Embioptera
Encyclopedia
The order
Embioptera, commonly known as webspinners, are a small group of mostly tropical and subtropical insect
s, classified under the subclass Pterygota
. The order has also been referred to as Embiodea or Embiidina. The name Embioptera ("lively wings") comes from Greek
, embios meaning "lively" and pteron meaning "wing", a name that has not been considered to be particularly descriptive for this group of fliers. Perhaps instead referring to their remarkable speed of movement both forward and backward. The group probably first appeared during the Jurassic
and is well represented in Cretaceous
amber. The common name webspinner comes from the insects' ability to spin silk
from structures on their front legs. They use the silk to make a web-like pouch or gallery in which they live.
Over 360 embiopteran species have been described, along with estimates of around 2000 species being in existence today. There is some debate as to the exact phylogenetic classification of Embioptera, with the order having been classed as a sister group to both orders Zoraptera
, and Phasmatodea
, and there is continuing dispute today concerning the accuracy of these classifications.
The order is distributed all over the world, being found on every continent except Antarctica, with the highest density and diversity of species being located in tropical regions.
with chewing mandibles
. The compound eyes are kidney-shaped, there are no ocelli, and the antennae
are long, with up to 32 segments.
The body is cylindrical in form, adapted for the tubular galleries within which the insects live. The first segment of the thorax
is small and narrow, while the second and third are larger and broader, especially in the males, where they include the flight muscles. The wings, where present, occur as 2 pairs that are similar in size and shape: long and narrow, with relatively simple venation. These wings operate using basic hydraulics
; pre-flight, chambers within the wings fill with hemolymph
, making them rigid enough for use. On landing these chambers empty and wings become flexible, folding back against the body. Wings can also fold forwards over the body, and this, along with the flexibility allows easy movement through the narrow silk galleries without resulting in damage.
In both males and females the legs are short and sturdy, with an enlarged tarsomere
on the first pair, containing the silk-producing glands. The abdomen has ten segments, with a pair of cerci
on the final segment. These cerci are highly sensitive to touch, and allow the animal to navigate while moving backwards through the gallery tunnels, which are too narrow to allow the insect to turn round. Because morphology
is so similar between embiid species, it makes species identification extremely difficult. For this reason, the main form of taxonomic identification used in the past has been close observation of distinctive copulatory structures of males, (although this method is now thought by some entomologists and taxonomists as giving insufficient classification detail). Although males never eat during their life span, they do have mouthparts
similar to the females. These mouthparts are used to hold onto the female during copulation.
that resemble small, wingless adults (images right and below). After a short period of parental care, the nymphs undergo hemimetobolosis (moulting
into several immature stages before emerging as a fully grown adult after the last moult), moulting a total of four times before reaching adult form. Adult males never eat, and leave the home colony almost immediately to find a female and mate. Those males who can not fly will often mate with females in nearby colonies, meaning their chosen mates are often siblings or closely related. In some species, the female will eat the male after mating, but in any event, the male will not survive for long after mating. A few species are known to be parthenogenetic
, meaning they are able to produce viable offspring without fertilisation of eggs. This phemonenon occurs when a female is, for whatever reason, unable to find a male to mate with, thus giving her and her species reproductive security at all times.
. This particular kind of social behaviour involves the female embiid guarding her eggs and then caring for her young (right) for several days after hatching. In some species this parental care even involves the female feeding the nymphs with portions of chewed-up leaf litter and other food sources.
Subsociality is a trade-off for the female embiid, as the energy and time that is exerted into caring for her young is rewarded by giving them a much greater chance of surviving and carrying on her genetic lineage
. Some species do share galleries with more than one adult, however most groups consist of one adult female and her offspring.
. The silk is produced in spherical secretary glands in the tarsi
of the embiids enlarged forelimbs, and can be produced by both adults and larvae. Unlike Bombyx mori and other silk-producing (and spinning) members of both Lepidoptera
and Hymenoptera
, which only have one pair of silk glands per individual, some species of embiid are estimated to have up to 300 silk glands: 150 in each forelimb. These glands are linked to 'setae-like cuticular process called a silk ejector', and their exceedingly high numbers allow individuals to spin large amounts of silk very quickly, creating extensive galleries (see image below). The silk web is produced throughout all stages of the embiopteran lifespan, and requires very little energy output.
Webspinners continually extend their galleries into new food sources, and expand their existing galleries as they grow in size. The insects spin silk by moving their forelegs back and forth over the substrate, and rotating their bodies to create a cylindrical, silk-lined tunnel. Older galleries have multiple laminate layers of silk. Each gallery complex contains a number of individuals, often descended from a single female, and forms a complex maze-like structure, extending from a secure retreat into whatever vegetable food matter is available nearby. The size and complexity of the colony varies between species, and they can be very extensive in those species that live in hot and humid climates.
