Springtail
Encyclopedia
Springtails form the largest of the three lineages of modern hexapods
that are no longer considered insect
s (the other two are the Protura and Diplura). Though the three orders are sometimes grouped together in a class called Entognatha
because they have internal mouthparts, they do not appear to be more closely related to one another than they all are to insects, which have external mouthparts.
Some DNA sequence
studies suggest that Collembola represent a separate evolutionary line
from the other Hexapoda
, but others disagree; this seems to be caused by widely divergent patterns of molecular evolution
among the arthropod
s. The adjustments of traditional taxonomic rank
for springtails reflects the incompatibility of traditional groupings with modern cladistics
: when they were included with the insects, they were ranked as an order
; as part of the Entognatha, they are ranked as a subclass
. If they are considered a basal lineage of Hexapoda, they are elevated to full class
status.
Members of Collembola are normally less than 6 millimetre (0.236220472440945 in) long, have six or fewer abdominal segments and possess a tubular appendage
(the collophore
or ventral tube) with eversible vesicles, projecting ventrally from the first abdominal segment. The Poduromorpha
and Entomobryomorpha
have an elongated body, while the Symphypleona
have a globular body. Collembola lack a tracheal
respiration system, which forces them to respire through a porous cuticle
, to the notable exception of Sminthuridae
which exhibit a rudimentary, although fully functional, tracheal system.
Most species have an abdominal, tail-like appendage, the furcula
, that is folded beneath the body to be used for jumping when the animal is threatened. It is held under tension by a small structure called the retinaculum
and when released, snaps against the substrate, flinging the springtail into the air. All of this takes place in as little as 18 milliseconds.
Arthropleona, Symphypleona
and occasionally also Neelipleona
. The Arthropleona were divided into two superfamilies, the Entomobryoidea
and the Poduroidea. But actually, these two and the Symphypleona form three lineages, each of which is equally distant from the other two. Thus, the Arthropleona are abolished in modern classifications, and their superfamilies are raised in rank accordingly, being now the Entomobryomorpha
and the Poduromorpha
. Technically, the Arthropleona are thus a partial junior synonym of the Collembola. The term "Neopleona" is essentially synonymous with Symphypleona
+ Neelipleona
.
The Neelipleona were originally seen as a particular advanced lineage of Symphypleona, based on the shared global body shape. But the global body of Neelipleona is realised in a completely different way than in Symphypleona. Subsequently, the Neelipleona
were considered as being derived from the Entomobryomorpha. But analysis of 18S and 28S rRNA sequence
data suggests that they form the most ancient lineage of springtails, which would explain their peculiar apomorphies.
Springtails are attested to since the Early Devonian. The fossil from , Rhyniella praecursor
, is the oldest terrestrial arthropod, and was found in the famous Rhynie chert
of Scotland
. Given its morphology resembles extant species quite well, the radiation of the Hexapoda
can be situated in the Silurian
, or more.
frequently found in leaf litter and other decaying material, where they are primarily detritivores and microbivores, and one of the main biological agents responsible for the control and the dissemination of soil microorganisms.
In sheer numbers, they are reputed to be one of the most abundant of all macroscopic animals, with estimates of 100,000 individuals per cubic meter of topsoil, essentially everywhere on Earth where soil and related habitats (moss
cushions, fallen wood
, grass
tufts, ant
and termite
nests) occur; only nematode
s, crustacean
s, and mite
s are likely to have global populations of similar magnitude, and each of those groups except mites is more inclusive: though taxonomic rank cannot be used for absolute comparisons, it is notable that nematodes are a phylum
and crustaceans a subphylum
. Most springtails are small and difficult to see by casual observation, but one springtail, the so-called snow flea
(Hypogastrura nivicola), is readily observed on warm winter days when it is active and its dark color contrasts sharply with a background of snow.
In addition, a few species routinely climb trees and form a dominant component of canopy faunas, where they may be collected by beating or insecticide fogging. These tend to be the larger (>2 mm) species, mainly in the genera Entomobrya and Orchesella
, though the densities on a per square meter basis are typically 1–2 orders of magnitude lower than soil populations of the same species. In temperate regions, a few species (e.g. Anurophorus spp., Entomobrya albocincta, Xenylla xavieri, Hypogastrura arborea) are almost exclusively arboreal. In tropical regions a single square meter of canopy habitat can support many species of Collembola.
