven segments some of which may be reduced or fused) has most of the digestive
Digestion
Digestion is the mechanical and chemical breakdown of food into smaller components that are more easily absorbed into a blood stream, for instance. Digestion is a form of catabolism: a breakdown of large food molecules to smaller ones....
, respiratory
Respiration (physiology)
'In physiology, respiration is defined as the transport of oxygen from the outside air to the cells within tissues, and the transport of carbon dioxide in the opposite direction...
, excretory
Excretion
Excretion is the process by which waste products of metabolism and other non-useful materials are eliminated from an organism. This is primarily carried out by the lungs, kidneys and skin. This is in contrast with secretion, where the substance may have specific tasks after leaving the cell...
and reproductive internal structures. There is considerable variation and many adaptations in the body parts of insects especially wings, legs, antenna, mouth-parts etc.
Exoskeleton
Their outer skeleton, the cuticleCuticle
A cuticle , or cuticula, is a term used for any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Various types of "cuticles" are non-homologous; differing in their origin, structure, function, and chemical composition...
, is made up of two layers; the epicuticle which is a thin and waxy water resistant outer layer and contains no chitin, and another layer under it called the procuticle. This is chitinous and much thicker than the epicuticle and has two layers, the outer being the exocuticle while the inner is the endocuticle. The tough and flexible endocuticle is built from numerous layers of fibrous chitin and proteins, criss-crossing each others in a sandwich pattern, while the exocuticle is rigid and sclerotized. The exocuticle is greatly reduced in many soft-bodied insects, especially the larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
l stages (e.g., caterpillar
Caterpillar
Caterpillars are the larval form of members of the order Lepidoptera . They are mostly herbivorous in food habit, although some species are insectivorous. Caterpillars are voracious feeders and many of them are considered to be pests in agriculture...
s). Chemically chitin is a long-chain polymer
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...
of a N-acetylglucosamine
N-Acetylglucosamine
N-Acetylglucosamine is a monosaccharide derivative of glucose. It is an amide between glucosamine and acetic acid...
, a derivative of glucose. In its unmodified form, chitin is translucent, pliable, resilient and quite tough. In arthropod
Arthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...
s, however, it is often modified, becoming embedded in a hardened protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
aceous matrix, which forms much of the exoskeleton
Exoskeleton
An exoskeleton is the external skeleton that supports and protects an animal's body, in contrast to the internal skeleton of, for example, a human. In popular usage, some of the larger kinds of exoskeletons are known as "shells". Examples of exoskeleton animals include insects such as grasshoppers...
. In its pure form it is leathery, but when encrusted in calcium carbonate
Calcium carbonate
Calcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks in all parts of the world, and is the main component of shells of marine organisms, snails, coal balls, pearls, and eggshells. Calcium carbonate is the active ingredient in agricultural lime,...
it becomes much harder. The difference between the unmodified and modified forms can be seen by comparing the body wall of a caterpillar
Caterpillar
Caterpillars are the larval form of members of the order Lepidoptera . They are mostly herbivorous in food habit, although some species are insectivorous. Caterpillars are voracious feeders and many of them are considered to be pests in agriculture...
(unmodified) to a beetle
Beetle
Coleoptera is an order of insects commonly called beetles. The word "coleoptera" is from the Greek , koleos, "sheath"; and , pteron, "wing", thus "sheathed wing". Coleoptera contains more species than any other order, constituting almost 25% of all known life-forms...
(modified).
From the embryonic stages itself, a layer of columnar or cuboidal epithelial cells give rise to the external cuticle and an internal basement membrane. The majority of insect material is held in the endocuticle. The cuticle provides muscular support and acts as a protective shield as the insect develops. However since it cannot grow the external sclerotised part of the cuticle is periodically shed in a process called "moulting". As the time for moulting approaches, most of the exocuticle material is reabsorbed. In moulting, first the old cuticle separates from the epidermis (apodysis). Enzymatic moulting fluid is released in between the old cuticle and epidermis which separates the exocuticle by digesting the endocuticle and sequestering its material for the new cuticle. When the new cuticle has formed sufficiently, the epicuticle and reduced exocuticle are shed in ecdysis
Ecdysis
Ecdysis is the moulting of the cuticula in many invertebrates. This process of moulting is the defining feature of the clade Ecdysozoa, comprising the arthropods, nematodes, velvet worms, horsehair worms, rotifers, tardigrades and Cephalorhyncha...
.
There are four principal regions of an insect body segment: tergum
Tergum
A tergum is the dorsal portion of an arthropod segment other than the head. The anterior edge is called the base and posterior edge is called the apex or margin. A given tergum may be divided into hardened plates or sclerites commonly referred to as tergites...
or dorsal, sternum
Sternum
The sternum or breastbone is a long flat bony plate shaped like a capital "T" located anteriorly to the heart in the center of the thorax...
or ventral and the two pleura or lateral. Hardened plates in the exoskeleton are called sclerites. Sclerites that are subdivisions of the major regions are tergites, sternites and pleurites, for the respective regions tergum, sternum and pleuron.
Head
The headHead
In anatomy, the head of an animal is the rostral part that usually comprises the brain, eyes, ears, nose and mouth . Some very simple animals may not have a head, but many bilaterally symmetric forms do....
is enclosed in a hard, heavily sclerotized, unsegmented, exoskeletal head capsule, or epicranium
Epicranium
The Epicranium is the medical term for the collection of structures covering the cranium. It consists of the muscles, aponeurosis, and skin....
, which contains most of the sensing organs, including the antennae, ocellus or eyes, and the mouthparts. Out of all the insect orders, Orthoptera displays the most features found in other insects, including the sutures and sclerite
Sclerite
A sclerite is a hardened body part. The term is used in various branches of biology for various structures including hardened portions of sponges, but it is most commonly used for the hardened portions of arthropod exoskeletons....
s. here, the vertex
Vertex
Vertex may refer to:-Mathematics:*Vertex , an angle point of any shape or angle*Vertex , a node in a graph*Vertex , a local extreme point of curvature...
, or the apex (dorsal region), is situated between the compound eyes for insects with a hypognathous and opisthognathous head. In prognathous insects, the vertex is not found between the compound eyes, but rather, where the ocelli
Ocellus
A simple eye refers to a type of eye design or optical arrangement that contains a single lens which detect light. A "simple eye" is so-called in distinction from a multi-lensed "compound eye", and is not necessarily at all simple in the usual sense of the word...
are normally. This is because the primary axis of the head is rotated 90 degrees to become parallel to the primary axis of the body. In some species this region is modified and assumes a different name.
The ecdysial suture is made of the coronal, frontal, epicranial sutures plus the ecdysial and cleavage lines; which is varies among different species of insects. The ecdysial suture is longitudinally placed on the vertex and separates the epicranial halves of the head to the left and right sides. Depending in the insect, the suture may come in different shapes: like either a Y, U, or V. those diverging lines that make up the ecdysial suture are called the frontal sutures or fontogenal sutures. Not all species of insect have frontal sutures, but in those who do, it helps the individual emerge from the integument when molting. The frons
Frons
Frons is the term used to describe the frontal area of an insect's head. It covers the upper part of the face above the clypeus and below and between the antennae. It supports the pharyngeal dilator muscles and usually bears an ocellus . The term itself is derived from the Latin frons "forehead"....
is that part of the head that is ventrad, or towards the ventral and lower, of the vertex. the frons varies in size and is sometimes hard to identify, especially its borders in some species. However in most species, the frons is separated by the frontoclypeal or epistomal sutures; a transverse suture located under the antennae sockets.
The clypeus
Clypeus
The clypeus is one of the sclerites that makes up the "face" of an arthropod.In insects, the clypeus delimits the lower margin of the face, with the labrum articulated along the ventral margin of the clypeus. The mandibles bracket the labrum, but do not touch the clypeus. The dorsal margin of the...
is a sclerite between the face and labrum, which is dorsally separated from the frons by the frontoclypeal suture in primitive insects. The clypeogenal suture laterally democrates the clypeus, with the clypeus ventrally separated from the labrum by the clypeolabral suture. The clypeus differs in shape and size, such as species of Lepidoptera with a large clypeus with elongated mouthparts. The cheek or gena
GENA
GENA stands for General Event Notification Architecture.GENA Base defines an HTTP notification architecture that transmits notifications between HTTP resources. An HTTP resource could be any object which might need to send or receive a notification, for example a distribution list, buddy list,...
forms the sclerotized area on each side of the head below the compound eyes extending to the gular suture. Like many of the other parts making up the insect's head, the gena varies among species with its boundaries difficult to establish. For example, in dragonflies and damselflies (Odonata
Odonata
Odonata is an order of insects, encompassing dragonflies and damselflies . The word dragonfly is also sometimes used to refer to all Odonata, but the back-formation odonate is a more correct English name for the group as a whole...
) is between the compound eyes, clypeus, and mouthparts. The postgena is the area immediately posteriad, or posterior or lower of the gena of pterygote insect
Pterygota
Pterygota is a subclass of insects that includes the winged insects. It also includes insect orders that are secondarily wingless ....
s and form the lateral and ventral parts of the occipital arch. The occipital arch is a narrow band forming the posterior edge of the head capsule arching dorsally over the foramen. The subgenal area is usually narrow, located above the mouthparts; this area also includes the hypostoma and pleurostoma
Pleurostoma
Pleurostoma is a genus of fungi in the family Pleurostomataceae containing 2 species....
. The vertex extends anteriorly above the bases of the antennae as a prominent, pointed, concave rostrum. The posterior wall of the head capsule is penetrated by a large aperture, the foramen. Through it pass the organ systems, such as nerve cord
Nerve cord
Nerve cord may refer to the following structures:* in invertebrates, it refers to the ventral nerve cord, whereas* in chordates, it stands for the dorsal nerve cord....
, esophagus
Esophagus
The esophagus is an organ in vertebrates which consists of a muscular tube through which food passes from the pharynx to the stomach. During swallowing, food passes from the mouth through the pharynx into the esophagus and travels via peristalsis to the stomach...
, salivary duct
Salivary duct
Salivary duct may refer to:* Parotid duct* Submaxillary duct* Major sublingual duct...
s, and musculature, connecting the head with the thorax
Thorax (insect anatomy)
The thorax is the mid section of the insect body. It holds the head, legs, wings and abdomen. It is also called mesosoma in other arthropods....
.
Of the posterior aspect of the head, included are the occiput
Occiput
The occiput is the anatomical term for the posterior portion of the head, in insects the posterior part of those head capsule.-Clinical significance:Trauma to the occiput can cause a basilar skull fracture....
, postgena, occipital formen, posterior tentorial pit, gula
Gula
Nintinugga was a Babylonian goddess of healing, the consort of Ninurta. She is identical with another goddess, known as Bau, though it would seem that the two were originally independent....
, postgenal bridge, the hypostomal suture and bridge, and the mandibles, labium
Labium
The labia are anatomical structures that are part of the female genitalia; they are the major externally visible portions of the vulva. In humans, there are two pairs of labia: the outer labia, or labia majora are larger and fattier, while the labia minora are folds of skin often concealed within...
, and maxilla
Maxilla
The maxilla is a fusion of two bones along the palatal fissure that form the upper jaw. This is similar to the mandible , which is also a fusion of two halves at the mental symphysis. Sometimes The maxilla (plural: maxillae) is a fusion of two bones along the palatal fissure that form the upper...
. The occiputal suture is well founded in species of Orthoptera, but not so much in other orders. Where found, the occipital suture is arched, horseshoe-shaped groove on the back of the head, ending at the posterior of each mandible. The postoccipital suture is a landmark on the posterior surface of the head and is typically near the occipital foremen. In pterygotes, the postocciput forms the extreme posterior, often U-shaped which forms the rim of the head extending to the postoccipital suture. In pterygotes, such as those of Orthoptera, the occipital foramen and the mouth are not separated. The three types of occipital closures, or points under the occipital foramen that separate the two lower halves of the postgena: the hypostomal bridge, postgenal bridge, and the gula. The hypstosaml bridge is usually found in insects with hypognathous orientation. The postgenal bridge is found in the adult species of higher Diptera
Diptera
Diptera , or true flies, is the order of insects possessing only a single pair of wings on the mesothorax; the metathorax bears a pair of drumstick like structures called the halteres, the remnants of the hind wings. It is a large order, containing an estimated 240,000 species, although under half...
, and aculeate Hymenoptera
Hymenoptera
Hymenoptera is one of the largest orders of insects, comprising the sawflies, wasps, bees and ants. There are over 130,000 recognized species, with many more remaining to be described. The name refers to the heavy wings of the insects, and is derived from the Ancient Greek ὑμήν : membrane and...
, while the gula is found on some Coleoptera, Neuroptera
Neuroptera
The insect order Neuroptera, or net-winged insects, includes the lacewings, mantidflies, antlions, and their relatives. The order contains some 6,010 species...
,and Isoptera which typically display a prognathous orientated mouthparts.
Compound eyes and ocelli
In most insects there is one pair of large, prominent compound eyes composed of units called ommatidia (ommatidiumOmmatidium
The compound eyes of insects, mantis shrimp and millipedes are composed of units called ommatidia . An ommatidium contains a cluster of photoreceptor cells surrounded by support cells and pigment cells. The outer part of the ommatidium is overlaid with a transparent cornea...
, singular), of which there may be up to 30,000 ommatidia in a single compound eye. This type of eye gives less resolution than eyes found in vertebrates, but it gives acute perception of movement. There can also be an additional two or three ocelli, which help detect low light or small changes in light intensity. The image perceived is a combination of inputs from the numerous ommatidia, which are located on a convex surface, thus pointing in slightly different directions. Compared with simple eyes, compound eyes possess a very large view angle, and can detect fast movement and, in some cases, the polarization of light.
Because the individual lenses are so small, the effects of diffraction
Diffraction
Diffraction refers to various phenomena which occur when a wave encounters an obstacle. Italian scientist Francesco Maria Grimaldi coined the word "diffraction" and was the first to record accurate observations of the phenomenon in 1665...
impose a limit on the possible resolution that can be obtained (assuming that they do not function as phased array
Phased array
In wave theory, a phased array is an array of antennas in which the relative phases of the respective signals feeding the antennas are varied in such a way that the effective radiation pattern of the array is reinforced in a desired direction and suppressed in undesired directions.An antenna array...
s). This can only be countered by increasing lens size and number. To see with a resolution comparable to our simple eyes, humans would require compound eyes which would each reach the size of their head. Compound eyes fall into two groups: apposition eyes, which form multiple inverted images, and superposition eyes, which form a single erect image. Compound eyes grow at their margins by the addition of new ommatidia.
Antennae
The antennaAntenna (biology)
Antennae in biology have historically been paired appendages used for sensing in arthropods. More recently, the term has also been applied to cilium structures present in most cell types of eukaryotes....
e function almost exclusively in sensory perception, some of the sensory uses of antennae include motion and orientation, odor, sound, humidity, and a variety of chemical cues. Antennae vary greatly among insects, but all follow a basic plan, of which include the first and second segments are termed the scape and pedicel, respectively. The remaining antennal segments or flagellomeres are jointly called the flagellum
Flagellum
A flagellum is a tail-like projection that protrudes from the cell body of certain prokaryotic and eukaryotic cells, and plays the dual role of locomotion and sense organ, being sensitive to chemicals and temperatures outside the cell. There are some notable differences between prokaryotic and...
. There are many different types of antennae among different species, including setaceous, moniliform, serrate, pectinate, clavate, lamellate, geniculate, and plumose.
- Aristate: These forms of antennae are pouch-like with a lateral bristle.(e.g. DipteraDipteraDiptera , or true flies, is the order of insects possessing only a single pair of wings on the mesothorax; the metathorax bears a pair of drumstick like structures called the halteres, the remnants of the hind wings. It is a large order, containing an estimated 240,000 species, although under half...