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
Embioptera, commonly known as webspinners, are a small group of mostly tropical and subtropical insect
Insect
Insects 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...
s, classified under the subclass Pterygota
Pterygota
Pterygota is a subclass of insects that includes the winged insects. It also includes insect orders that are secondarily wingless ....
. The order has also been referred to as Embiodea or Embiidina. The name Embioptera ("lively wings") comes from Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
, embios meaning "lively" and pteron meaning "wing", a name that has not been considered to be particularly descriptive for this group of fliers. Perhaps instead referring to their remarkable speed of movement both forward and backward. The group probably first appeared during the Jurassic
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
and is well represented in Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
amber. The common name webspinner comes from the insects' ability to spin silk
Silk
Silk is a natural protein fiber, some forms of which can be woven into textiles. The best-known type of silk is obtained from the cocoons of the larvae of the mulberry silkworm Bombyx mori reared in captivity...
from structures on their front legs. They use the silk to make a web-like pouch or gallery in which they live.
Over 360 embiopteran species have been described, along with estimates of around 2000 species being in existence today. There is some debate as to the exact phylogenetic classification of Embioptera, with the order having been classed as a sister group to both orders Zoraptera
Zoraptera
The insect order Zoraptera contains a single family, the Zorotypidae, which in turn contains one extant genus with 34 species, Zorotypus as well as 9 extinct species.-Phylogeny:...
, and Phasmatodea
Phasmatodea
The Phasmatodea are an order of insects, whose members are variously known as stick insects , walking sticks or stick-bugs , phasmids, ghost insects and leaf insects...
, and there is continuing dispute today concerning the accuracy of these classifications.
The order is distributed all over the world, being found on every continent except Antarctica, with the highest density and diversity of species being located in tropical regions.
Description
All webspinners have a remarkably similar body form, although they do vary in colouration and size. The majority of embiids are brown or black in colour, ranging through to a pink or reddish shades in some species, and range in size from 1.5 to 2 mm (0.0590551181102362 to 0.078740157480315 ). The body form of these insects is completely specialised for the silk tunnels and chambers in which they reside, being long, narrow and highly flexible. All the females and larvae are wingless, whereas males can be either winged or wingless depending on species. . The head has projecting mouthpartsInsect mouthparts
Insects exhibit a range of mouthparts, adapted to particular modes of feeding. The earliest insects had chewing mouthparts...
with chewing mandibles
Mandible (arthropod)
thumb|250px|The mandibles of a [[Bull ant]]The mandible of an arthropod is either of a pair of mouthparts used for biting, cutting and holding food. Mandibles are often simply referred to as jaws. Mandibles are present in the extant subphyla Myriapoda , Crustacea and Hexapoda...
. The compound eyes are kidney-shaped, there are no ocelli, and 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....
are long, with up to 32 segments.
The body is cylindrical in form, adapted for the tubular galleries within which the insects live. The first segment of the thorax
Thorax
The thorax is a division of an animal's body that lies between the head and the abdomen.-In tetrapods:...
is small and narrow, while the second and third are larger and broader, especially in the males, where they include the flight muscles. The wings, where present, occur as 2 pairs that are similar in size and shape: long and narrow, with relatively simple venation. These wings operate using basic hydraulics
Hydraulics
Hydraulics is a topic in applied science and engineering dealing with the mechanical properties of liquids. Fluid mechanics provides the theoretical foundation for hydraulics, which focuses on the engineering uses of fluid properties. In fluid power, hydraulics is used for the generation, control,...
; pre-flight, chambers within the wings fill with 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...
, making them rigid enough for use. On landing these chambers empty and wings become flexible, folding back against the body. Wings can also fold forwards over the body, and this, along with the flexibility allows easy movement through the narrow silk galleries without resulting in damage.
In both males and females the legs are short and sturdy, with an enlarged tarsomere
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 ,...
on the first pair, containing the silk-producing glands. The abdomen has ten segments, with a pair of 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...
on the final segment. These cerci are highly sensitive to touch, and allow the animal to navigate while moving backwards through the gallery tunnels, which are too narrow to allow the insect to turn round. Because morphology
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....
is so similar between embiid species, it makes species identification extremely difficult. For this reason, the main form of taxonomic identification used in the past has been close observation of distinctive copulatory structures of males, (although this method is now thought by some entomologists and taxonomists as giving insufficient classification detail). Although males never eat during their life span, they do have mouthparts
Insect mouthparts
Insects exhibit a range of mouthparts, adapted to particular modes of feeding. The earliest insects had chewing mouthparts...
similar to the females. These mouthparts are used to hold onto the female during copulation.