The main ecological factor driving the local distribution of species is the vertical stratification of the environment: in woodland
a continuous change in species assemblages can be observed from tree canopies to ground vegetation
then to plant litter
down to deeper soil horizon
s. This is a complex factor embracing both nutritional and physiological requirements, together with probable species interactions. Some species have been shown to exhibit negative or positive gravitropism
, which adds a behavioural dimension to this still poorly understood vertical segregation.
As a group, springtails are highly sensitive to desiccation
, because of their tegumentary respiration
. The gregarious behaviour of Collembola, mostly driven by the attractive power of pheromones excreted by adults, gives more chance to every juvenile or adult individual to find suitable, better protected places, where desiccation could be avoided and reproduction rate could be kept at an optimum. Sensitivity to drought varies from species to species and increases during ecdysis
. Given that springtails are moulting repeatedly during their entire life (an ancestral character in Hexapoda
) they spend much time in concealed micro-sites where they can find protection against desiccation
and predation
during ecdysis
. The high humidity environment of many caves also favours springtails and there are numerous cave adapted species.
The horizontal distribution of springtail species is affected by environmental factors which act at the landscape scale, such as soil acidity, moisture
and light
. Requirements for pH
can be reconstructed experimentally. Altitudinal changes in species distribution can be at least partly explained by increased acidity at higher elevation. Moisture requirements explain why some species cannot live aboveground (vertical stratification), but also why some epigeal
springtails are always found in the vicinity of ponds and lakes, such as the hygrophilous Isotomurus palustris. Adaptive features, such as the presence of a fan-like wettable mucro, allow some species to move at the surface of water (Sminthurides aquaticus, Sminthurides malmgreni). Podura aquatica
, a unique representative of the family Poduridae (and one of the first springtails to have been described by Linnaeus), spends its entire life at the surface of water, its wettable eggs dropping in water until the non-wettable first instar hatches then surfaces.
In a variegated landscape, made of a patchwork of closed (woodland
) and open (meadow
s, cereal crops) environments, most soil
-dwelling species are not specialized and can be found everywhere, but most epigeal
and litter
-dwelling species are attracted to a particular environment, either forested or not. As a consequence of dispersal limitation, landuse change, when too rapid, may cause the local disappearance of slow-moving, specialist species.
Springtails are well known as pests of some agricultural crops. Sminthurus viridis
, the 'lucerne flea', has been shown to cause severe damage to agricultural crops, and is considered as a pest in Australia. Also Onychiuridae are known to feed on tubers and to damage them to some extent. However, by their capacity to carry spores of mycorrhizal fungi and mycorrhiza-helper bacteria on their tegument, soil springtails play a positive role in the establishment of plant-fungal symbioses and thus are beneficial to agriculture. They also contribute to controlling plant fungal diseases through their active consumption of mycelia and spores of damping-off and pathogenic fungi. It has been suggested that they could be reared to be used for the control of pathogenic fungi
in greenhouses and other indoor cultures.
Various sources and publications have suggested that some springtails may parasitize humans, but this is entirely inconsistent with their biology, and no such phenomenon has ever been scientifically confirmed, though it has been documented that the scales or hairs from collembolans can cause irritation when rubbed onto the skin. They may sometimes be abundant indoors in damp places such as bathrooms and basements, and incidentally found on one's person.
More often, claims of persistent human skin infection by springtails may indicate a neurological problem, such as Morgellons Syndrome
, or delusory parasitosis, a psychological rather than entomological problem. Researchers themselves may be subject to psychological phenomena. For example, a publication in 2004 claiming that springtails had been found in skin samples was later determined to be a case of pareidolia
; that is, no springtail specimens were actually recovered, but the researchers had digitally enhanced photos of sample debris to create images resembling small arthropod heads, which then were claimed to be springtail remnants. However, Hopkin reports one instance of an entomologist aspirating
an Isotoma
species and in the process accidentally inhaling some of their eggs, which hatched in his nasal cavity and made him quite ill until they were flushed out.