)
- Filiform: These forms of antennae are common amongst many different genera, which have a simple thread-like shape.
- Setaceous: These forms of antennae have many joints. The antenna tapers gradually from the base to the tip (e.g. ThysanuraThysanuraThysanura is an order of insects, encompassing silverfish and firebrats, known for their three long caudal filaments.The families Machilidae and Meinertellidae of the jumping bristletails were once included with Thysanura....
, Blattodea, Ephemeroptera, PlecopteraPlecopteraPlecoptera are an order of insects, commonly known as stoneflies. There are some 3,500 described species worldwide, with new species still being discovered. Stoneflies are found worldwide, except Antarctica...
and TrichopteraTrichopteraThe caddisflies are an order, Trichoptera, of insects with approximately 12,000 described species. Also called sedge-flies or rail-flies, they are small moth-like insects having two pairs of hairy membranous wings...
).
- Moniliform: These forms of antennae have round segments that make the antenna look like a string of beads (e.g. Coleoptera)
- Serrate: These forms of antennae have segments that are angled on one side giving the appearance of a saw edge (e.g. Coleoptera)
- Pectinate: These forms of antennae have segments that are longer on one side giving the appearance of a comb (e.g. Hemynoptera - Symphyta sp. and Coleoptera).
- Clavate: These forms of antennae have segments that become wider towards the tip of the antenna. This may be gradual along its length, or a sudden increase (Capitate) and therefore mainly affecting the last few joints and giving the appearance of a club (e.g. LepidopteraLepidopteraLepidoptera is a large order of insects that includes moths and butterflies . It is one of the most widespread and widely recognizable insect orders in the world, encompassing moths and the three superfamilies of butterflies, skipper butterflies, and moth-butterflies...
and Coleoptera)
- Lamellate: These forms of antennae have segments that towards the end are flattened and plate-like. This gives the appearance of a fan towards the end of the antennae. (e.g. Coleoptera - ScarabaeidaeScarabaeidaeThe family Scarabaeidae as currently defined consists of over 30,000 species of beetles worldwide. The species in this large family are often called scarabs or scarab beetles. The classification of this family is fairly unstable, with numerous competing theories, and new proposals appearing quite...
sp.)
- Geniculate: In these forms of antennae, there is an abrupt bend or elbow part of the way along the antenna (e.g. Hymenoptera - Formicidae sp. and Coleoptera).
- Plumose: These forms of antennae have segments which each have a number of fine thread-like branches. This gives the appearance of a feather (e.g. DipteraDipteraDiptera , or true flies, is the order of insects possessing only a single pair of wings on the mesothorax; the metathorax bears a pair of drumstick like structures called the halteres, the remnants of the hind wings. It is a large order, containing an estimated 240,000 species, although under half...
)
Mouthparts
The insect mouthparts consist of the maxilla, libium, and in some species the mandibles. The labrum is a simple fused sclerite, often called the upper lip and moves longitudinally which is hinged to the clypeus. The mandibles (jaws) are a highly sclerotized pair of structures that move at right angles to the body; used for biting, chewing and severing food. The maxillae are paired structures that can also move at right angles to the body and possess segmented palps. The labium (lower lip) is the fused structure that moves longitudinally and possesses a pair of segmented palps.The mouthparts, along with the rest of the head, can be articulated in at least three different positions: prognathous, opisthognathous and hypognathous. In species with prognathous articulation, the head is positioned vertically aligned with the body, such as species of Formicidae; while in a hypognathous type, the head is aligned horizontally adjacent to the body. In a opisthognathous head, it was positioned diagonally, such as species of Blattodea and some Coleopterans. The mouthparts very greatly among insects of different orders but there are two main functional groups: mandibulate and haustellate. Haustellate mouthparts are those used for sucking liquids and can be further classified, by the presence of stylet
Stylet
A stylet is a hard, sharp, anatomical structure found in some invertebrates.For example, the word stylet or stomatostyle, is used for the primitive piercing mouthparts of some nematodes and some nemerteans...
s, which include: piercing-sucking, sponging, and siphoning. The stylets are needle-like projections used to penetrate plant and animal tissue. The stylets and the feeding tube form the modified mandibles, maxilla, and hypopharynx.
- Mandibulate: These forms of mouthparts are among the most common in insects, which are used for biting and grinding solid foods.
- Piercing-sucking: These forms of mouthparts have stylets, and are used to penetrate solid tissue and then suck up liquid food.
- Sponging: These forms of mouthparts are used to sponge and suck liquids and lack stylets (e.g. most DipteraDipteraDiptera , or true flies, is the order of insects possessing only a single pair of wings on the mesothorax; the metathorax bears a pair of drumstick like structures called the halteres, the remnants of the hind wings. It is a large order, containing an estimated 240,000 species, although under half...
).
- Siphoning: These forms of mouthparts lack stylets and are used to suck liquids, which are commonly found among species of LepidopteraLepidopteraLepidoptera is a large order of insects that includes moths and butterflies . It is one of the most widespread and widely recognizable insect orders in the world, encompassing moths and the three superfamilies of butterflies, skipper butterflies, and moth-butterflies...
.
Mouthparts that are mandibular are found in species of Odonata
Odonata
Odonata is an order of insects, encompassing dragonflies and damselflies . The word dragonfly is also sometimes used to refer to all Odonata, but the back-formation odonate is a more correct English name for the group as a whole...
, Isoptera, adult Neuroptera
Neuroptera
The insect order Neuroptera, or net-winged insects, includes the lacewings, mantidflies, antlions, and their relatives. The order contains some 6,010 species...
, Coleoptera, Hymenoptera
Hymenoptera
Hymenoptera is one of the largest orders of insects, comprising the sawflies, wasps, bees and ants. There are over 130,000 recognized species, with many more remaining to be described. The name refers to the heavy wings of the insects, and is derived from the Ancient Greek ὑμήν : membrane and...
, Blattaria, Orthoptera
Orthoptera
Orthoptera is an order of insects with paurometabolous or incomplete metamorphosis, including the grasshoppers, crickets and locusts.Many insects in this order produce sound by rubbing their wings against each other or their legs, the wings or legs containing rows of corrugated bumps...
, and Lepidoptera
Lepidoptera
Lepidoptera is a large order of insects that includes moths and butterflies . It is one of the most widespread and widely recognizable insect orders in the world, encompassing moths and the three superfamilies of butterflies, skipper butterflies, and moth-butterflies...
. However most adult Lepidoptera have siphoning mouthparts, while the larvae (commonly called caterpillar
Caterpillar
Caterpillars are the larval form of members of the order Lepidoptera . They are mostly herbivorous in food habit, although some species are insectivorous. Caterpillars are voracious feeders and many of them are considered to be pests in agriculture...
s) are the ones with the mandibles.
Mandibulate
The labrum
Labrum (arthropod mouthpart)
The labrum is a flap-like structure that lies immediately in front of the mouth in almost all extant euarthropods, the general exception being provided by the probable chelicerate-relatives the pycnogonids. It has proved to be by far the most controversial of all arthropod head structures. It is...
is a broad lobe forming the roof of the preoral cavity, suspended from the clypeus in front of the mouth and forming the upper lip. On its inner side it is membranous and may be produced into a median lobe, the epipharynx, bearing some sensilla
Sensilla
A sensillum is an insect sensory organ protruding from the cuticle, or sometime lying within or beneath it. Sensilla are divided in chemical, mechanical , thermal and visual....
. The labrum is raised away from the mandibles by two muscles arising in the head and inserted medially into the anterior margin of the labrum. It is closed against the mandibles in part by two muscles arising in the head and inserted on the posterior lateral margins on two small sclerites, the tormae, and, at least in some insects, by a resilin spring in the cuticle at the junction of the labrum with the clypeus. Differential use of the muscles. Until recently, the labrum generally was considered to be associated with first head segment. However recent studies of the embryology, gene expression, and nerve supply to the labrum show that it is innervated by the tritocerebrum of the brain, which is the fused ganglia of the third head segment. This is formed from fusion of parts of a pair of ancestral appendages found on the third head segment, showing their relation. Its ventral, or inner, surface is usually membranous and forms the lobe-like epipharynx, which bears mechanosensilla and chemosensilla.
Chewing insects have two mandibles, one on each side of the head. The mandibles are positioned between the labrum and maxillae. The mandibles cut and crush food and may be used for defense; generally they have an apical cutting edge and the more basal molar area grinds the food. They can be extremely hard (approximately 3 on Moh’s scale of mineral hardness
Mohs scale of mineral hardness
The Mohs scale of mineral hardness characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer material. It was created in 1812 by the German geologist and mineralogist Friedrich Mohs and is one of several definitions of hardness in...
, or an indentation hardness of about 30 kg mm−2) and thus many termites and beetles have no physical difficulty in boring through foils made from such common metals as copper, lead, tin, and zinc. The cutting edges are typically strengthened by the addition of zinc, manganese or, rarely, iron, in amounts up to about 4% of the dry weight. They are typically the largest mouthparts of chewing insects, being used to masticate (cut, tear, crush, chew) food items. They open outwards (to the sides of the head) and come together medially. In carnivorous chewing insects, the mandibles can be modified to be more knife-like, whereas in herbivorous chewing insects, they are more typically broad and flat on their opposing faces (e.g., caterpillar
Caterpillar
Caterpillars are the larval form of members of the order Lepidoptera . They are mostly herbivorous in food habit, although some species are insectivorous. Caterpillars are voracious feeders and many of them are considered to be pests in agriculture...
s). In male stag beetle
Stag beetle
Stag beetles are a group of about 1,200 species of beetle in the family Lucanidae, presently classified in four subfamilies Some species grow up to over 12 cm , but most are about 5 cm .-Overview:...
s, the mandibles are modified to such an extent that they do not serve any feeding function, but are instead used to defend mating sites from other males. In ant
Ant
Ants are social insects of the family Formicidae and, along with the related wasps and bees, belong to the order Hymenoptera. Ants evolved from wasp-like ancestors in the mid-Cretaceous period between 110 and 130 million years ago and diversified after the rise of flowering plants. More than...
s, the mandibles also serve a defensive function (particularly in soldier castes). In bull ants
Myrmecia
Myrmecia, often called bulldog ants, bull ants, inch ants, sergeant ants, jumper ants or jack-jumpers , is a genus of ants. Bull ants can grow to over in length, with the smallest species long...
, the mandibles are elongate and toothed, used as hunting (and defensive) appendages.
Situated beneath the mandibles, paired maxilla
Maxilla
The maxilla is a fusion of two bones along the palatal fissure that form the upper jaw. This is similar to the mandible , which is also a fusion of two halves at the mental symphysis. Sometimes The maxilla (plural: maxillae) is a fusion of two bones along the palatal fissure that form the upper...
e manipulate food during mastication
Mastication
Mastication or chewing is the process by which food is crushed and ground by teeth. It is the first step of digestion and it increases the surface area of foods to allow more efficient break down by enzymes. During the mastication process, the food is positioned between the teeth for grinding by...
. Maxillae can have hairs and "teeth" along their inner margins. At the outer margin, the galea
Galea
Galea may refer to:*Galea , ancient Roman helmet*Galea , a genus of rodents*Galea , part of the maxilla in the mouthparts of insects*Galea, a clade of sharks*Galea , a boat whose shape was used in galley division...
is a cupped or scoop-like structure, which sits over the outer edge of the labium. They also have palps, which are used to sense the characteristics of potential foods. The maxillae occupy a lateral position, one on each side of the head behind the mandibles. The proximal part of the maxilla consists of a basal cardo, which has a single articulation with the head, and a flat plate, the stipes, hinged to the cardo
Cardo
The cardo was a north-south oriented street in Roman cities, military camps, and coloniae. The cardo, an integral component of city planning, was lined with shops and vendors, and served as a hub of economic life. The main cardo was called cardo maximus.Most Roman cities also had a Decumanus...
. Both cardo and stipes are loosely joined to the head by membrane so that they are capable of movement. Distally on the stipes are two lobes, an inner lacinea and an outer galea, one or both of which may be absent. More laterally on the stipes is a jointed, leglike palp made up of a number of segments; in Orthoptera there are five. Anterior and posterior rotator muscles are inserted on the cardo, and ventral adductor muscles arising on the tentorium are inserted on both cardo and stipes. Arising in the stipes are flexor muscles of lacinea and galea and another lacineal flexor arises in the cranium, but neither lacinea nor galea has an extensor muscle. The palp has levator and depressor muscles arising in the stipes and each segment of the palp has a single muscle causing flexing of the next segment.
In mandibulate mouthparts, the labium
Labium
The labia are anatomical structures that are part of the female genitalia; they are the major externally visible portions of the vulva. In humans, there are two pairs of labia: the outer labia, or labia majora are larger and fattier, while the labia minora are folds of skin often concealed within...
is a quadrupedal structure, although it is formed from two fused secondary maxillae. It can be described as the floor of the mouth. With the maxillae, it assists manipulation of food during mastication
Mastication
Mastication or chewing is the process by which food is crushed and ground by teeth. It is the first step of digestion and it increases the surface area of foods to allow more efficient break down by enzymes. During the mastication process, the food is positioned between the teeth for grinding by...
or chewing or, in the unusual case of the dragonfly nymph, extends out to snatch prey back to the head where mandibles can eat it. The labium is similar in structure to the maxilla
Maxilla
The maxilla is a fusion of two bones along the palatal fissure that form the upper jaw. This is similar to the mandible , which is also a fusion of two halves at the mental symphysis. Sometimes The maxilla (plural: maxillae) is a fusion of two bones along the palatal fissure that form the upper...
e, but with the appendages of the two sides fused by the midline, so that they come to form a median plate. The basal part of the labium, equivalent to the maxillary cardines and possibly including a part of the sternum of the labial segment, is called the postmentum. This may be subdivided into a proximal submentum and a distal mentum. Distal to the postmentum, and equivalent to the fused maxillary stipites, is the prementum. The prementum closes the pre-oral cavity from behind. Terminally it bears four lobes, two inner glossae and two outer paraglossae, which are collectively known as the ligula. One or both pairs of lobes may be absent or they may be fused to form a single median process. A palp arises from each side of the prementum, often being three segmented.
The hypopharynx is a median lobe immediately behind the mouth, projecting forwards from the back of the preoral cavity, is a lobe of uncertain origin, but perhaps associated with the mandibular segment; in apterygotes, earwigs, and nymphal mayflies the hypopharynx bears a pair of lateral lobes, the superlinguae (singular: superlingua). It divides the cavity into a dorsal food pouch, or cibarium, and a ventral salivarium into which the salivary duct opens. Though, it is commonly found fused to the libium. Most of the hypopharynx is membranous, but the adoral face is sclerotized distally, and proximally contains a pair of suspensory sclerites which extend upwards to end in the lateral wall of the stomodeum. Muscles arising on the frons are inserted into these sclerites, which distally are hinged to a pair of lingual sclerites. These, in turn, have inserted into them antagonistic pairs of muscles arising on the tentorium and labium. The various muscles serve to swing the hypopharynx forwards and back, and in the cockroach there are two more muscles running across the hypopharynx which dilate the salivary orifice and expand the salivarium.
Piercing-sucking
Some mouthparts have adapted special piercing parts along with the already sponging ones, used to pierce through tissues of plants and animals. Mosquitoes are infamous for being hemophagous (feeding on blood) pest of people as the female pierces the skin (which could spread disease). The parts of mosquito proboscis are the paired mandibles and maxillae that form needle-like structures, called stylet
Stylet
A stylet is a hard, sharp, anatomical structure found in some invertebrates.For example, the word stylet or stomatostyle, is used for the primitive piercing mouthparts of some nematodes and some nemerteans...
s, which are enclosed by the labium. When mosquito bites, maxillae penetrate the skin and anchor the mouthparts thus allowing other parts to be inserted. The sheath-like labium slides back and the remaining mouthparts pass through its tip and into the tissue. Then through hypopharynx mosquito injects saliva
Saliva
Saliva , referred to in various contexts as spit, spittle, drivel, drool, or slobber, is the watery substance produced in the mouths of humans and most other animals. Saliva is a component of oral fluid. In mammals, saliva is produced in and secreted from the three pairs of major salivary glands,...