Life cycle
After mating, the female lays a single batch of eggs either within the existing gallery, or will find new territory to start a new colony. Here, the eggs hatch into nymphsNymph (biology)
In biology, a nymph is the immature form of some invertebrates, particularly insects, which undergoes gradual metamorphosis before reaching its adult stage. Unlike a typical larva, a nymph's overall form already resembles that of the adult. In addition, while a nymph moults it never enters a...
that resemble small, wingless adults (images right and below). After a short period of parental care, the nymphs undergo hemimetobolosis (moulting
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...
into several immature stages before emerging as a fully grown adult after the last moult), moulting a total of four times before reaching adult form. Adult males never eat, and leave the home colony almost immediately to find a female and mate. Those males who can not fly will often mate with females in nearby colonies, meaning their chosen mates are often siblings or closely related. In some species, the female will eat the male after mating, but in any event, the male will not survive for long after mating. A few species are known to be parthenogenetic
Parthenogenesis
Parthenogenesis is a form of asexual reproduction found in females, where growth and development of embryos occur without fertilization by a male...
, meaning they are able to produce viable offspring without fertilisation of eggs. This phemonenon occurs when a female is, for whatever reason, unable to find a male to mate with, thus giving her and her species reproductive security at all times.
Diet
The embiopteran diet varies between species, with available food sources changing with varying habitat. The nymphs and adult females are herbivorous, feeding on leaf litter, moss, bark and lichen. As stated above, adult males do not eat at all, meaning the majority die rapidly due to depleted energy resources (starvation).Social behaviour
Most, if not all embiopteran species, like many other species of insect, are gregarious, specifically displaying subsocialitySubsociality
Subsociality is a term used simply to refer to when an organism exhibits any form of parental behaviour. It is the most common and widespread form of sociality. In many species the mother, father or both parents either care for the young directly, or simply build a nest....
. This particular kind of social behaviour involves the female embiid guarding her eggs and then caring for her young (right) for several days after hatching. In some species this parental care even involves the female feeding the nymphs with portions of chewed-up leaf litter and other food sources.
Subsociality is a trade-off for the female embiid, as the energy and time that is exerted into caring for her young is rewarded by giving them a much greater chance of surviving and carrying on her genetic lineage
Lineage (evolution)
An evolutionary lineage is a sequence of species, that form a line of descent, each new species the direct result of speciation from an immediate ancestral species. Lineages are subsets of the evolutionary tree of life. Lineages are often determined by the techniques of molecular systematics.-...
. Some species do share galleries with more than one adult, however most groups consist of one adult female and her offspring.
Silk web production
Embiopterans produce a silk thread highly similar to that produced by the much better known silkworm Bombyx moriBombyx mori
The silkworm is the larva or caterpillar of the domesticated silkmoth, Bombyx mori . It is an economically important insect, being a primary producer of silk...
. The silk is produced in spherical secretary glands in the tarsi
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 ,...
of the embiids enlarged forelimbs, and can be produced by both adults and larvae. Unlike Bombyx mori and other silk-producing (and spinning) members of both 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 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...
, which only have one pair of silk glands per individual, some species of embiid are estimated to have up to 300 silk glands: 150 in each forelimb. These glands are linked to 'setae-like cuticular process called a silk ejector', and their exceedingly high numbers allow individuals to spin large amounts of silk very quickly, creating extensive galleries (see image below). The silk web is produced throughout all stages of the embiopteran lifespan, and requires very little energy output.
Galleries
The ‘galleries' produced by embiids are tunnels and chambers woven from the silk they produce. These woven constructions can be found on substrates such as rocks and the bark of trees, or in leaf litter. Some species camouflage their galleries by deccorating the outer layers with bits of leaf litter or other materials to match their surroundings (see image). The galleries are essential to their life cycle, maintaining moisture in their environment, plus offering protection from predators and elements while foraging, breeding and simply existing. The only occasion when an embiid will leave the gallery complex is when winged males fly out or wingless males walk out in search of a mate, or when females explore the area immediately surrounding them in search of a new food source. On detection of a potential predator or threat, the embiids retreat into their galleries, and some species have even been observed to 'play dead' until the threat is no longer present.Webspinners continually extend their galleries into new food sources, and expand their existing galleries as they grow in size. The insects spin silk by moving their forelegs back and forth over the substrate, and rotating their bodies to create a cylindrical, silk-lined tunnel. Older galleries have multiple laminate layers of silk. Each gallery complex contains a number of individuals, often descended from a single female, and forms a complex maze-like structure, extending from a secure retreat into whatever vegetable food matter is available nearby. The size and complexity of the colony varies between species, and they can be very extensive in those species that live in hot and humid climates.