and chronic toxicity
tests have been performed by researchers, mostly using the parthenogenetic isotomid Folsomia candida. These tests have been standardized. More recently, avoidance tests have been also performed. They have been standardized, too. Avoidance tests are complementary to toxicity tests, but they also offer several advantages: they are more rapid (thus cheaper), more sensitive and they are environmentally more reliable, because in the real world Collembola may move far from pollution sources. It may be hypothesized that the soil could become locally depauperated in animals (and thus improper to normal use) while below thresholds of toxicity. Contrary to earthworm
s, and like many insects and molluscs, Collembola are very sensitive to herbicide
s and thus are threatened in no-tillage agriculture, which makes a more intense use of herbicides than conventional agriculture.
occurs through the clustered or scattered deposition of spermatophores by male
adults. Stimulation of spermatophore
deposition by female pheromones has been demonstrated in Sinella curviseta. Mating behaviour
can be observed in Symphypleona
. Among Symphypleona, males of Sminthurididae use a clasping organ located on their antenna
. Many collembolan species, mostly those living in deeper soil horizons, are parthenogenetic, which favours reproduction to the detriment of genetic diversity
and thereby to population
tolerance of environmental hazards. Parthenogenesis
(also called thelytoky
) is under the control of symbiotic bacteria
of the genus Wolbachia
, which live, reproduce and are carried in female reproductive organs and eggs of Collembola. Feminizing Wolbachia
species are widespread in arthropod
s and nematodes, where they co-evolved with most of their lineages
.
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...
that are no longer considered 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 (the other two are the Protura and Diplura). Though the three orders are sometimes grouped together in a class called Entognatha
Entognatha
The Entognatha is a class of ametabolous arthropods, which, together with insects, makes up the subphylum Hexapoda. Their mouthparts are entognathous, meaning they are retracted within the head. Entognatha are apterous, meaning they lack wings. The class contains three orders: Collembola , Diplura...
because they have internal mouthparts, they do not appear to be more closely related to one another than they all are to insects, which have external mouthparts.
Some DNA sequence
DNA sequence
The sequence or primary structure of a nucleic acid is the composition of atoms that make up the nucleic acid and the chemical bonds that bond those atoms. Because nucleic acids, such as DNA and RNA, are unbranched polymers, this specification is equivalent to specifying the sequence of...
studies suggest that Collembola represent a separate evolutionary line
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.-...
from the other 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...
, but others disagree; this seems to be caused by widely divergent patterns of molecular evolution
Molecular evolution
Molecular evolution is in part a process of evolution at the scale of DNA, RNA, and proteins. Molecular evolution emerged as a scientific field in the 1960s as researchers from molecular biology, evolutionary biology and population genetics sought to understand recent discoveries on the structure...
among the 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. The adjustments of traditional taxonomic rank
Taxonomic rank
In biological classification, rank is the level in a taxonomic hierarchy. Examples of taxonomic ranks are species, genus, family, and class. Each rank subsumes under it a number of less general categories...
for springtails reflects the incompatibility of traditional groupings with modern cladistics
Cladistics
Cladistics is a method of classifying species of organisms into groups called clades, which consist of an ancestor organism and all its descendants . For example, birds, dinosaurs, crocodiles, and all descendants of their most recent common ancestor form a clade...
: when they were included with the insects, they were ranked as an order
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...
; as part of the Entognatha, they are ranked as a subclass
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...
. If they are considered a basal lineage of Hexapoda, they are elevated to full 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...
status.
Description
Appendage
In invertebrate biology, an appendage is an external body part, or natural prolongation, that protrudes from an organism's body . It is a general term that covers any of the homologous body parts that may extend from a body segment...
(the collophore
Collophore
A collophore is a tube-like structure on the ventral side of the first abdominal segment of the body of a collembolan. It used to be believed that it served to stabilise the animal when it jumped by sticking to the surface on which it moved. However, the current scientific consensus is that it...
or ventral tube) with eversible vesicles, projecting ventrally from the first abdominal segment. The Poduromorpha
Poduromorpha
The order Poduromorpha is one of the three main groups of springtails , tiny hexapods related to insects. This group was formerly treated as a superfamily Poduroidea....
and Entomobryomorpha
Entomobryomorpha
The order Entomobryomorpha are one of the three main groups of springtails , tiny hexapods related to insects. This group was formerly treated as a superfamily Entomobryoidea....
have an elongated body, while the Symphypleona
Symphypleona
The order Symphypleona is one of the three main groups of springtails , tiny hexapods related to insects. When the springtails were still believed to be an order of insects, the Symphypleona were ranked as a suborder....
have a globular body. Collembola lack a tracheal
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....
respiration system, which forces them to respire through a porous cuticle
Cuticle
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...