, which contains anticoagulants that stop the blood from clotting. And finally the labrum (upper lip) is used to suck up the blood. Species of the genus Anopheles are characterized by their long palpi (two parts with widening end), almost reaching the end of labrum.
Siphoning
The proboscis
Proboscis
A proboscis is an elongated appendage from the head of an animal, either a vertebrate or an invertebrate. In simpler terms, a proboscis is the straw-like mouth found in several varieties of species.-Etymology:...
(plural – probosces) is formed from maxillary galeae and is adaption found in some insects for sucking. The muscles of the cibarium or pharynx are strongly developed which form the pump. In Hemiptera and many Diptera, which feed on fluids within plants or animals, some components of the mouthparts are modified for piercing, and the elongate structures are called stylets. The combined tubular structures are referred to as the proboscis, although specialized terminology is used in some groups.
In species of Lepidoptera
Lepidoptera
Lepidoptera is a large order of insects that includes moths and butterflies . It is one of the most widespread and widely recognizable insect orders in the world, encompassing moths and the three superfamilies of butterflies, skipper butterflies, and moth-butterflies...
(i.e. Butterflies and moths), it consists of two tubes held together by hooks and separable for cleaning. Each tube is inwardly concave, thus forming a central tube up which moisture is sucked. Suction is effected through the contraction and expansion of a sac in the head. The proboscis is coiled under the head when the insect is at rest and extended only when feeding. The maxillary palpi are reduced and even vestigial. They are conspicuous and 5-segmented in some of the more basal families and are often folded. The shape and dimensions of the proboscis have evolved to give different species a wider and therefore more advantageous diet. There is an allometric scaling relationship between body mass of Lepidoptera and length of proboscis from which an interesting adaptive departure is the unusually long-tongued hawk moth Xanthopan morgani praedicta
Xanthopan morgani
Xanthopan morgani, or Morgan's Sphinx, is a very large hawk moth from West Africa and Madagascar. It is the sole member of its genus, and little is known of the biology, though the adults have been found to visit orchids .In January 1862 while researching insect pollination of orchids, Charles...
. Charles Darwin
Charles Darwin
Charles Robert Darwin FRS was an English naturalist. He established that all species of life have descended over time from common ancestry, and proposed the scientific theory that this branching pattern of evolution resulted from a process that he called natural selection.He published his theory...
predicted the existence and proboscis length of this moth before its discovery based on his knowledge of the long-spurred Madagascan star orchid Angraecum sesquipedale
Angraecum sesquipedale
Angraecum sesquipedale is an epiphytic orchid in the genus Angraecum that is endemic to Madagascar. The orchid was first discovered by the French botanist Louis-Marie Aubert du Petit-Thouars in 1798, but was not described until 1822...
.
Sponging
The mouthparts of insects which feed on fluids are modified in various ways to form a tube through which liquid can be drawn into the mouth and usually another through which saliva passes. The muscles of the cibarium or pharynx are strongly developed to form a pump. In non-biting flies the mandibles are absent and other structures are reduced; the labial palps have become modified to form the labellum and the maxillary palps are present, although sometimes short. In Brachycera, the labellum is especially prominent and used for sponging liquid or semi-liquid food. The labella is a complex structure consisting of many grooves, called pseudotrachea, which sops up liquids. Salivary secretions from the labella assist in dissolving and collecting food particles so that they may be more easily taken up by the pseudotrachea, this is thought to occur by capillary action. The liquid food is then drawn up from the pseudotracheae through the food channel into the esophagus
Esophagus
The esophagus is an organ in vertebrates which consists of a muscular tube through which food passes from the pharynx to the stomach. During swallowing, food passes from the mouth through the pharynx into the esophagus and travels via peristalsis to the stomach...
.
The mouthparts of bee
Bee
Bees are flying insects closely related to wasps and ants, and are known for their role in pollination and for producing honey and beeswax. Bees are a monophyletic lineage within the superfamily Apoidea, presently classified by the unranked taxon name Anthophila...
s are of a chewing and lapping-sucking type. Lapping is a mode of feeding in which liquid or semi-liquid food adhering to a protrusible organ, or “tongue”, is transferred from substrate to mouth. In the honey bee
Honey bee
Honey bees are a subset of bees in the genus Apis, primarily distinguished by the production and storage of honey and the construction of perennial, colonial nests out of wax. Honey bees are the only extant members of the tribe Apini, all in the genus Apis...
(Hymenoptera
Hymenoptera
Hymenoptera is one of the largest orders of insects, comprising the sawflies, wasps, bees and ants. There are over 130,000 recognized species, with many more remaining to be described. The name refers to the heavy wings of the insects, and is derived from the Ancient Greek ὑμήν : membrane and...
: Apidae
Apidae
The Apidae are a large family of bees, comprising the common honey bees, stingless bees , carpenter bees, orchid bees, cuckoo bees, bumblebees, and various other less well-known groups...
: Apis mellifera), the elongate and fused labial glossae form a hairy tongue, which is surrounded by the maxillary galeae and the labial palps to form a tubular proboscis containing a food canal. In feeding, the tongue is dipped into the nectar or honey, which adheres to the hairs, and then is retracted so that adhering liquid is carried into the space between the galeae and labial palps. This back-and-forth glossal movement occurs repeatedly. Movement of liquid to the mouth apparently results from the action of the cibarial pump, facilitated by each retraction of the tongue pushing liquid up the food canal.
Thorax
The insect thorax has three segments: The prothoraxProthorax
The prothorax is the foremost of the three segments in the thorax of an insect, and bears the first pair of legs. Its principal sclerites are the pronotum , the prosternum , and the propleuron on each side. The prothorax never bears wings in extant insects, though some fossil groups possessed...
, mesothorax
Mesothorax
The mesothorax is the middle of the three segments in the thorax of an insect, and bears the second pair of legs. Its principal sclerites are the mesonotum , the mesosternum , and the mesopleuron on each side...
, and the metathorax
Metathorax
The metathorax is the posterior of the three segments in the thorax of an insect, and bears the third pair of legs. Its principal sclerites are the metanotum , the metasternum , and the metapleuron on each side...
. The anterior segment, closest to the head, is the prothorax, with the major features being the first pair of legs and the pronotum. The middle segment is the mesothorax with the major features being the second pair of legs and the anterior wings. The third and most posterior segment, abutting the abdomen, is the metathorax, which features the third pair of legs and the posterior wings. Each segment is dilineated by an intersegmental suture. Each segment has four basic regions. The dorsal surface is called the tergum (or notum) to distinguish them from the abdominal terga. The two lateral regions are called the pleura (singular: pleuron) and the ventral aspect is called the sternum. In turn, the notum of the prothorax is called the pronotum, the notum for the mesothorax is called the mesonotum and the notum for the metathorax is called the metanotum. Continuing with this logic, there is also the mesopleura and metapleura as well as the mesosternum and metasternum.
The tergal plates of the thorax are simple structures in apterygotes and in many immature insects, but are variously modified in winged adults. The pterothoracic nota each have two main divisions: the anterior wing-bearing alinotum and the posterior phragma-bearing postnotum. Phragmata (singular: phragma) are plate-like apodemes that extend inwards below the antecostal sutures, marking the primary intersegmental folds between segments; phragmata provide attachment for the longitudinal flight muscles. Each alinotum (sometimes confusingly referred to as a “notum”) may be traversed by sutures that mark the position of internal strengthening ridges and commonly divide the plate into three areas: the anterior prescutum, the scutum, and the smaller posterior scutellum. The lateral pleural sclerites are believed to be derived from the subcoxal segment of the ancestral insect leg. These sclerites may be separate, as in silverfish, or fused into an almost continuous sclerotic area, as in most winged insects.
Prothorax
The prothorax on this conehead is shielded by a large pronotum that extends from over the cervix (neck) on the anterior side to cover the mesothorax and most of the metathorax on the posterior side, as well as covering the pleura on the prothorax. The pronotum of the prothorax may be simple in structure and small in comparison with the other nota, but in beetles, mantids, many bugs, and some Orthoptera the pronotum is expanded and in cockroaches it forms a shield that covers part of the head and mesothorax.Pterothorax
Because the mesothorax and metathorax hold the wings, they have a combined name called the pterothorax (pteron = wing). The forewings, which goes by different names in different orders (e.g., the tegmina in OrthopteraOrthoptera
Orthoptera is an order of insects with paurometabolous or incomplete metamorphosis, including the grasshoppers, crickets and locusts.Many insects in this order produce sound by rubbing their wings against each other or their legs, the wings or legs containing rows of corrugated bumps...
and elytra in Coleoptera), arise between the mesonotum and the mesopleura, and the hindwings articulate between the metanotum and metapleura. The mesopleura and metapleura are where the legs arise from. The mesothorax and metathorax each have a pleural suture (mesopleural and metapleural sutures) that runs from the wing base to the coxa of the leg. The sclerite anterior to the pleural suture is called the episternum (serially, the mesepisternum and metepisternum). The sclerite posterior to the suture is called the epimiron (serially, the mesepimiron and metepimiron). Spiracles, the external organs of the respiratory system, are found on the pterothorax, usually one between the pro- and mesopleoron as well as one between the meso- and metapleuron.
The ventral view or sternum follows the same convention, with the prosternum under the prothorax, the mesosternum under the mesothorax and the metasternum under the metathorax. The notum, pleura and sternum of each segment have a variety of different sclerites and sutures which vary greatly from order to order, and they will not be discussed in detail in this section.
Wings
Most phylogenetically advanced insects have two pairs of wingsInsect wing
Insects are the only group of invertebrates known to have evolved flight. Insects possess some remarkable flight characteristics and abilities, still far superior to attempts by humans to replicate their capabilities. Even our understanding of the aerodynamics of flexible, flapping wings and how...
located on the second and third thoracic segments. Insects are the only invertebrate
Invertebrate
An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...
s to have developed flight capability, and this has played an important part in their success. Insect flight
Insect flight
Insects are the only group of invertebrates known to have evolved flight. Insects possess some remarkable flight characteristics and abilities, still far superior to attempts by humans to replicate their capabilities. Even our understanding of the aerodynamics of flexible, flapping wings and how...
is not very well understood, relying heavily on turbulent aerodynamic effects. The primitive insect groups use muscles that act directly on the wing structure. The more advanced groups making up the Neoptera
Neoptera
Neoptera is a classification group that includes almost all the winged insects, specifically those that can flex their wings over their abdomens...
have foldable wings and their muscles act on the thorax wall and power the wings indirectly. These muscles are able to contract multiple times for each single nerve impulse, allowing the wings to beat faster than would ordinarily be possible.
Insect flight can be extremely fast, maneuverable and versatile. This flight is possible due to the changing shape, extraordinary control and variable motion of the insect wing. Insect orders use different flight mechanisms, for example, the flight of a butterfly can be explained using steady-state, non-transitory aerodynamics
Aerodynamics
Aerodynamics is a branch of dynamics concerned with studying the motion of air, particularly when it interacts with a moving object. Aerodynamics is a subfield of fluid dynamics and gas dynamics, with much theory shared between them. Aerodynamics is often used synonymously with gas dynamics, with...
and thin aerofoil
Airfoil
An airfoil or aerofoil is the shape of a wing or blade or sail as seen in cross-section....
theory. For a more detailed description, see insect flight
Insect flight
Insects are the only group of invertebrates known to have evolved flight. Insects possess some remarkable flight characteristics and abilities, still far superior to attempts by humans to replicate their capabilities. Even our understanding of the aerodynamics of flexible, flapping wings and how...
.
Internal
Each of the wings consists of a thin membrane supported by a system of veins. The membrane is formed by two layers of integument closely apposed, while the veins are formed where the two layers remain separate and the cuticle may be thicker and more heavily sclerotized. Within each of the major veins is a nerve and a trachea, and, since the cavities of the veins are connected with the hemocoel, hemolymph can flow into the wings. Also are the wings lumen, being an extension of the hemocoel, which contains the tracheae, nerves, and hemolymph. As the wing develops, the dorsal and ventral integumental layers become closely apposed over most of their area forming the wing membrane. The remaining areas form channels, the future veins, in which the nerves and tracheae may occur. The cuticle surrounding the veins becomes thickened and more heavily sclerotized to provide strength and rigidity to the wing. Hairs of two types may occur on the wings: microtrichia, which are small and irregularly scattered, and macrotrichia, which are larger, socketed, and may be restricted to veins. The scales of Lepidoptera and Trichoptera are highly modified macrotrichia.
Veins
In some very small insects, the venation may be greatly reduced. In Chalcidoidea (Chalcid wasps), for instance, only the subcosta and part of the radius are present. Conversely, an increase in venation may occur by the branching of existing veins to produce accessory veins or by the development of additional, intercalary veins between the original ones, as in the wings of Orthoptera
Orthoptera
Orthoptera is an order of insects with paurometabolous or incomplete metamorphosis, including the grasshoppers, crickets and locusts.Many insects in this order produce sound by rubbing their wings against each other or their legs, the wings or legs containing rows of corrugated bumps...
(Grasshoppers and crickets). Large numbers of cross-veins are present in some insects, and they may form a reticulum as in the wings of Odonata
Odonata
Odonata is an order of insects, encompassing dragonflies and damselflies . The word dragonfly is also sometimes used to refer to all Odonata, but the back-formation odonate is a more correct English name for the group as a whole...
(Dragonflies and damselflies) and at the base of the forewings of Tettigonioidea and Acridoidea
Acridoidea
Acridoidea is a superfamily of grasshoppers including locusts in the order Orthoptera.-Classification:*Acrididae MacLeay, 1821*Catantopidae*Charilaidae Dirsh, 1953*Dericorythidae Jacobson & Bianchi, 1902–1905*Lathiceridae Dirsh, 1954...
(Katydids and grasshoppers respectively).
The archedictyon is the name given to a hypothetical scheme of wing venation proposed for the very first winged insect. It is based on a combination of speculation and fossil data. Since all winged insects are believed to have evolved from a common ancestor, the archediction represents the "template" that has been modified (and streamlined) by natural selection for 200 million years. According to current dogma, the archedictyon contained 6-8 longitudinal veins. These veins (and their branches) are named according to a system devised by John Comstock and George Needham—the Comstock-Needham System:
- Costa (C) - the leading edge of the wing
- Subcosta (Sc) - second longitudinal vein (behind the costa), typically unbranched
- Radius (R) - third longitudinal vein, one to five branches reach the wing margin
- Media (M) - fourth longitudinal vein, one to four branches reach the wing margin
- Cubitus (Cu) - fifth longitudinal vein, one to three branches reach the wing margin
- Anal veins (A1, A2, A3) - unbranched veins behind the cubitus
The costa (C) is the leading marginal vein on most insects, although sometimes there is a small vein above the cost called the precosta, although in almost all extant insects, the precosta is fused with the costa; The costa rarely ever branch because is at the leading edge, which is associated at its base with the humeral plate. The trachea of the costal vein is perhaps a branch of the subcostal trachea. Located after the costa is the third vein, the subcosta, which branches into two two separate veins: the anterior and posterior. The base of the subcosta is associated with the distal end of the neck of the first axillary (see section below). The fourth vein is the radius (R), which is branched into five separate veins. The radius is generally the strongest vein of the wing. Toward the middle of the wing it forks into a first undivided branch (R1) and a second branch, called the radial sector (Ra), which subdivides dichotomously into four distal branches (R2, R3, R4, R5). Basally the radius is flexibly united with the anterior end of the second axillary (2Ax).
The fifth vein of the wing is the media. In the archetype pattern (A) the media forks into two main branches, a media anterior (MA), which divides into two distal branches (MA1, MA2), and a median sector, or media posterior (MP), which has four terminal branches (M1, M2, M3, M4). In most modern insects the media anterior has been lost, and the usual "media" is the four-branched media posterior with the common basal stem. In the Ephemerida, according to present interpretations of the wing venation, both branches of the media are retained, while in Odonata the persisting media is the primitive anterior branch. The stem of the media is often united with the radius, but when it occurs as a distinct vein its base is associated with the distal median plate (m') or is continuously sclerotized with the latter. The cubitus, the sixth vein of the wing, is primarily two branched. The primary forking of the takes place near the base of the wing, forming the two principal branches (Cu1, Cu2). The anterior branch may break up into a number of secondary branches, but commonly it forks into two distal branches. The second branch of the cubitus (Cu2) in Hymenoptera, Trichoptera, and Lepidoptera was mistaken by Comstock and Needham for the first anal. Proximally the main stem of the cubitus is associated with the distal median plate (m') of the wing base.
Postcubitus (Pcu) is the first anal of the Comstock and Needham system. The Postcubitus, however, has the status of an independent wing vein and should be recognized as such. In nymphal wings, its trachea arises between the cubital trachea and the group of vannal tracheae. In the mature wings of more generalized insect the Postcubitus is always associated proximally with the cubitus and is never intimately connected with the flexor sclerite (3Ax) of the wing base. In Neuroptera, Mecoptera, and Trichoptera the postcubitus may be more closely associated with the vannal veins, but its base is always free from the latter. The postcubitus is usually unbranched; it is primitively two branched. The vannal veins (lV to nV) are the anal veins that are immediately associated with the third axillary, and which are directly affected by the movement of this sclerite that brings about the flexion of the wings. In number the vannal veins vary. from 1 to 12, according to the expansion of the vannal area of the wing. The vannal tracheae usually arise from a common tracheal stem in nymphal insects, and the veins are regarded as branches of a single anal vein. Distally the vannal veins are either simple or branched. Jugal Veins (J) of the jugal lobe of the wing is often occupied by a network of irregular veins, or it may be entirely membranous; but sometimes it contains one or two distinct small veins, the first jugal vein, or vena arcuata, and the second jugal vein, or vena cardinalis (2J).
- C-Sc cross-veins - run between the costa and subcosta
- R cross-veins - run between adjacent branches of the radius
- R-M cross-veins - run between the radius and media
- M-Cu cross-veins - run between the media and cubitus
All the veins of the wing are subject to secondary forking and to union by cross-veins. In some orders of insects the cross-veins are so numerous that the whole venational pattern becomes a close network of branching veins and cross-veins. Ordinarily, however, there is a definite number of cross-veins having specific locations. The more constant cross-veins are the humeral cross-vein (h) between costa and subcosta, the radial cross-vein (r) between R and the first fork of Rs, the sectorial cross-vein (s) between the two forks of R8, the median cross-vein (m-m) between M2 and M3, and the mediocubital cross-vein (m-cu) between media and cubitus.
The veins of insect wings are characterized by a convex-concave placement, such as those seen in mayflies (i.e., concave is "down" and convex is "up") which alternate regularly and by their branching; whenever a vein forks there is always an interpolated vein of the opposite position between the two branches. The a concave vein will fork into two concave veins (with the interpolated vein being convex) and the regular alteration of the veins is preserved. The veins of the wing appear to fall into an undulating according to whether they have a tendency to fold up or down when the wing is relaxed. The basal shafts of the veins are convex, but each vein forks distally into an anterior convex branch and a posterior concave branch. Thus the costa and subcosta are regarded as convex and concave branches of a primary first vein, Rs is the concave branch of the radius, posterior media the concave branch of the media, Cu1 and Cu2 are respectively convex and concave, while the primitive Postcubitus and the first vannal have each an anterior convex branch and a posterior concave branch. The convex or concave nature of the veins has been used as evidence in determining the identities of the persisting distal branches of the veins of modern insects, but it has not been demonstrated to be consistent for all wings.
Fields
Wing areas are delimited and subdivided by fold-lines, along which the wings can fold. Along with the flexion-lines, at which flexes during flight. Between the flexion-lines and the fold-lines, the fundamental distinction is often blurred, as fold-lines may permit some flexibility or vice-versa. Two constants that are found in nearly all insect wings are the claval (a flexion-line) and jugal folds (or fold line); forming variable and unsatisfactory boundaries. Wing foldings can very complicated, with transverse folding occurs in the hind wings of Dermaptera and Coleoptera, and in some insects the anal area can be folded like a fan.
There are about four different fields found on the insect wings:
- Remigium
- Anal area (vannus)
- Jugal area
- Axillary area
- Alula
Most veins and crossveins occur in the anterior area of the remigium, which is responsible for most of the flight, powered by the thoracic muscles. The posterior portion of the remigium is sometimes called the clavus; the two other posterior fields are the anal and jugal areas. When the vannal fold has the usual position anterior to the group of anal veins, the remigium contains the costal, subcostal, radial, medial, cubital, and postcubital veins. In the flexed wing the remigium turns posteriorly on the flexible basal connection of the radius with the second axillary, and the base of the mediocubital field is folded medially on the axillary region along the plica basalis (bf) between the median plates (m, m') of the wing base.
The vannus is bordered by the vannal fold, which typically occurs between the postcubitus and the first vannal vein. In Orthoptera it usually has this position. In the forewing of Blattidae, however, the only fold in this part of the wing lies immediately before the postcubitus. In Plecoptera the vannal fold is posterior to the postcubitus, but proximally it crosses the base of the first vannal vein. In the cicada the vannal fold lies immediately behind the first vannal vein (lV). These small variations in the actual position of the vannal fold, however, do not affect the unity of action of the vannal veins, controlled by the flexor sclerite (3Ax), in the flexion of the wing. In the hind wings of most Orthoptera a secondary vena dividens forms a rib in the vannal fold. The vannus is usually triangular in shape, and its veins typically spread out from the third axillary like the ribs of a fan. Some of the vannal veins may be branched, and secondary veins may alternate with the primary veins. The vannal region is usually best developed in the hind wing, in which it may be enlarged to form a sustaining surface, as in Plecoptera and Orthoptera. The great fanlike expansions of the hind wings of Acrididae are clearly the vannal regions, since their veins are all supported on the third axillary sclerites on the wing bases, though Martynov (1925) ascribes most of the fan areas in Acrididae to the jugal regions of the wings. The true jugum of the acridid wing is represented only by the small membrane (Ju) mesad of the last vannal vein. The jugum is more highly developed in some other Orthoptera, as in the Mantidae. In most of the higher insects with narrow wings the vannus becomes reduced, and the vannal fold is lost, but even in such cases the flexed wing may bend along a line between the postcubitus and the first vannal vein.
The Jugal Region, or Neala, is a region of the wing that is usually a small membranous area proximal to the base of the vannus strengthened by a few small, irregular veinlike thickenings; but when well developed it is a distinct section of the wing and may contain one or two jugal veins. When the jugal area of the forewing is developed as a free lobe, it projects beneath the humeral angle of the hind wing and thus serves to yoke the two wings together. In the Jugatae group of Lepidoptera it bears a long finger-like lobe. The jugal region was termed the neala ("new wing") because it is evidently a secondary and recently developed part of the wing.
The axilary region is region containing the axillary sclerites has in general the form of a scalene triangle. The base of the triangle (a-b) is the hinge of the wing with the body; the apex (c) is the distal end of the third axillary sclerite; the longer side is anterior to the apex. The point d on the anterior side of the triangle marks the articulation of the radial vein with the second axillary sclerite. The line between d and c is the plica basalis (bf), or fold of the wing at the base of the mediocubital field.
At the posterior angle of the wing base in some Diptera there is a pair of membranous lobes (squamae, or calypteres) known as the alula. The alula is well developed in the house fly. The outer squama (c) arises from the wing base behind the third axillary sclerite (3Ax) and evidently represents the jugal lobe of other insects (A, D); the larger inner squama (d) arises from the posterior scutellar margin of the tergum of the wing-bearing segment and forms a protective, hoodlike canopy over the halter. In the flexed wing the outer squama of the alula is turned upside down above the inner squama, the latter not being affected by the movement of the wing. In many Diptera a deep incision of the anal area of the wing membrane behind the single vannal vein sets off a proximal alar lobe distal to the outer squama of the alula.
Joints
The various movements of the wings, especially in insects that flex the wings horizontally over the back when at rest, of which demand a more complicated articular structure at the wing base than a mere hinge of the wing with the body. Each wing is attached to the body by a membranous basal area, but the articular membrane contains a number of small articular sclerites, collectively known as the pteralia. The pteralia include an anterior humeral plate at the base of the costal vein, a group of axillaries (Ax) associated with the subcostal, radial, and vannal veins, and two less definite median plates (m, m') at the base of the mediocubital area. The axillaries are specifically developed only in the wing-flexing insects, where they constitute the flexor mechanism of the wing operated by the flexor muscle arising on the pleuron. Characteristic of the wing base is also a small lobe on the anterior margin of the articular area proximal to the humeral plate, which, in the forewing of some insects, is developed into a large, flat, scale-like flap, the tegula, overlapping the base of the wing. Posteriorly the articular membrane often forms an ample lobe between the wing and the body, and its margin is generally thickened and corrugated, giving the appearance of a ligament, the so-called axillary cord, continuous mesally with the posterior marginal scutellar fold of the tergal plate bearing the wing.
The articular sclerites, or pteralia, of the wing base of the wing-flexing insects and their relations to the body and the wing veins, shown diagrammatically, are as follows:
- Humeral plates
- First Axillary
- Second Axillary
- Third Axillary
- Fourth Axillary
- Median plates (m, m')
The humeral plate is usually a small sclerite on the anterior margin of the wing base, movable and articulated with the base of the costal vein. Odonata have their humeral plate grately enlargened, with two muscles arising from the episternum inserted into the Humeral plates and two from the edge of the epimeron inserted into the axillary plate.
The first axillary sclerite (lAx) is the anterior hinge plate of the wing base. Its anterior part is supported on the anterior notal wing process of the tergum (ANP); its posterior part articulates with the tergal margin. The anterior end of the sclerite is generally produced as a slender arm, the apex of which (e) is always associated with the base of the subcostal vein (Sc), though it is not united with the latter. The body of the sclerite articulates laterally with the second axillary. The second axillary sclerite (2Ax) is more variable in form than the first axillary, but its mechanical relations are no less definite. It is obliquely hinged to the outer margin of the body of the first axillary, and the radial vein (R) is always flexibly attached to its anterior end (d). The second axillary presents both a dorsal and a ventral sclerotization in the wing base; its ventral surface rests upon the fulcral wing process of the pleuron. The second axillary, therefore, is the pivotal sclerite of the wing base, and it specifically manipulates the radial vein.
The third axillary sclerite (3Ax) lies in the posterior part of the articular region of the wing. Its form is highly variable and often irregular, but the third axillary is the sclerite on which is inserted the flexor muscle of the wing (D). Mesally it articulates anteriorly (f) with the posterior end of the second axillary, and posteriorly (b) with the posterior wing process of the tergum (PNP), or with a small fourth axillary when the latter is present. Distally the third axillary is prolonged in a process which is always associated with the bases of the group of veins in the anal region of the wing here termed the vannal veins (V). The third axillary, therefore, is usually the posterior hinge plate of the wing base and is the active sclerite of the flexor mechanism, which directly manipulates the vannal veins. The contraction of the flexor muscle (D) revolves the third axillary on its mesal articulations (b, f) and thereby lifts its distal arm; this movement produces the flexion of the wing. The Fourth Axillary sclerite is not a constant element of the wing base. When present it is usually a small plate intervening between the third axillary and the posterior notal wing process and is probably a detached piece of the latter.
The median plates (m, m' are also sclerites that are not so definitely differentiated as specific plates as are the three principal axillaries, but nevertheless they are important elements of the flexor apparatus. They lie in the median area of the wing base distal to the second and third axillaries and are separated from each other by an oblique line (bf) which forms a prominent convex fold during flexion of the wing. The proximal plate (m) is usually attached to the distal arm of the third axillary and perhaps should be regarded as a part of the latter. The distal plate ( m') is less constantly present as a distinct sclerite and may be represented by a general sclerotization of the base of the mediocubital field of the wing. When the veins of this region are distinct at their bases, they are associated with the outer median plate.
Coupling, folding, and other features
In many insect species, the fore and hind wing are coupled together, which improves the aerodynamic efficiency of flight. The most common coupling mechanism (e.g., Hymenoptera
Hymenoptera
Hymenoptera is one of the largest orders of insects, comprising the sawflies, wasps, bees and ants. There are over 130,000 recognized species, with many more remaining to be described. The name refers to the heavy wings of the insects, and is derived from the Ancient Greek ὑμήν : membrane and...
and Trichoptera
Trichoptera
The caddisflies are an order, Trichoptera, of insects with approximately 12,000 described species. Also called sedge-flies or rail-flies, they are small moth-like insects having two pairs of hairy membranous wings...
) is a row of small hooks on the forward margin of the hind wing, or "hamuli", which lock onto the fore wing, keeping them held together (hamulate coupling). In some other insect species (e.g., Mecoptera
Mecoptera
Mecoptera are an order of insects with about 550 species in nine families worldwide. Mecoptera are sometimes called scorpionflies after their largest family, Panorpidae, in which the males have enlarged genitals that look similar to the stinger of a scorpion...
, Lepidoptera
Lepidoptera
Lepidoptera is a large order of insects that includes moths and butterflies . It is one of the most widespread and widely recognizable insect orders in the world, encompassing moths and the three superfamilies of butterflies, skipper butterflies, and moth-butterflies...
, and some Trichoptera
Trichoptera
The caddisflies are an order, Trichoptera, of insects with approximately 12,000 described species. Also called sedge-flies or rail-flies, they are small moth-like insects having two pairs of hairy membranous wings...
) the jugal lobe of the fore wing covers a portion of the hind wing (jugal coupling), or the margins of the fore and hind wing overlap broadly (amplexiform coupling), or the hindwing bristles, or frenulum, hook under the retaining structure or retinalucum on the forewing.
When at rest, the wings are held over the back in most insects, which may involve longitudinal folding of the wing membrane and sometimes also transverse folding. Folding may sometimes occur along the flexion lines. Though fold lines may be transverse, as in the hind wings of beetles and earwigs, they are normally radial to the base of the wing, allowing adjacent sections of a wing to be folded over or under each other. The commonest fold line is the jugal fold, situated just behind the third anal vein, although, most Neoptera have a jugal fold just behind vein 3A on the forewings. It is sometimes also present on the hindwings. Where the anal area of the hindwing is large, as in Orthoptera and Blattodea, the whole of this part may be folded under the anterior part of the wing along a vannal fold a little posterior to the claval furrow. In addition, in Orthoptera and Blattodea, the anal area is folded like a fan along the veins, the anal veins being convex, at the crests of the folds, and the accessory veins concave. Whereas the claval furrow and jugal fold are probably homologous in different species, the vannal fold varies in position in different taxa. Folding is produced by a muscle arising on the pleuron and inserted into the third axillary sclerite in such a waythat, when it contracts, the sclerite pivots about its points of articulation with the posterior notal process and the second axillary sclerite.
As a result, the distal arm of the third axillary sclerite rotates upwards and inwards, so that finally its position is completely reversed. The anal veins are articulated with this sclerite in such a way that when it moves they are carried with it and become flexed over the back of the insect. Activity of the same muscle in flight affects the power output of the wing and so it is also important in flight control. In orthopteroid insects, the elasticity of the cuticle causes the vannal area of the wing to fold along the veins. Consequently energy is expended in unfolding this region when the wings are moved to the flight position. In general, wing extension probably results from the contraction of muscles attached to the basalar sclerite or, in some insects, to the subalar sclerite.