, to the notable exception of Sminthuridae
Sminthuridae
Sminthuridae is a family of springtails of the order Symphypleona. Sminthurids are commonly referred to as globular springtails.- List of genera :There are ten genera within the Sminthuridae.* Arrhopalites Borner, 1906...
which exhibit a rudimentary, although fully functional, tracheal system.
Most species have an abdominal, tail-like appendage, the furcula
Furcula (Collembola)
The furcula, or furca, is a tail-like appendage shaped like a fork, found ventrally on the fourth abdominal segment of springtails. Present in most species dwelling the upper soil layers, it is used for jumping when the animal is threatened...
, that is folded beneath the body to be used for jumping when the animal is threatened. It is held under tension by a small structure called the retinaculum
Retinaculum
Occurs where in some places, groups of tendons from separate muscle pass under a band of connective tissueRetinaculum, from the Latin verb retinere , plural: retinacula may be:* In the wrist:** Flexor retinaculum of the hand...
and when released, snaps against the substrate, flinging the springtail into the air. All of this takes place in as little as 18 milliseconds.
Systematics and evolution
Traditionally, the springtails were divided into the ordersOrder (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...
Arthropleona, Symphypleona
Symphypleona
The order Symphypleona is one of the three main groups of springtails , tiny hexapods related to insects. When the springtails were still believed to be an order of insects, the Symphypleona were ranked as a suborder....
and occasionally also Neelipleona
Neelipleona
Neelipleona is a name given to some Hexapods of the subclass Collembola . While their taxonomic rank remains broadly settled as family Neelidae, Neelipleona has been described at Order or Suborder rank.-Taxonomic rank:...
. The Arthropleona were divided into two superfamilies, the Entomobryoidea
Entomobryoidea
The Entomobryoidea are a superfamily of springtails , tiny hexapods related to insects. In the modern sense, this group is placed in an order called Entomobryomorpha.This superfamily contains very characteristic species of springtails...
and the Poduroidea. But actually, these two and the Symphypleona form three lineages, each of which is equally distant from the other two. Thus, the Arthropleona are abolished in modern classifications, and their superfamilies are raised in rank accordingly, being now the Entomobryomorpha
Entomobryomorpha
The order Entomobryomorpha are one of the three main groups of springtails , tiny hexapods related to insects. This group was formerly treated as a superfamily Entomobryoidea....
and the Poduromorpha
Poduromorpha
The order Poduromorpha is one of the three main groups of springtails , tiny hexapods related to insects. This group was formerly treated as a superfamily Poduroidea....
. Technically, the Arthropleona are thus a partial junior synonym of the Collembola. The term "Neopleona" is essentially synonymous with Symphypleona
Symphypleona
The order Symphypleona is one of the three main groups of springtails , tiny hexapods related to insects. When the springtails were still believed to be an order of insects, the Symphypleona were ranked as a suborder....
+ Neelipleona
Neelipleona
Neelipleona is a name given to some Hexapods of the subclass Collembola . While their taxonomic rank remains broadly settled as family Neelidae, Neelipleona has been described at Order or Suborder rank.-Taxonomic rank:...
.
The Neelipleona were originally seen as a particular advanced lineage of Symphypleona, based on the shared global body shape. But the global body of Neelipleona is realised in a completely different way than in Symphypleona. Subsequently, the Neelipleona
Neelipleona
Neelipleona is a name given to some Hexapods of the subclass Collembola . While their taxonomic rank remains broadly settled as family Neelidae, Neelipleona has been described at Order or Suborder rank.-Taxonomic rank:...
were considered as being derived from the Entomobryomorpha. But analysis of 18S and 28S rRNA sequence
DNA sequence
The sequence or primary structure of a nucleic acid is the composition of atoms that make up the nucleic acid and the chemical bonds that bond those atoms. Because nucleic acids, such as DNA and RNA, are unbranched polymers, this specification is equivalent to specifying the sequence of...
data suggests that they form the most ancient lineage of springtails, which would explain their peculiar apomorphies.