Legs
The typical and usual segments of the insect leg are divided into the coxaCoxa
Coxa may refer to:* Theta Leonis, a star* Nickname of Brazilian soccer team Coritiba Foot Ball Club* Hip, below the lateral side of the abdomen* The short most-proximal base jointed segment of the arthropod leg...
, one trochanter, the femur
Femur
The femur , or thigh bone, is the most proximal bone of the leg in tetrapod vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs. In vertebrates with four legs such as dogs and horses, the femur is found only in...
, the tibia
Tibia
The tibia , shinbone, or shankbone is the larger and stronger of the two bones in the leg below the knee in vertebrates , and connects the knee with the ankle bones....
, the tarsus
Tarsus
Tarsus may refer to:*Tarsus , a cluster of articulating bones in each foot** Tarsometatarsus, a fusion of the tarsus and metatarsus mainly found in birds...
, and the pretarsus. The coxa in its more symmetrical form, has the shape of a short cylinder or truncate cone, though commonly it is ovate and may be almost spherical. The proximal end of the coxa is girdled by a submarginal basicostal suture which forms internally a ridge, or basicosta, and sets off a marginal flange, the coxomarginale, or basicoxite. The basicosta strengthens the base of the coxa and is commonly enlarged on the outer wall to give insertion to muscles ; on the mesal half of the coxa, however, it is usually weak and often confluent with the coxal margin. The trochanteral muscles that take their origin in the coxa are always attached distal to the basicosta. The coxa is attached to the body by an articular membrane, the coxal corium, which surrounds its base. These two articulations are perhaps the primary dorsal and ventral articular points of the subcoxo-coxal hinge. In addition, the insect coxa has often an anterior articulation with the anterior, ventral end of the trochantin, but the trochantinal articulation does not coexist with a sternal articulation. The pleural articular surface of the coxa is borne on a mesal inflection of the coxal wall. If the coxa is movable on the pleural articulation alone, the coxal articular surface is usually inflected to a sufficient depth to give a leverage to the abductor muscles inserted on the outer rim of the coxal base. Distally the coxa bears an anterior and a posterior articulation with the trochanter. The outer wall of the coxa is often marked by a suture extending from the base to the anterior trochanteral articulation. In some insects the coxal suture falls in line with the pleural suture, and in such cases the coxa appears to be divided into two parts corresponding to the episternum and epimeron of the pleuron. The coxal suture is absent in many insects.
The inflection of the coxal wall bearing the pleural articular surface divides the lateral wall of the basicoxite into a prearticular part and a postarticular part, and the two areas often appear as two marginal lobes on the base of the coxa. The posterior lobe is usually the larger and is termed the meron
Meron
A meron or half-instanton is a Euclidean space-time solution of the Yang-Mills field equations. It is a singular non-self-dual solution of topological charge 1/2. The instanton is believed to be composed of two merons....
. The meron may be greatly enlarged by an extension distally in the posterior wall of the coxa; in the Neuroptera, Mecoptera, Trichoptera, and Lepidoptera, the meron is so large that the coxa appears to be divided into an anterior piece, the so-called "coxa genuina," and the meron, but the meron never includes the region of the posterior trochanteral articulation, and the groove delimiting it is always a part of the basicostal suture. A coxa with an enlarged meron has an appearance similar to one divided by a coxal suture falling in line with the pleural suture, but the two conditions are fundamentally quite different and should not be confused. The meron reaches the extreme of its departure from the usual condition in the Diptera. In some of the more generalized flies, as in the Tipulidae, the meron of the middle leg appears as a large lobe of the coxa projecting upward and posteriorly from the coxal base; in higher members of the order it becomes completely separated from the coxa and forms a plate of the lateral wall of the mesothorax.
The trochanter is the basal segment of the telopodite; it is always a small segment in the insect leg, freely movable by a horizontal hinge on the coxa, but more or less fixed to the base of the femur. When movable on the femur the trochantero femoral hinge is usually vertical or oblique in a vertical plane, giving a slight movement of production and reduction at the joint, though only a reductor muscle is present. In the Odonata, both nymphs and adults, there are two trochanteral segments, but they are not movable on each other; the second contains the reductor muscle of the femur. The usual single trochanteral segment of insects, therefore, probably represents the two trochanters of other arthropods fused into one apparent segment, since it is not likely that the primary coxotrochanteral hinge has been lost from the leg. In some of the Hymenoptera a basal subdivision of the femur simulates a second trochanter, but the insertion of the reductor muscle on its base attests that it belongs to the femoral segment, since as shown in the odonate leg, the reductor has its origin in the true second trochanter.
The femur
Femur
The femur , or thigh bone, is the most proximal bone of the leg in tetrapod vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs. In vertebrates with four legs such as dogs and horses, the femur is found only in...
is the third segment of the insect leg, is usually the longest and strongest part of the limb, but it varies in size from the huge hind femur of leaping Orthoptera to a very small segment such as is present in many larval forms. The volume of the femur is generally correlated with the size of the tibial muscles contained within it, but it is sometimes enlarged and modified in shape for other purposes than that of accommodating the tibial muscles. The tibia
Tibia
The tibia , shinbone, or shankbone is the larger and stronger of the two bones in the leg below the knee in vertebrates , and connects the knee with the ankle bones....
is characteristically a slender segment in adult insects, only a little shorter than the femur or the combined femur and trochanter. Its proximal end forms a more or less distinct head bent toward the femur, a device allowing the tibia to be flexed close against the under surface of the femur.
The tarsus
Tarsus
Tarsus may refer to:*Tarsus , a cluster of articulating bones in each foot** Tarsometatarsus, a fusion of the tarsus and metatarsus mainly found in birds...
of insects corresponds to the penultimate segment of a generalized arthropod limb, which is the segment called the propodite in Crustacea. adult insects it is commonly subdivided into from two to five subsegments, or tarsomeres, but in the Protura, some Collembola, and most holometabolous insect larvae it preserves the primitive form of a simple segment. The subsegments of the adult insect tarsus are usually freely movable on one another by inflected connecting membranes, but the tarsus never has intrinsic muscles. The tarsus of adult pterygote insects having fewer than five subsegments is probably specialized by the loss of one or more subsegments or by a fusion of adjoining subsegments. In the tarsi of Acrididae the long basal piece is evidently composed of three united tarsomeres, leaving the fourth and the fifth. The basal tarsomere is sometimes conspicuously enlarged and is distinguished as the basitarsus. On the under surfaces of the tarsal subsegments in certain Orthoptera there are small pads, the tarsal pulvilli, or euplantulae. The tarsus is occasionally fused with the tibia in larval insects, forming a tibiotarsal segment; in some cases it appears to be eliminated or reduced to a rudiment between the tibia and the pretarsus.
For the most part the femur and tibia are the longest leg segments but variations in the lengths and robustness of each segment relate to their functions. For example, gressorial and cursorial, or walking and running type insects respectively, usually have well-developed femora and tibiae on all legs, whereas jumping (saltatorial) insects such as grasshoppers have disproportionately developed hind femora and tibiae. In aquatic beetles (Coleoptera) and bugs (Hemiptera
Hemiptera
Hemiptera is an order of insects most often known as the true bugs , comprising around 50,000–80,000 species of cicadas, aphids, planthoppers, leafhoppers, shield bugs, and others...
), the tibia
Tibia
The tibia , shinbone, or shankbone is the larger and stronger of the two bones in the leg below the knee in vertebrates , and connects the knee with the ankle bones....
e and/or tarsi
Tarsi
The tarsi are two comparatively thick, elongated plates of dense connective tissue, about 2.5 cm. in length; one is found in each eyelid, and contributes to its form and support. They directly abut the lid margins.-Superior:...
of one or more pairs of legs usually are modified for swimming (natatorial) with fringes of long, slender hairs. Many ground-dwelling insects, such as mole crickets (Orthoptera: Gryllotalpidae), nymphal cicadas (Hemiptera: Cicadidae), and scarab beetles (Scarabaeidae
Scarabaeidae
The family Scarabaeidae as currently defined consists of over 30,000 species of beetles worldwide. The species in this large family are often called scarabs or scarab beetles. The classification of this family is fairly unstable, with numerous competing theories, and new proposals appearing quite...
), have the tibiae of the fore legs enlarged and modified for digging (fossorial), whereas the fore legs of some predatory insects, such as mantispid lacewings (Neuroptera
Neuroptera
The insect order Neuroptera, or net-winged insects, includes the lacewings, mantidflies, antlions, and their relatives. The order contains some 6,010 species...
) and mantids (Mantodea), are specialized for seizing prey, or raptorial. The tibia and basal tarsomere of each hind leg of honey bees are modified for the collection and carriage of pollen.
Abdomen
The ground plan of the abdomen of an adult insect typically consists of 11–12 segments and is less strongly sclerotized than the head or thorax. Each segment of the abdomen is represented by a sclerotized tergum, sternum, and perhaps a pleurite. Terga are separated from each other and from the adjacent sterna or pleura by a membrane. Spiracles are located in the pleural area. Variation of this ground plan includes the fusion of terga or terga and sterna to form continuous dorsal or ventral shields or a conical tube. Some insects bear a sclerite in the pleural area called a laterotergite. Ventral sclerites are sometimes called laterosternites. During the embryonic stage of many insects and the postembryonic stage of primitive insects, 11 abdominal segments are present. In modern insects there is a tendency toward reduction in the number of the abdominal segments, but the primitive number of 11 is maintained during embryogenesis.Variation in abdominal segment number is considerable. If the Apterygota are considered to be indicative of the ground plan for pterygotes, confusion reigns: adult Protura have 12 segments, Collembola have 6. The orthopteran family Acrididae has 11 segments, and a fossil specimen of Zoraptera has a 10-segmented abdomen.Generally, the first seven abdominal segments of adults (the pregenital segments) are similar in structure and lack appendages. However, apterygotes (bristletails and silverfish) and many immature aquatic insects have abdominal appendages. Apterygotes possess a pair of styles; rudimentary appendages that are serially homologous with the distal part of the thoracic legs. And, mesally, one or two pairs of protrusible (or exsertile) vesicles on at least some abdominal segments. These vesicles are derived from the coxal and trochanteral endites (inner annulated lobes) of the ancestral abdominal appendages. Aquatic larvae and nymphs may have gills laterally on some to most abdominal segments. Of the rest of the abdominal segments consist of the reproductive and anal parts.
The anal-genital part of the abdomen, known as the terminalia, consists generally of segments 8 or 9 to the abdominal apex. Segments 8 and 9 bear the genitalia; segment 10 is visible as a complete segment in many "lower” insects but always lacks appendages; and the small segment 11 is represented by a dorsal epiproct and pair of ventral paraprocts derived from the sternum. A pair of appendages, the cerci, articulates laterally on segment 11; typically these are annulated and filamentous but have been modified (e.g. the forceps of earwigs) or reduced in different insect orders. An annulated caudal filament, the median appendix dorsalis, arises from the tip of the epiproct in apterygotes, most mayflies (Ephemeroptera), and a few fossil insects. A similar structure in nymphal stoneflies (Plecoptera) is of uncertain homology. These terminal abdominal segments have excretory and sensory functions in all insects, but in adults there is an additional reproductive function.
External genitalia
The organs concerned specifically with mating and the deposition of eggs are known collectively as the external genitalia, although they may be largely internal. The components of the external genitalia of insects are very diverse in form and often have considerable taxonomic value, particularly amongst species that appear structurally similar in other respects. The male external genitalia have been used widely to aid in distinguishing species, whereas the female external genitalia may be simpler and less varied.The terminalia of adult female insects include internal structures for receiving the male copulatory organ and his spermatozoa and external structures used for oviposition (egg-laying; section 5.8). Most female insects have an egg-laying tube, or ovipositor; it is absent in termites, parasitic lice, many Plecoptera, and most Ephemeroptera. Ovipositors take two forms:
- true, or appendicular, formed from appendages of abdominal segments 8 and 9;
- substitutional, composed of extensible posterior abdominal segments.
Nervous system
The nervous systemNervous system
The nervous system is an organ system containing a network of specialized cells called neurons that coordinate the actions of an animal and transmit signals between different parts of its body. In most animals the nervous system consists of two parts, central and peripheral. The central nervous...
of an insect can be divided into a brain and a ventral nerve cord
Ventral nerve cord
The ventral nerve cord makes up the nervous system of some phyla of the invertebrates, particularly within the nematodes, annelids and the arthropods. It usually consists of cerebral ganglia anteriorly with the nerve cords running down the ventral plane of the organism...
. The head capsule is made up of six fused segments, each with a pair of ganglia
Ganglion
In anatomy, a ganglion is a biological tissue mass, most commonly a mass of nerve cell bodies. Cells found in a ganglion are called ganglion cells, though this term is also sometimes used to refer specifically to retinal ganglion cells....
, or a cluster of nerve cells outside of the brain. The first three pairs of ganglia are fused into the brain, while the three following pairs are fused into a structure of three pairs of ganglia under the insect's esophagus
Esophagus
The esophagus is an organ in vertebrates which consists of a muscular tube through which food passes from the pharynx to the stomach. During swallowing, food passes from the mouth through the pharynx into the esophagus and travels via peristalsis to the stomach...
, called the subesophageal ganglion
Subesophageal ganglion
The subesophageal ganglion of insects is composed of three pairs of fused ganglia. It controls the mouthparts, the salivary glands and certain muscles....
.
The thoracic segments have one ganglion on each side, which are connected into a pair, one pair per segment. This arrangement is also seen in the abdomen but only in the first eight segments. Many species of insects have reduced numbers of ganglia due to fusion or reduction. Some cockroaches have just six ganglia in the abdomen, whereas the wasp Vespa crabro has only two in the thorax and three in the abdomen. Some insects, like the house fly Musca domestica
Housefly
The housefly , Musca domestica, is a fly of the suborder Cyclorrhapha...
, have all the body ganglia fused into a single large thoracic ganglion.
At least a few insects have nociceptor
Nociceptor
A nociceptor is a sensory receptor that responds to potentially damaging stimuli by sending nerve signals to the spinal cord and brain. This process, called nociception, usually causes the perception of pain.-History:...
s, cells that detect and transmit sensations of pain
Pain in animals
Pain is a sensory and emotional experience often caused by intense or damaging stimuli. The International Association for the Study of Pain says pain is a conscious experience involving unpleasantness, i.e. suffering...
. This was discovered in 2003 by studying the variation in reactions of larvae
Larvae
In Roman mythology, lemures were shades or spirits of the restless or malignant dead, and are probably cognate with an extended sense of larvae as disturbing or frightening...
of the common fruitfly Drosophila
Drosophila
Drosophila is a genus of small flies, belonging to the family Drosophilidae, whose members are often called "fruit flies" or more appropriately pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many species to linger around overripe or rotting fruit...
to the touch of a heated probe and an unheated one. The larvae reacted to the touch of the heated probe with a stereotypical rolling behavior that was not exhibited when the larvae were touched by the unheated probe. Although nociception has been demonstrated in insects, there is not a consensus that insects feel pain consciously.
Digestive system
An insect uses its digestive system to extract nutrients and other substances from the food it consumes. Most of this food is ingested in the form of macromoleculeMacromolecule
A macromolecule is a very large molecule commonly created by some form of polymerization. In biochemistry, the term is applied to the four conventional biopolymers , as well as non-polymeric molecules with large molecular mass such as macrocycles...
s and other complex substances like protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
s, polysaccharide
Polysaccharide
Polysaccharides are long carbohydrate molecules, of repeated monomer units joined together by glycosidic bonds. They range in structure from linear to highly branched. Polysaccharides are often quite heterogeneous, containing slight modifications of the repeating unit. Depending on the structure,...
s, fat
Fat
Fats consist of a wide group of compounds that are generally soluble in organic solvents and generally insoluble in water. Chemically, fats are triglycerides, triesters of glycerol and any of several fatty acids. Fats may be either solid or liquid at room temperature, depending on their structure...
s, and nucleic acid
Nucleic acid
Nucleic acids are biological molecules essential for life, and include DNA and RNA . Together with proteins, nucleic acids make up the most important macromolecules; each is found in abundance in all living things, where they function in encoding, transmitting and expressing genetic information...
s. These macromolecules must be broken down by catabolic reaction
Catabolism
Catabolism is the set of metabolic pathways that break down molecules into smaller units and release energy. In catabolism, large molecules such as polysaccharides, lipids, nucleic acids and proteins are broken down into smaller units such as monosaccharides, fatty acids, nucleotides, and amino...
s into smaller molecules like amino acid
Amino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...
s and simple sugars before being used by cells of the body for energy, growth, or reproduction. This break-down process is known as digestion. The main structure of an insect's digestive system is a long enclosed tube called the alimentary canal, which runs lengthwise through the body. The alimentary canal directs food in one direction: from the mouth
Mouth
The mouth is the first portion of the alimentary canal that receives food andsaliva. The oral mucosa is the mucous membrane epithelium lining the inside of the mouth....
to the anus
Anus
The anus is an opening at the opposite end of an animal's digestive tract from the mouth. Its function is to control the expulsion of feces, unwanted semi-solid matter produced during digestion, which, depending on the type of animal, may be one or more of: matter which the animal cannot digest,...
. It has three sections, each of which performs a different process of digestion. In addition to the alimentary canal, insects also have paired salivary glands and salivary reservoirs. These structures usually reside in the thorax, adjacent to the foregut. The gut is where almost all of insects' digestion takes place. It can be divided into the foregut
Foregut
The foregut is the anterior part of the alimentary canal, from the mouth to the duodenum at the entrance of the bile duct. At this point it is continuous with the midgut...
, midgut
Stomach
The stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects , and molluscs. It is involved in the second phase of digestion, following mastication .The stomach is...
and hindgut
Hindgut
The hindgut is the posterior part of the alimentary canal. In mammals, it includes the distal third of the transverse colon and the splenic flexure, the descending colon, sigmoid colon and rectum.-Blood flow:...
.
Foregut
The first section of the alimentary canal is the foregutForegut
The foregut is the anterior part of the alimentary canal, from the mouth to the duodenum at the entrance of the bile duct. At this point it is continuous with the midgut...
(element 27 in numbered diagram), or stomodaeum. The foregut is line with a cuticular lining made of chitin
Chitin
Chitin n is a long-chain polymer of a N-acetylglucosamine, a derivative of glucose, and is found in many places throughout the natural world...
and protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
s as protection from tough food. The foregut includes the buccal cavity (mouth), pharynx
Pharynx
The human pharynx is the part of the throat situated immediately posterior to the mouth and nasal cavity, and anterior to the esophagus and larynx. The human pharynx is conventionally divided into three sections: the nasopharynx , the oropharynx , and the laryngopharynx...
, esophagus
Esophagus
The esophagus is an organ in vertebrates which consists of a muscular tube through which food passes from the pharynx to the stomach. During swallowing, food passes from the mouth through the pharynx into the esophagus and travels via peristalsis to the stomach...
, and Crop
Crop (anatomy)
A crop is a thin-walled expanded portion of the alimentary tract used for the storage of food prior to digestion that is found in many animals, including gastropods, earthworms, leeches, insects, birds, and even some dinosaurs.- Bees :Cropping is used by bees to temporarily store nectar of flowers...
and proventriculus
Proventriculus
The proventriculus is part of the digestive system of birds, invertebrates and insects.-Birds:The proventriculus is a standard part of avian anatomy...
(any part may be highly modified) which both store food and signify when to continue passing onward to the midgut. Here, digestion starts as partially chewed food is broken down by saliva from the salivary glands. As the salivary glands produce fluid and carbohydrate-digesting enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
s (mostly amylase
Amylase
Amylase is an enzyme that catalyses the breakdown of starch into sugars. Amylase is present in human saliva, where it begins the chemical process of digestion. Food that contains much starch but little sugar, such as rice and potato, taste slightly sweet as they are chewed because amylase turns...
s), strong muscles in the pharynx pump fluid into the buccal cavity, lubricating the food like the salivarium does, and helping blood feeders, and xylem and phloem feeders.
From there, the pharynx passes food to the esophagus, which could be just a simple tube passing it on to the crop and proventriculus, and then on ward to the midgut, as in most insects. Alternately, the foregut may expand into a very enlarged crop and proventriculus, or the crop could just be a diverticulum
Diverticulum
A diverticulum is medical or biological term for an outpouching of a hollow structure in the body. Depending upon which layers of the structure are involved, they are described as being either true or false....
, or fluid filled structure, as in some Diptera species.
Midgut
Once food leaves the crop, it passes to the midgutStomach
The stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects , and molluscs. It is involved in the second phase of digestion, following mastication .The stomach is...
(element 13 in numbered diagram), also known as the mesenteron, where the majority of digestion takes place. Microscopic projections from the midgut wall, called microvilli
Microvillus
Microvilli are microscopic cellular membrane protrusions that increase the surface area of cells, and are involved in a wide variety of functions, including absorption, secretion, cellular adhesion, and mechanotransduction....
, increase the surface area of the wall and allow more nutrients to be absorbed; they tend to be close to the origin of the midgut. In some insects, the role of the microvilli and where they are located may vary. For example, specialized microvilli producing digestive enzymes may more likely be near the end of the midgut, and absorption near the origin or beginning of the midgut.
Hindgut
In the hindgutHindgut
The hindgut is the posterior part of the alimentary canal. In mammals, it includes the distal third of the transverse colon and the splenic flexure, the descending colon, sigmoid colon and rectum.-Blood flow:...
(element 16 in numbered diagram), or proctodaeum, undigested food particles are joined by uric acid
Uric acid
Uric acid is a heterocyclic compound of carbon, nitrogen, oxygen, and hydrogen with the formula C5H4N4O3. It forms ions and salts known as urates and acid urates such as ammonium acid urate. Uric acid is created when the body breaks down purine nucleotides. High blood concentrations of uric acid...
to form fecal pellets. The rectum absorbs 90% of the water in these fecal pellets, and the dry pellet is then eliminated through the anus (element 17), completing the process of digestion. The uric acid is formed using hemolymph waste products diffused from the Malpighian tubule
Malpighian tubule system
The Malpighian tubule system is a type of excretory and osmoregulatory system found in some Uniramia , arachnids and tardigrades....
s (element 20). It is then emptied directly into the alimentary canal, at the junction between the midgut and hindgut. The number of Malpighian tubules possessed by a given insect varies between species, ranging from only two tubules in some insects to over 100 tubules in others.
Respiratory systems
Insect respiration is accomplished without lungLung
The lung is the essential respiration organ in many air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located near the backbone on either side of the heart...
s. Instead, the insect respiratory system uses a system of internal tubes and sacs through which gases either diffuse or are actively pumped, delivering oxygen directly to tissues that need it via their trachea
Invertebrate trachea
The invertebrate trachea refers to the open respiratory system composed of spiracles, tracheae, and tracheoles that terrestrial arthropods have to transport metabolic gases to and from tissues....
(element 8 in numbered diagram). Since oxygen is delivered directly, the circulatory system is not used to carry oxygen, and is therefore greatly reduced. The insect circulatory system has no vein
Vein
In the circulatory system, veins are blood vessels that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated blood to the heart...
s or arterie
Artery
Arteries are blood vessels that carry blood away from the heart. This blood is normally oxygenated, exceptions made for the pulmonary and umbilical arteries....
s, and instead consists of little more than a single, perforated dorsal tube which pulses peristaltically
Peristalsis
Peristalsis is a radially symmetrical contraction and relaxation of muscles which propagates in a wave down the muscular tube, in an anterograde fashion. In humans, peristalsis is found in the contraction of smooth muscles to propel contents through the digestive tract. Earthworms use a similar...
. Toward the thorax, the dorsal tube (element 14) divides into chambers and acts like the insect's heart. The opposite end of the dorsal tube is like the aorta of the insect circulating the hemolymph
Hemolymph
Hemolymph, or haemolymph, is a fluid in the circulatory system of some arthropods and is analogous to the fluids and cells making up both blood and interstitial fluid in vertebrates such as birds and mammals...
, arthropods' fluid analog of blood
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....
, inside the body cavity. Air is taken in through openings on the sides of the abdomen called spiracle
Spiracle
Spiracles are openings on the surface of some animals that usually lead to respiratory systems.-Vertebrates:The spiracle is a small hole behind each eye that opens to the mouth in some fishes. In the primitive jawless fish the first gill opening immediately behind the mouth is essentially similar...
s.
There are many different patterns of gas exchange
Gas exchange
Gas exchange is a process in biology where gases contained in an organism and atmosphere transfer or exchange. In human gas-exchange, gases contained in the blood of human bodies exchange with gases contained in the atmosphere. Human gas-exchange occurs in the lungs...
demonstrated by different groups of insects. Gas exchange patterns in insects can range from continuous and diffusive
Diffusion
Molecular diffusion, often called simply diffusion, is the thermal motion of all particles at temperatures above absolute zero. The rate of this movement is a function of temperature, viscosity of the fluid and the size of the particles...
ventilation, to discontinuous gas exchange
Discontinuous gas exchange
Discontinuous gas-exchange cycles , also called discontinuous ventilation or discontinuous ventilatory cycles, follow one of several patterns of arthropod gas exchange that have been documented primarily in insects; they occur when the insect is at rest...
. During continuous gas exchange, oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
is taken in and carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
is released in a continuous cycle. In discontinuous gas exchange, however, the insect takes in oxygen while it is active and small amounts of carbon dioxide are released when the insect is at rest. Diffusive ventilation is simply a form of continuous gas exchange that occurs by diffusion
Diffusion
Molecular diffusion, often called simply diffusion, is the thermal motion of all particles at temperatures above absolute zero. The rate of this movement is a function of temperature, viscosity of the fluid and the size of the particles...
rather than physically taking in the oxygen. Some species of insect that are submerged also have adaptations to aid in respiration. As larvae, many insects have gills that can extract oxygen dissolved in water, while others need to rise to the water surface to replenish air supplies which may be held or trapped in special structures.
Circulatory system
Insect blood or haemolymph’s main function is that of transport and it bathes the insect’s body organs. Making up usually less than 25% of an insect’s body weight, it transports hormones, nutrients and wastes and has a role in, osmoregulation, temperature control, immunityImmunity (medical)
Immunity is a biological term that describes a state of having sufficient biological defenses to avoid infection, disease, or other unwanted biological invasion. Immunity involves both specific and non-specific components. The non-specific components act either as barriers or as eliminators of wide...
, storage (water, carbohydrates and fats) and skeletal function. It also plays an essential part in the moulting process. An additional role of the haemolymph in some orders, can be that of predatory defence. It can contain unpalatable and malodourous chemicals that will act as a deterrent to predators. Haemolymph contains molecules, ions and cells; regulating chemical exchanges between tissues
Tissue (biology)
Tissue is a cellular organizational level intermediate between cells and a complete organism. A tissue is an ensemble of cells, not necessarily identical, but from the same origin, that together carry out a specific function. These are called tissues because of their identical functioning...
, haemolymph is encased in the insect body cavity or haemocoel. It is transported around the body by combined heart (posterior) and aorta
Aorta
The aorta is the largest artery in the body, originating from the left ventricle of the heart and extending down to the abdomen, where it branches off into two smaller arteries...
(anterior) pulsations which are located dorsally just under the surface of the body. It differs from vertebrate
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
blood in that it doesn’t contain any red blood cells and therefore is without high oxygen carrying capacity, and is more similar to lymph
Lymph
Lymph is considered a part of the interstitial fluid, the fluid which lies in the interstices of all body tissues. Interstitial fluid becomes lymph when it enters a lymph capillary...
found in vertebrates.
Body fluids enter through one way valved ostia which are openings situated along the length of the combined aorta and heart organ. Pumping of the haemolymph occurs by waves of peristaltic contraction, originating at the body's posterior end, pumping forwards into the dorsal vessel, out via the aorta and then into the head where it flows out into the haemocoel. The haemolymph is circulated to the appendages unidirectionally with the aid of muscular pumps or accessory pulsatile organs which are usually found at the base of the antennae
Antenna (biology)
Antennae in biology have historically been paired appendages used for sensing in arthropods. More recently, the term has also been applied to cilium structures present in most cell types of eukaryotes....
or wings and sometimes in the legs, with pumping rates accelerating with periods of increased activity. Movement of haemolymph is particularly important for thermoregulation in orders such as Odonata
Odonata
Odonata is an order of insects, encompassing dragonflies and damselflies . The word dragonfly is also sometimes used to refer to all Odonata, but the back-formation odonate is a more correct English name for the group as a whole...
, Lepidoptera
Lepidoptera
Lepidoptera is a large order of insects that includes moths and butterflies . It is one of the most widespread and widely recognizable insect orders in the world, encompassing moths and the three superfamilies of butterflies, skipper butterflies, and moth-butterflies...
, Hymenoptera
Hymenoptera
Hymenoptera is one of the largest orders of insects, comprising the sawflies, wasps, bees and ants. There are over 130,000 recognized species, with many more remaining to be described. The name refers to the heavy wings of the insects, and is derived from the Ancient Greek ὑμήν : membrane and...
and Diptera
Diptera
Diptera , or true flies, is the order of insects possessing only a single pair of wings on the mesothorax; the metathorax bears a pair of drumstick like structures called the halteres, the remnants of the hind wings. It is a large order, containing an estimated 240,000 species, although under half...
.
Endocrine system
The salivary glandSalivary gland
The salivary glands in mammals are exocrine glands, glands with ducts, that produce saliva. They also secrete amylase, an enzyme that breaks down starch into maltose...
s (element 30 in numbered diagram) in an insect's mouth produce saliva. The salivary ducts lead from the glands to the reservoirs and then forward through the head to an opening called the salivarium, located behind the hypopharynx. By moving its mouthparts (element 32 in numbered diagram) the insect can mix its food with saliva. The mixture of saliva and food then travels through the salivary tubes into the mouth, where it begins to break down. Some insects, like flies
Diptera
Diptera , or true flies, is the order of insects possessing only a single pair of wings on the mesothorax; the metathorax bears a pair of drumstick like structures called the halteres, the remnants of the hind wings. It is a large order, containing an estimated 240,000 species, although under half...
, have extra-oral digestion
Mastication
Mastication or chewing is the process by which food is crushed and ground by teeth. It is the first step of digestion and it increases the surface area of foods to allow more efficient break down by enzymes. During the mastication process, the food is positioned between the teeth for grinding by...
. Insects using extra-oral digestion expel digestive enzymes onto their food to break it down. This strategy allows insects to extract a significant proportion of the available nutrients from the food source.
Female
Female insects are able make eggs, receive and store sperm, manipulate sperm from different males, and lay eggs. Their reproductive systems are made up of a pair of ovaries, accessory glands, one or more spermathecaSpermatheca
The spermatheca , also called receptaculum seminis , is an organ of the female reproductive tract in insects, some molluscs, oligochaeta worms and certain other invertebrates and vertebrates...
e, and ducts connecting these parts. The ovaries make eggs and accessory glands produce the substances to help package and lay the eggs. Spermathecae store sperm for varying periods of time and, along with portions of the oviduct
Oviduct
In non-mammalian vertebrates, the passageway from the ovaries to the outside of the body is known as the oviduct. The eggs travel along the oviduct. These eggs will either be fertilized by sperm to become a zygote, or will degenerate in the body...
s, can control sperm use. The ducts and spermathecae are lined with a cuticle.