Springtails are attested to since the Early Devonian. The fossil from , Rhyniella praecursor
Rhyniella praecursor
Rhyniella praecursor is a fossil springtail from the Rhynie chert formed during the Pragian stage of the Early Devonian; for some time it was believed to be the only hexapod from the Early Devonian...
, is the oldest terrestrial arthropod, and was found in the famous Rhynie chert
Rhynie chert
The Rhynie chert is an Early Devonian sedimentary deposit exhibiting extraordinary fossil detail or completeness . It is exposed near the village of Rhynie, Aberdeenshire, Scotland; a second unit, the Windyfield chert, is located some 700 m away...
of Scotland
Scotland
Scotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...
. Given its morphology resembles extant species quite well, the radiation of the 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...
can be situated in the Silurian
Silurian
The Silurian is a geologic period and system that extends from the end of the Ordovician Period, about 443.7 ± 1.5 Mya , to the beginning of the Devonian Period, about 416.0 ± 2.8 Mya . As with other geologic periods, the rock beds that define the period's start and end are well identified, but the...
, or more.
Distribution
Springtails are cryptozoaCryptozoa
Cryptozoa is the collective name for the small animals that permanently live under conditions with high relative humidity. Many of them can be found in any sample of wet soil; a large part of the cryptozoa has not yet been identified by science....
frequently found in leaf litter and other decaying material, where they are primarily detritivores and microbivores, and one of the main biological agents responsible for the control and the dissemination of soil microorganisms.
Moss
Mosses are small, soft plants that are typically 1–10 cm tall, though some species are much larger. They commonly grow close together in clumps or mats in damp or shady locations. They do not have flowers or seeds, and their simple leaves cover the thin wiry stems...
cushions, fallen wood
Wood
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...
, grass
Grass
Grasses, or more technically graminoids, are monocotyledonous, usually herbaceous plants with narrow leaves growing from the base. They include the "true grasses", of the Poaceae family, as well as the sedges and the rushes . The true grasses include cereals, bamboo and the grasses of lawns ...
tufts, 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...
and 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...
nests) occur; only nematode
Nematode
The nematodes or roundworms are the most diverse phylum of pseudocoelomates, and one of the most diverse of all animals. Nematode species are very difficult to distinguish; over 28,000 have been described, of which over 16,000 are parasitic. It has been estimated that the total number of nematode...
s, crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s, and mite
Mite
Mites, along with ticks, are small arthropods belonging to the subclass Acari and the class Arachnida. The scientific discipline devoted to the study of ticks and mites is called acarology.-Diversity and systematics:...
s are likely to have global populations of similar magnitude, and each of those groups except mites is more inclusive: though taxonomic rank cannot be used for absolute comparisons, it is notable that nematodes are a phylum
Phylum
In biology, a phylum The term was coined by Georges Cuvier from Greek φῦλον phylon, "race, stock," related to φυλή phyle, "tribe, clan." is a taxonomic rank below kingdom and above class. "Phylum" is equivalent to the botanical term division....
and crustaceans a subphylum
Subphylum
In life, a subphylum is a taxonomic rank intermediate between phylum and superclass. The rank of subdivision in plants and fungi is equivalent to subphylum.Not all phyla are divided into subphyla...
. Most springtails are small and difficult to see by casual observation, but one springtail, the so-called snow flea
Snow flea
Snow fleas are a species of dark blue springtail, Hypogastrura nivicola. They are often seen jumping about on the surface of snow on a warm winter day....
(Hypogastrura nivicola), is readily observed on warm winter days when it is active and its dark color contrasts sharply with a background of snow.
In addition, a few species routinely climb trees and form a dominant component of canopy faunas, where they may be collected by beating or insecticide fogging. These tend to be the larger (>2 mm) species, mainly in the genera Entomobrya and Orchesella
Orchesella
Orchesella is a genus of springtails belonging to the family Entomobryidae. It contains the following species :*Orchesella adriatica *Orchesella ainsliei *Orchesella albofasciata *Orchesella albosa *Orchesella alpa...