The ovaries are made up of a number of egg tubes, called ovarioles
Ovarioles
An ovariole is one of the tubes of which the ovaries of most insects are composed. Typically an insect will have two ovaries. The constituent ovarioles lead to two oviducts, which converge into a single oviduct. The ovarioles are composed of a germarium and a set of ovarial follicles.-In D...
, which vary in size and number by species. The number of eggs that the insect is able to make vary by the number of ovarioles with the rate that eggs can be develop being also influenced by ovariole design. In meroistic ovaries, the eggs-to-be divide repeatedly and most of the daughter cells become helper cells for a single oocyte
Oocyte
An oocyte, ovocyte, or rarely ocyte, is a female gametocyte or germ cell involved in reproduction. In other words, it is an immature ovum, or egg cell. An oocyte is produced in the ovary during female gametogenesis. The female germ cells produce a primordial germ cell which undergoes a mitotic...
in the cluster. In panoistic ovaries, each egg-to-be produced by stem germ cells develops into an oocyte; there are no helper cells from the germ line. Production of eggs by panoistic ovaries tends to be slower than that by meroistic ovaries.
Accessory glands or glandular parts of the oviducts produce a variety of substances for sperm maintenance, transport, and fertilization, as well as for protection of eggs. They can produce glue and protective substances for coating eggs or tough coverings for a batch of eggs called ootheca
Ootheca
An ootheca is a type of egg mass made by any member of a variety of species .The word is a latinized combination of oo-, meaning "egg", from the Greek word ōon , and theca, meaning a "cover" or "container", from the Greek theke...
e. Spermathecae are tubes or sacs in which sperm can be stored between the time of mating and the time an egg is fertilized. Paternity testing of insects has revealed that some, and probably many, female insects use the spermatheca and various ducts to control or bias sperm used in favor of some males over others.
Male
The main component of the male reproductive system is the testis, suspended in the body cavity by tracheaTrachea
Trachea may refer to:* Vertebrate trachea, or windpipe, in terrestrial vertebrates, such as birds and mammals* Invertebrate trachea, in terrestrial invertebrates, such as insects and crustaceans* Vessel elements in plants...
e and the fat body. The more primitive apterygote
Apterygota
The name Apterygota is sometimes applied to a subclass of small, agile insects, distinguished from other insects by their lack of wings in the present and in their evolutionary history...
insects have a single testis, and in some lepidopterans
Lepidoptera
Lepidoptera is a large order of insects that includes moths and butterflies . It is one of the most widespread and widely recognizable insect orders in the world, encompassing moths and the three superfamilies of butterflies, skipper butterflies, and moth-butterflies...
the two maturing testes are secondarily fused into one structure during the later stages of larval development, although the ducts leading from them remain separate. However, most male insects have a pair of testes, inside of which are sperm tubes or follicles that are enclosed within a membranous sac. The follicles connect to the vas deferens by the vas efferens, and the two tubular vasa deferentia connect to a median ejaculatory duct that leads to the outside. A portion of the vas deferens is often enlarged to form the seminal vesicle, which stores the sperm before they are discharged into the female. The seminal vesicles have glandular linings that secrete nutrients for nourishment and maintenance of the sperm. The ejaculatory duct is derived from an invagination of the epidermal cells during development and, as a result, has a cuticular lining. The terminal portion of the ejaculatory duct may be sclerotized to form the intromittent organ, the aedeagus. The remainder of the male reproductive system is derived from embryonic mesoderm, except for the germ cells, or spermatogonia, which descend from the primordial pole cells very early during embryogenesis.
Blattodea
Cockroaches are most common in tropical and subtropical climates. Some species are in close association with human dwellings and widely found around garbage or in the kitchen. Cockroaches are generally omnivorous with the exception of the woodWood
Wood is a hard, fibrous tissue found in many trees. It has been used for hundreds of thousands of years for both fuel and as a construction material. It is an organic material, a natural composite of cellulose fibers embedded in a matrix of lignin which resists compression...
-eating species such as Cryptocercus
Cryptocercus
Cryptocercus is a genus of Dictyoptera in the family Polyphagidae, of which this genus is the only member. Species are known as wood roaches or brown-hooded cockroaches....
; these roaches are incapable of digesting cellulose
Cellulose
Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to over ten thousand β linked D-glucose units....
themselves, but have symbiotic relationships with various protozoa
Protozoa
Protozoa are a diverse group of single-cells eukaryotic organisms, many of which are motile. Throughout history, protozoa have been defined as single-cell protists with animal-like behavior, e.g., movement...
ns and bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
that digest the cellulose, allowing them to extract the nutrients. The similarity of these symbionts in the genus Cryptocercus to those in termite
Termite
Termites are a group of eusocial insects that, until recently, were classified at the taxonomic rank of order Isoptera , but are now accepted as the epifamily Termitoidae, of the cockroach order Blattodea...
s are such that it has been suggested that they are more closely related to termite
Termite
Termites are a group of eusocial insects that, until recently, were classified at the taxonomic rank of order Isoptera , but are now accepted as the epifamily Termitoidae, of the cockroach order Blattodea...
s than to other cockroaches, and current research strongly supports this hypothesis of relationships. All species studied so far carry the obligate mutualistic endosymbiont bacterium Blattabacterium
Blattabacterium
Blattabacterium in an obligate mutualistic endosymbiont bacterium that is believed to inhabit all species of cockroach studied to date, with the exception of Nocticola species. B...
, with the exception of Nocticola australiensis, an Australian cave dwelling species without eyes, pigment or wings, and which recent genetic studies indicates are very primitive cockroaches.
Cockroaches, like all insects, breathe through a system of tubes called tracheae
Invertebrate trachea
The invertebrate trachea refers to the open respiratory system composed of spiracles, tracheae, and tracheoles that terrestrial arthropods have to transport metabolic gases to and from tissues....
. The tracheae of insects are attached to the spiracle
Spiracle
Spiracles are openings on the surface of some animals that usually lead to respiratory systems.-Vertebrates:The spiracle is a small hole behind each eye that opens to the mouth in some fishes. In the primitive jawless fish the first gill opening immediately behind the mouth is essentially similar...
s, excluding the head. Thus cockroaches, like all insects, are not dependent on the mouth and windpipe to breathe. The valves open when the CO2
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
level in the insect rises to a high level; then the CO2 diffuses
Diffusion
Molecular diffusion, often called simply diffusion, is the thermal motion of all particles at temperatures above absolute zero. The rate of this movement is a function of temperature, viscosity of the fluid and the size of the particles...
out of the tracheae to the outside and fresh O2 diffuses in. Unlike in vertebrates that depend on blood
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....
for transporting O2 and CO2, the tracheal system brings the air directly to cells
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
, the tracheal tubes branching continually like a tree until their finest divisions, tracheoles, are associated with each cell, allowing gaseous oxygen to dissolve in the cytoplasm lying across the fine cuticle lining of the tracheole. CO2 diffuses out of the cell into the tracheole. While cockroaches do not have lungs and thus do not actively breathe in the vertebrate lung manner, in some very large species the body musculature may contract rhythmically to forcibly move air out and in the spiracles; this may be considered a form of breathing.
Coleoptera
The digestive system of beetles is primarily based on plants which they for the most part feed upon, with mostly the anterior midgutMidgut
The midgut is the portion of the embryo from which most of the intestines develop. After it bends around the superior mesenteric artery, it is called the "midgut loop"...
performing digestion. Although, in predatory species (e.g., Carabidae) most digestion occurs in the crop by means of midgut enzymes. In Elateridae species, the predatory larvae defecate enzymes on their prey, with digestion being extraorally. The alimentary canal basically comprises a short narrow pharynx
Pharynx
The human pharynx is the part of the throat situated immediately posterior to the mouth and nasal cavity, and anterior to the esophagus and larynx. The human pharynx is conventionally divided into three sections: the nasopharynx , the oropharynx , and the laryngopharynx...
, a widened expansion, the crop
Crop
Crop may refer to:* Crop, a plant grown and harvested for agricultural use* Crop , part of the alimentary tract of some animals* Crop , a modified whip used in horseback riding or disciplining humans...
and a poorly developed gizzard
Gizzard
The gizzard, also referred to as the ventriculus, gastric mill, and gigerium, is an organ found in the digestive tract of some animals, including birds, reptiles, earthworms and some fish. This specialized stomach constructed of thick, muscular walls is used for grinding up food; often rocks are...
. After there is a midgut, that varies in dimensions between species, with a large amount of cecum
Cecum
The cecum or caecum is a pouch, connecting the ileum with the ascending colon of the large intestine. It is separated from the ileum by the ileocecal valve or Bauhin's valve, and is considered to be the beginning of the large intestine. It is also separated from the colon by the cecocolic...
, with a hingut, with varying lengths. There are typically four to six Malpighian tubules.
The nervous system
Nervous system
The nervous system is an organ system containing a network of specialized cells called neurons that coordinate the actions of an animal and transmit signals between different parts of its body. In most animals the nervous system consists of two parts, central and peripheral. The central nervous...
in beetles contains all the types found in insects, varying between different species. With three thoracic and seven or eight abdominal ganglia can be distinguished to that in which all the thoracic and abdominal ganglia are fused to form a composite structure. Oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
is obtained via a tracheal system
Invertebrate trachea
The invertebrate trachea refers to the open respiratory system composed of spiracles, tracheae, and tracheoles that terrestrial arthropods have to transport metabolic gases to and from tissues....
. Air enters a series of tubes along the body through openings called spiracle
Spiracle
Spiracles are openings on the surface of some animals that usually lead to respiratory systems.-Vertebrates:The spiracle is a small hole behind each eye that opens to the mouth in some fishes. In the primitive jawless fish the first gill opening immediately behind the mouth is essentially similar...
s, and is then taken into increasingly finer fibers. Pumping movements of the body force the air through the system. Beetles have hemolymph
Hemolymph
Hemolymph, or haemolymph, is a fluid in the circulatory system of some arthropods and is analogous to the fluids and cells making up both blood and interstitial fluid in vertebrates such as birds and mammals...
instead of blood
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....
like other insect species, the open circulatory system of the beetle is driven by a tube-like heart attached to the top inside of the thorax. Some species of diving beetle
Dytiscidae
Dytiscidae – based on the Greek dytikos , "able to dive" – are the predaceous diving beetles, a family of water beetles. They are about 25 mm long on average, though there is much variation between species. Dytiscus latissimus, the largest, can grow up to 45 mm long...
s (Dytiscidae) carry a bubble of air with them whenever they dive beneath the water surface. This bubble may be held under the elytra or it may be trapped against the body using specialized hairs. The bubble usually covers one or more spiracles so the insect can breathe air from the bubble while submerged. An air bubble provides an insect with only a short-term supply of oxygen, but thanks to its unique physical properties, oxygen will diffuse into the bubble and displacing the nitrogen, called passive diffusion, however the volume of the bubble eventually diminishes and the beetle will have to return to the surface.
Different glands specialize for different pheromones produced for finding mates. Pheromones from species of Rutelinea are produced from epithelial cell
Epithelium
Epithelium is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. Epithelial tissues line the cavities and surfaces of structures throughout the body, and also form many glands. Functions of epithelial cells include secretion, selective...
s lining the inner surface of the apical abdominal segments or amino acid based pheromones of Melolonthinae
Melolonthinae
Melolonthinae is a subfamily of the scarab beetles . It is a very diverse group; distributed over most of the world, it contains many familiar species. Some authors include the scarab subfamilies Euchirinae and Pachypodinae as tribes in the Melolonthinae.Unlike some of their relatives, their...
from eversible glands on the abdominal apex. Other species produce different types of pheromones. Dermestids produce ester
Ester
Esters are chemical compounds derived by reacting an oxoacid with a hydroxyl compound such as an alcohol or phenol. Esters are usually derived from an inorganic acid or organic acid in which at least one -OH group is replaced by an -O-alkyl group, and most commonly from carboxylic acids and...
s, and species of Elateridae produce fatty-acid-derived aldehyde
Aldehyde
An aldehyde is an organic compound containing a formyl group. This functional group, with the structure R-CHO, consists of a carbonyl center bonded to hydrogen and an R group....
s and acetate
Acetate
An acetate is a derivative of acetic acid. This term includes salts and esters, as well as the anion found in solution. Most of the approximately 5 billion kilograms of acetic acid produced annually in industry are used in the production of acetates, which usually take the form of polymers. In...
s. For means of finding a mate also, fireflies (Lampyridae) utilized modified fat body cells woth transparent surfaces backed with reflective uric acid crystals to biosynthetically produce light, or bioluminescence
Bioluminescence
Bioluminescence is the production and emission of light by a living organism. Its name is a hybrid word, originating from the Greek bios for "living" and the Latin lumen "light". Bioluminescence is a naturally occurring form of chemiluminescence where energy is released by a chemical reaction in...
. The light produce is highly efficient, as it is produced by oxidation of luciferin
Firefly luciferin
Firefly luciferin is the luciferin, or light-emitting compound, found in many firefly species. It is the substrate of luciferase , which is responsible for the characteristic yellow light emission from many firefly species...
by the enzymes luciferase
Luciferase
Luciferase is a generic term for the class of oxidative enzymes used in bioluminescence and is distinct from a photoprotein. One famous example is the firefly luciferase from the firefly Photinus pyralis. "Firefly luciferase" as a laboratory reagent usually refers to P...
in the presence of ATP
Adenosine triphosphate
Adenosine-5'-triphosphate is a multifunctional nucleoside triphosphate used in cells as a coenzyme. It is often called the "molecular unit of currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism...
(adenosine triphospate) and oxygen, producing oxyluciferin, carbon dioxide, and light.
A notable number of species have developed special glands that produce chemicals for deterring predators (see Defense and predation). The Ground beetle
Ground beetle
Ground beetles are a large, cosmopolitan family of beetles, Carabidae, with more than 40,000 species worldwide, approximately 2,000 of which are found in North America and 2,700 in Europe.-Description and ecology:...
's (of Carabidae) defensive glands, located at the posterior, produce a variety of hydrocarbon
Hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....
s, aldehyde
Aldehyde
An aldehyde is an organic compound containing a formyl group. This functional group, with the structure R-CHO, consists of a carbonyl center bonded to hydrogen and an R group....
s, phenol
Phenol
Phenol, also known as carbolic acid, phenic acid, is an organic compound with the chemical formula C6H5OH. It is a white crystalline solid. The molecule consists of a phenyl , bonded to a hydroxyl group. It is produced on a large scale as a precursor to many materials and useful compounds...
s, quinone
Quinone
A quinone is a class of organic compounds that are formally "derived from aromatic compounds [such as benzene or naphthalene] by conversion of an even number of –CH= groups into –C– groups with any necessary rearrangement of double bonds," resulting in "a fully conjugated cyclic dione structure."...
s, ester
Ester
Esters are chemical compounds derived by reacting an oxoacid with a hydroxyl compound such as an alcohol or phenol. Esters are usually derived from an inorganic acid or organic acid in which at least one -OH group is replaced by an -O-alkyl group, and most commonly from carboxylic acids and...
s, and acid
Acid
An acid is a substance which reacts with a base. Commonly, acids can be identified as tasting sour, reacting with metals such as calcium, and bases like sodium carbonate. Aqueous acids have a pH of less than 7, where an acid of lower pH is typically stronger, and turn blue litmus paper red...
s released from an opening at the end of the abdomen. While African carabid beetles (e.g., Anthia some of which used to comprise the genus Thermophilum) employ the same chemicals as ants: formic acid
Formic acid
Formic acid is the simplest carboxylic acid. Its chemical formula is HCOOH or HCO2H. It is an important intermediate in chemical synthesis and occurs naturally, most notably in the venom of bee and ant stings. In fact, its name comes from the Latin word for ant, formica, referring to its early...