, though the densities on a per square meter basis are typically 1–2 orders of magnitude lower than soil populations of the same species. In temperate regions, a few species (e.g. Anurophorus spp., Entomobrya albocincta, Xenylla xavieri, Hypogastrura arborea) are almost exclusively arboreal. In tropical regions a single square meter of canopy habitat can support many species of Collembola.
The main ecological factor driving the local distribution of species is the vertical stratification of the environment: in woodland
Woodland
Ecologically, a woodland is a low-density forest forming open habitats with plenty of sunlight and limited shade. Woodlands may support an understory of shrubs and herbaceous plants including grasses. Woodland may form a transition to shrubland under drier conditions or during early stages of...
a continuous change in species assemblages can be observed from tree canopies to ground vegetation
Vegetation
Vegetation is a general term for the plant life of a region; it refers to the ground cover provided by plants. It is a general term, without specific reference to particular taxa, life forms, structure, spatial extent, or any other specific botanical or geographic characteristics. It is broader...
then to plant litter
Plant litter
Plant litter, leaf litter or tree litter is dead plant material, such as leaves, bark, needles, and twigs, that has fallen to the ground. Litter provides habitat for small animals, fungi, and plants, and the material may be used to construct nests. As litter decomposes, nutrients are released to...
down to deeper soil horizon
Soil horizon
A soil horizon is a specific layer in the land area that is parallel to the soil surface and possesses physical characteristics which differ from the layers above and beneath. Horizon formation is a function of a range of geological, chemical, and biological processes and occurs over long time...
s. This is a complex factor embracing both nutritional and physiological requirements, together with probable species interactions. Some species have been shown to exhibit negative or positive gravitropism
Gravitropism
Gravitropism is a turning or growth movement by a plant or fungus in response to gravity. Charles Darwin was one of the first to scientifically document that roots show positive gravitropism and stems show negative gravitropism. That is, roots grow in the direction of gravitational pull and stems...
, which adds a behavioural dimension to this still poorly understood vertical segregation.
As a group, springtails are highly sensitive to desiccation
Desiccation
Desiccation is the state of extreme dryness, or the process of extreme drying. A desiccant is a hygroscopic substance that induces or sustains such a state in its local vicinity in a moderately sealed container.-Science:...
, because of their tegumentary respiration
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...
. The gregarious behaviour of Collembola, mostly driven by the attractive power of pheromones excreted by adults, gives more chance to every juvenile or adult individual to find suitable, better protected places, where desiccation could be avoided and reproduction rate could be kept at an optimum. Sensitivity to drought varies from species to species and increases during 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...
. Given that springtails are moulting repeatedly during their entire life (an ancestral character in 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...
) they spend much time in concealed micro-sites where they can find protection against desiccation
Desiccation
Desiccation is the state of extreme dryness, or the process of extreme drying. A desiccant is a hygroscopic substance that induces or sustains such a state in its local vicinity in a moderately sealed container.-Science:...
and predation
Predation
In ecology, predation describes a biological interaction where a predator feeds on its prey . Predators may or may not kill their prey prior to feeding on them, but the act of predation always results in the death of its prey and the eventual absorption of the prey's tissue through consumption...
during 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...
. The high humidity environment of many caves also favours springtails and there are numerous cave adapted species.
Moisture
Humidity is the amount of moisture the air can hold before it rains. Moisture refers to the presence of a liquid, especially water, often in trace amounts...
and light
Light
Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...
. Requirements for pH
PH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
can be reconstructed experimentally. Altitudinal changes in species distribution can be at least partly explained by increased acidity at higher elevation. Moisture requirements explain why some species cannot live aboveground (vertical stratification), but also why some epigeal
Epigeal
Epigeal, epigean, epigeic and epigeous are biological terms describing an organism's activity above the soil surface.In botany, a seed is described as epigeal when the cotyledons of the germinating seed expand, throw off the seed shell and become photosynthetic above the ground...
springtails are always found in the vicinity of ponds and lakes, such as the hygrophilous Isotomurus palustris. Adaptive features, such as the presence of a fan-like wettable mucro, allow some species to move at the surface of water (Sminthurides aquaticus, Sminthurides malmgreni). Podura aquatica
Podura aquatica
The water springtail is a species of springtail, one of only four described species in the family Poduridae. It is an abundant species with a Holarctic distribution....
, a unique representative of the family Poduridae (and one of the first springtails to have been described by Linnaeus), spends its entire life at the surface of water, its wettable eggs dropping in water until the non-wettable first instar hatches then surfaces.
In a variegated landscape, made of a patchwork of closed (woodland
Woodland
Ecologically, a woodland is a low-density forest forming open habitats with plenty of sunlight and limited shade. Woodlands may support an understory of shrubs and herbaceous plants including grasses. Woodland may form a transition to shrubland under drier conditions or during early stages of...
) and open (meadow
Meadow
A meadow is a field vegetated primarily by grass and other non-woody plants . The term is from Old English mædwe. In agriculture a meadow is grassland which is not grazed by domestic livestock but rather allowed to grow unchecked in order to make hay...
s, cereal crops) environments, most soil
Soil
Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics...
-dwelling species are not specialized and can be found everywhere, but most epigeal
Epigeal
Epigeal, epigean, epigeic and epigeous are biological terms describing an organism's activity above the soil surface.In botany, a seed is described as epigeal when the cotyledons of the germinating seed expand, throw off the seed shell and become photosynthetic above the ground...
and litter
Litter
Litter consists of waste products such as containers, papers, wrappers or faeces which have been disposed of without consent. Litter can also be used as a verb...
-dwelling species are attracted to a particular environment, either forested or not. As a consequence of dispersal limitation, landuse change, when too rapid, may cause the local disappearance of slow-moving, specialist species.
Relationship with humans
Sminthurus viridis
Sminthurus viridis, the clover springtail or lucerne flea, is a hexapod belonging to the order Collembola . It is bright green with a roughly spherical body and often swarms in large numbers on living plants, especially Fabaceae including alfalfa...
, the 'lucerne flea', has been shown to cause severe damage to agricultural crops, and is considered as a pest in Australia. Also Onychiuridae are known to feed on tubers and to damage them to some extent. However, by their capacity to carry spores of mycorrhizal fungi and mycorrhiza-helper bacteria on their tegument, soil springtails play a positive role in the establishment of plant-fungal symbioses and thus are beneficial to agriculture. They also contribute to controlling plant fungal diseases through their active consumption of mycelia and spores of damping-off and pathogenic fungi. It has been suggested that they could be reared to be used for the control of pathogenic fungi
Pathogenic fungi
Pathogenic fungi are fungi that cause disease in humans or other organisms. The study of pathogenic fungi is referred to as medical mycology. Although fungi are eukaryotic organisms many pathogenic fungi are also microorganisms.-Candida:...
in greenhouses and other indoor cultures.
Various sources and publications have suggested that some springtails may parasitize humans, but this is entirely inconsistent with their biology, and no such phenomenon has ever been scientifically confirmed, though it has been documented that the scales or hairs from collembolans can cause irritation when rubbed onto the skin. They may sometimes be abundant indoors in damp places such as bathrooms and basements, and incidentally found on one's person.
More often, claims of persistent human skin infection by springtails may indicate a neurological problem, such as Morgellons Syndrome
Morgellons
Morgellons , is a name given in 2002 by Mary Leitao to a proposed condition characterized by a range of cutaneous symptoms including crawling, biting, and stinging sensations ; finding fibers on or under the skin; and persistent skin lesions...
, or delusory parasitosis, a psychological rather than entomological problem. Researchers themselves may be subject to psychological phenomena. For example, a publication in 2004 claiming that springtails had been found in skin samples was later determined to be a case of pareidolia
Pareidolia
Pareidolia is a psychological phenomenon involving a vague and random stimulus being perceived as significant. Common examples include seeing images of animals or faces in clouds, the man in the moon or the Moon rabbit, and hearing hidden messages on records played in reverse...
; that is, no springtail specimens were actually recovered, but the researchers had digitally enhanced photos of sample debris to create images resembling small arthropod heads, which then were claimed to be springtail remnants. However, Hopkin reports one instance of an entomologist aspirating
Pooter
A Pooter is a device used in the collection of insects, crustaceans or other small, fragile organisms, usually for scientific purposes....
an Isotoma
Isotoma (animal)
Isotoma is a common genus of springtails, the type genus of the family Isotomidae, containing the following species:*Isotoma acrea Wray, 1953*Isotoma agrelli Delamare, 1950*Isotoma alaskana Christiansen & Bellinger, 1980...
species and in the process accidentally inhaling some of their eggs, which hatched in his nasal cavity and made him quite ill until they were flushed out.