. While Bombardier beetle
Bombardier beetle
Bombardier beetles are ground beetles in the tribes Brachinini, Paussini, Ozaenini, or Metriini—more than 500 species altogether—which are most notable for the defense mechanism that gives them their name: When disturbed, the beetle ejects a noxious chemical spray in a rapid burst of pulses from...
s have well developed, like other carabid beetles, pygidial glands that empty from the lateral edges of the intersegment membranes between the seventh and eighth abdominal segments. The gland is made of two containing chambers. The first holds hydroquinone
Hydroquinone
Hydroquinone, also benzene-1,4-diol or quinol, is an aromatic organic compound that is a type of phenol, having the chemical formula C6H42. Its chemical structure, shown in the table at right, has two hydroxyl groups bonded to a benzene ring in a para position. It is a white granular solid...
s and hydrogen peroxide
Hydrogen peroxide
Hydrogen peroxide is the simplest peroxide and an oxidizer. Hydrogen peroxide is a clear liquid, slightly more viscous than water. In dilute solution, it appears colorless. With its oxidizing properties, hydrogen peroxide is often used as a bleach or cleaning agent...
, with the second holding just hydrogen peroxide plus catalase
Catalase
Catalase is a common enzyme found in nearly all living organisms that are exposed to oxygen, where it catalyzes the decomposition of hydrogen peroxide to water and oxygen...
s. These chemicals mix and result in an explosive ejection, forming temperatures of around 100 C, with the brake down of hydroquinone to H2 + O2 + quinone, with the O2 propelling the excretion.
Tympanal organ
Tympanal organ
A tympanal organ is a hearing organ in insects, consisting of a membrane stretched across a frame backed by an air sac and associated sensory neurons...
s or hearing organs, which is a membrane (tympanum) stretched across a frame backed by an air sac and associated sensory neurons, are described in two families. Several species of the genus Cicindela
Cicindela
Cicindela are generally brightly colored and metallic beetles, often with some sort of patterning of ivory or cream-colored markings. They are most abundant and diverse in habitats with sandy soil , and very often near bodies of water, even if seasonally transient; along river, sea and lake shores,...
(Cicindelidae) have ears on the dorsal surface of the first abdominal segment beneath the wing; two tribes tribes in the family Dynastinae (Scarabaeidae
Scarabaeidae
The family Scarabaeidae as currently defined consists of over 30,000 species of beetles worldwide. The species in this large family are often called scarabs or scarab beetles. The classification of this family is fairly unstable, with numerous competing theories, and new proposals appearing quite...
) have ears just beneath the pronotal shield or neck membrane. The ears of both families are to ultrasonic frequencies, with strong evidence that they function to detect the presence of bats via there ultrasonic echolocation. Even though beetles constitute a large order and live in a variety of niche
Niche
Niche may refer to:*Niche , an exedra or an apse that has been reduced in size;*Niche , Colombian/Spanish football player, full name Víctor Manuel Micolta Armero*Niche , a British Thoroughbred racehorse...
s, examples of hearing is surprisingly lacking in species, though it is likely that most are just undiscovered.
Dermaptera
The neuroendocrine systemNeuroendocrinology
Neuroendocrinology is the study of the extensive interactions between the nervous system and the endocrine system, including the biological features of the cells that participate, and how they functionally communicate...
consist of what typical insect would. There is a Brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
, a subesophageal ganglion, three thoratic ganglia, and six abdominal ganglia; a ganglion being a mass of neuron
Neuron
A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...
s.
Strong neuron connects connect the neurohemal corpora cardiaca to the brain and frontal ganglion, where the closely related median corpus allatum
Corpus allatum
The corpus allatum , in insect physiology, is an endocrine gland which generates juvenile hormone; as such, it plays a crucial role in metamorphosis. Surgical removal of the corpora allata can cause an immature larva to pupate at its next molt, resulting in a miniature adult...
produces Jeuvenile hormone III in close proximity to the neurohemal dorsal arota. The digestive system of earwigs is like all other insects: consisting of a fore-, mid-, and hindgut, albeit, earwigs lack gastric caecae which specialize in many species of insects for digestion. Long, slender (extratory) malpighian tubules can be found between the junction of the mid- and hind gut.
The reproductive system of females consist of paired ovarie
Ovary
The ovary is an ovum-producing reproductive organ, often found in pairs as part of the vertebrate female reproductive system. Ovaries in anatomically female individuals are analogous to testes in anatomically male individuals, in that they are both gonads and endocrine glands.-Human anatomy:Ovaries...
s, lateral oviduct
Oviduct
In non-mammalian vertebrates, the passageway from the ovaries to the outside of the body is known as the oviduct. The eggs travel along the oviduct. These eggs will either be fertilized by sperm to become a zygote, or will degenerate in the body...
s, spermatheca
Spermatheca
The spermatheca , also called receptaculum seminis , is an organ of the female reproductive tract in insects, some molluscs, oligochaeta worms and certain other invertebrates and vertebrates...
, and a genital chamber
Sex organ
A sex organ, or primary sexual characteristic, as narrowly defined, is any of the anatomical parts of the body which are involved in sexual reproduction and constitute the reproductive system in a complex organism; flowers are the reproductive organs of flowering plants, cones are the reproductive...
. The lateral ducts are where the eggs leave the body, while the spermatheca is where sperm is stored. Unlike other insects, the gonopore
Gonopore
A gonopore, sometimes called a gonadopore, is a genital pore in many invertebrates. Hexapods, including insects have a single common gonopore, except mayflies, which have a pair of gonopores...
, or genital opening is behind the seventh abdominal segment. The ovaries are primitive in that they are polytrophic; or the nurse cell
Nurse cell
-Human physiology:Nurse cells are specialized macrophages residing in the bone marrow that assist in the development of red blood cells. They absorb the nuclei of immature red blood cells and may provide growth factors to help the red blood cells mature...
s and oocyte
Oocyte
An oocyte, ovocyte, or rarely ocyte, is a female gametocyte or germ cell involved in reproduction. In other words, it is an immature ovum, or egg cell. An oocyte is produced in the ovary during female gametogenesis. The female germ cells produce a primordial germ cell which undergoes a mitotic...
s alternate along the length of the ovariole. In some species these long ovarioles branch off the lateral duct, while in others, short ovarioles appear around the duct.
Diptera
The genitalia of female flies are rotated to a varying degree from the position found in other insects. In some flies this is a temporary rotation during mating, but in others it is a permanent torsion of the organs that occurs during the pupal stage. This torsion may lead to the anusAnus
The anus is an opening at the opposite end of an animal's digestive tract from the mouth. Its function is to control the expulsion of feces, unwanted semi-solid matter produced during digestion, which, depending on the type of animal, may be one or more of: matter which the animal cannot digest,...
being located below the genitals, or, in the case of 360° torsion, to the sperm duct being wrapped around the gut, despite the external organs being in their usual position. When flies mate, the male initially flies on top of the female, facing in the same direction, but then turns round to face in the opposite direction. This forces the male to lie on its back in order for its genitalia to remain engaged with those of the female, or the torsion of the male genitals allows the male to mate while remaining upright. This leads to flies having more reproduction abilities than most insects and at a much quicker rate. Flies come in great populations due ir ability to mate effectively and in a short period of time especially during the mating season.
The female lays her eggs as close to the food source as possible, and development is very rapid, allowing the larva to consume as much food as possible in a short period of time before transforming into the adult. The eggs hatch immediately after being laid, or the flies are ovoviviparous, with the larva hatching inside the mother. Larval flies, or maggot
Maggot
In everyday speech the word maggot means the larva of a fly ; it is applied in particular to the larvae of Brachyceran flies, such as houseflies, cheese flies, and blowflies, rather than larvae of the Nematocera, such as mosquitoes and Crane flies...
s, have no true legs, and little demarcation between the thorax and abdomen
Abdomen
In vertebrates such as mammals the abdomen constitutes the part of the body between the thorax and pelvis. The region enclosed by the abdomen is termed the abdominal cavity...
; in the more derived species, the head is not clearly distinguishable from the rest of the body. Maggots are limbless, or else have small proleg
Proleg
A Proleg is the small fleshy, stub structure found on the ventral surface of the abdomen of most larval forms of insects of the order Lepidoptera, though they can also be found on other larval insects such as sawflies and a few types of flies....
s. The eyes and antennae are reduced or absent, and the abdomen also lacks appendages such as cerci
Cercus
Cerci are paired appendages on the rear-most segments of many arthropods, including insects and arachnids but not crustaceans. Cerci often serve as sensory organs, but they may also be used as weapons or copulation aids, or they may simply be vestigial structures.Typical cerci may appear to be...
. This lack of features is an adaptation to a food-rich environment, such as within rotting organic matter, or as an endoparasite. The pupa
Pupa
A pupa is the life stage of some insects undergoing transformation. The pupal stage is found only in holometabolous insects, those that undergo a complete metamorphosis, going through four life stages; embryo, larva, pupa and imago...
e take various forms, and in some cases develop inside a silk cocoon. After emerging from the pupa, the adult fly rarely lives more than a few days, and serves mainly to reproduce and to disperse in search of new food sources.
Lepidoptera
In reproductive systemReproductive system
The reproductive system or genital system is a system of organs within an organism which work together for the purpose of reproduction. Many non-living substances such as fluids, hormones, and pheromones are also important accessories to the reproductive system. Unlike most organ systems, the sexes...
of butterflies and moths, the male genitalia are complex and unclear. In females there are three types of genitalia based on the relating taxa: monotrysian, exoporian, and dytresian. In the monotrysian type there is an opening on the fused segments of the sterna 9 and 10, which act as insemination and oviposition. In the exoporian type (in Hepaloidae and Mnesarchaeoidea) there are two separate places for insemination and oviposition, both occurring on the same sterna as the monotrysian type, 9/10. In most species the genitalia are flanked by two soft lobes, although they may be specialized and sclerotized in some species for ovipositing in area such as crevices and inside plant tissue. Hormones and the glands that produce them run the development of butterflies and moths as they go through their life cycle, called the endocrine system
Endocrine system
In physiology, the endocrine system is a system of glands, each of which secretes a type of hormone directly into the bloodstream to regulate the body. The endocrine system is in contrast to the exocrine system, which secretes its chemicals using ducts. It derives from the Greek words "endo"...
. The first insect hormone PTTH
Prothoracicotropic hormone
Prothoracicotropic hormone was the first insect hormone that was discovered. It was originally described simply as "brain hormone" by early workers such as Stefan Kopeć and Vincent Wigglesworth , who realized that ligation of the head of immature insects could prevent molting or pupation of the...
(Prothoracicotropic hormone) operates the species life cycle and diapause (see the relates section). This hormone is produced by corpora allata
Corpus allatum
The corpus allatum , in insect physiology, is an endocrine gland which generates juvenile hormone; as such, it plays a crucial role in metamorphosis. Surgical removal of the corpora allata can cause an immature larva to pupate at its next molt, resulting in a miniature adult...
and corpora cardiaca, where it is also stored. Some glands are specialized to perform certain task such as producing silk or producing saliva in the palpi. While the corpora cardiaca produce PTTH, the corpora allata also produces jeuvanile hormones, and the prothorocic glands produce moulting hormones.
In the digestive system, the anterior region of the foregut has been modified to form a pharyngial
Pharynx
The human pharynx is the part of the throat situated immediately posterior to the mouth and nasal cavity, and anterior to the esophagus and larynx. The human pharynx is conventionally divided into three sections: the nasopharynx , the oropharynx , and the laryngopharynx...
sucking pump as they need it for the food they eat, which are for the most part liquids. An esophagus
Esophagus
The esophagus is an organ in vertebrates which consists of a muscular tube through which food passes from the pharynx to the stomach. During swallowing, food passes from the mouth through the pharynx into the esophagus and travels via peristalsis to the stomach...
follows and leads to the posterior of the pharynx and in some species forms a form of crop. The midgut is short and straight, with the hindgut being longer and coiled. Ancestors of lepidopteran species, stemming from Hymenoptera
Hymenoptera
Hymenoptera is one of the largest orders of insects, comprising the sawflies, wasps, bees and ants. There are over 130,000 recognized species, with many more remaining to be described. The name refers to the heavy wings of the insects, and is derived from the Ancient Greek ὑμήν : membrane and...
, had midgut ceca, although this is lost in current butterflies and moths. Instead, all the digestive enzymes other than initial digestion, are immobilized at the surface of the midgut cells. In larvae, long-necked and stalked goblet cell
Goblet cell
Goblet cells are glandular simple columnar epithelial cells whose sole function is to secrete mucin, which dissolves in water to form mucus. They use both apocrine and merocrine methods for secretion....
s are found in the anterior and posterior midgut regions, respectively. In insects, the goblet cells excrete positive potassium
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
ions, which are absorbed from leaves ingested by the larvae. Most butterflies and moths display the usual digestive cycle, however species that have a different diet require adaptations to meet these new demands.
In the circulatory system
Circulatory system
The circulatory system is an organ system that passes nutrients , gases, hormones, blood cells, etc...
, hemolymph
Hemolymph
Hemolymph, or haemolymph, is a fluid in the circulatory system of some arthropods and is analogous to the fluids and cells making up both blood and interstitial fluid in vertebrates such as birds and mammals...
, or insect blood, is used to circulate heat in a form of thermoregulation
Thermoregulation
Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different...
, where muscles contraction produces heat which is transferred to the rest of the body when conditions are unfavorable. In lepidopteran species, hemolymph is circulated through the veins in the wings by some form of pulsating organ, either by the heart or by the intake of air into the trachea
Invertebrate trachea
The invertebrate trachea refers to the open respiratory system composed of spiracles, tracheae, and tracheoles that terrestrial arthropods have to transport metabolic gases to and from tissues....
. Air is taken in through spiracles along the sides of the abdomen and thorax supplying the trachea with oxygen as it goes through the lepidopteran's respiratory system
Respiratory system
The respiratory system is the anatomical system of an organism that introduces respiratory gases to the interior and performs gas exchange. In humans and other mammals, the anatomical features of the respiratory system include airways, lungs, and the respiratory muscles...
. There are three different tracheae supplying oxygen diffusing oxygen throughout the species body: The dorsal, ventral, and visceral. The dorsal tracheae supply oxygen to the dorsal musculature and vessels, while the ventral tracheae supply the ventral musculature and nerve cord, and the visceral tracheae supply the guts, fat bodies, and gonad
Gonad
The gonad is the organ that makes gametes. The gonads in males are the testes and the gonads in females are the ovaries. The product, gametes, are haploid germ cells. For example, spermatozoon and egg cells are gametes...
s.
See also
- Morphology (biology)Morphology (biology)In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
- Insect physiologyInsect physiologyInsect physiology includes the physiology and biochemistry of insect organ systems.Although diverse, insects are quite similar in overall design, internally and externally...
- Lepidoptera morphologyLepidoptera morphologyThe external morphology of Lepidoptera is the physiological structure of the bodies of insects belonging to the order Lepidoptera, also known as butterflies and moths. Lepidoptera are distinguished from other orders principally by the presence of scales on the external parts of the body and...
- Insect ecologyInsect ecologyInsect ecology is the scientific study of how insects, individually or as a community, interact with the surrounding environment or ecosystem....
- Insect flightInsect flightInsects are the only group of invertebrates known to have evolved flight. Insects possess some remarkable flight characteristics and abilities, still far superior to attempts by humans to replicate their capabilities. Even our understanding of the aerodynamics of flexible, flapping wings and how...
- InvertebrateInvertebrateAn invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...
- InsectInsectInsects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
- EntomologyEntomologyEntomology is the scientific study of insects, a branch of arthropodology...
- Prehistoric insect