Ecotoxicology laboratory animals
Springtails are currently used in laboratory tests for the early detection of soil pollution. AcuteAcute toxicity
Acute toxicity describes the adverse effects of a substance that result either from a single exposure or from multiple exposures in a short space of time...
and chronic toxicity
Chronic toxicity
Chronic toxicity is a property of a substance that has toxic effects on a living organism, when that organism is exposed to the substance continuously or repeatedly. Compared with acute toxicity.Two distinct situations need to be considered:...
tests have been performed by researchers, mostly using the parthenogenetic isotomid Folsomia candida. These tests have been standardized. More recently, avoidance tests have been also performed. They have been standardized, too. Avoidance tests are complementary to toxicity tests, but they also offer several advantages: they are more rapid (thus cheaper), more sensitive and they are environmentally more reliable, because in the real world Collembola may move far from pollution sources. It may be hypothesized that the soil could become locally depauperated in animals (and thus improper to normal use) while below thresholds of toxicity. Contrary to earthworm
Earthworm
Earthworm is the common name for the largest members of Oligochaeta in the phylum Annelida. In classical systems they were placed in the order Opisthopora, on the basis of the male pores opening posterior to the female pores, even though the internal male segments are anterior to the female...
s, and like many insects and molluscs, Collembola are very sensitive to herbicide
Herbicide
Herbicides, also commonly known as weedkillers, are pesticides used to kill unwanted plants. Selective herbicides kill specific targets while leaving the desired crop relatively unharmed. Some of these act by interfering with the growth of the weed and are often synthetic "imitations" of plant...
s and thus are threatened in no-tillage agriculture, which makes a more intense use of herbicides than conventional agriculture.
Reproduction
Sexual reproductionSexual reproduction
Sexual reproduction is the creation of a new organism by combining the genetic material of two organisms. There are two main processes during sexual reproduction; they are: meiosis, involving the halving of the number of chromosomes; and fertilization, involving the fusion of two gametes and the...
occurs through the clustered or scattered deposition of spermatophores by male
Male
Male refers to the biological sex of an organism, or part of an organism, which produces small mobile gametes, called spermatozoa. Each spermatozoon can fuse with a larger female gamete or ovum, in the process of fertilization...
adults. Stimulation of spermatophore
Spermatophore
A spermatophore or sperm ampulla is a capsule or mass created by males of various animal species, containing spermatozoa and transferred in entirety to the female's ovipore during copulation...
deposition by female pheromones has been demonstrated in Sinella curviseta. Mating behaviour
Courtship
Courtship is the period in a couple's relationship which precedes their engagement and marriage, or establishment of an agreed relationship of a more enduring kind. In courtship, a couple get to know each other and decide if there will be an engagement or other such agreement...
can be observed in Symphypleona
Symphypleona
The order Symphypleona is one of the three main groups of springtails , tiny hexapods related to insects. When the springtails were still believed to be an order of insects, the Symphypleona were ranked as a suborder....
. Among Symphypleona, males of Sminthurididae use a clasping organ located on their antenna
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....
. Many collembolan species, mostly those living in deeper soil horizons, are parthenogenetic, which favours reproduction to the detriment of genetic diversity
Genetic diversity
Genetic diversity, the level of biodiversity, refers to the total number of genetic characteristics in the genetic makeup of a species. It is distinguished from genetic variability, which describes the tendency of genetic characteristics to vary....
and thereby to population
Population
A population is all the organisms that both belong to the same group or species and live in the same geographical area. The area that is used to define a sexual population is such that inter-breeding is possible between any pair within the area and more probable than cross-breeding with individuals...
tolerance of environmental hazards. Parthenogenesis
Parthenogenesis
Parthenogenesis is a form of asexual reproduction found in females, where growth and development of embryos occur without fertilization by a male...
(also called thelytoky
Thelytoky
Thelytoky comes from the Greek thely, meaning "female", and tokos, meaning "birth". Thelytokous parthenogenesis is a type of parthenogenesis in which females are produced from unfertilized eggs. It is rare in the animal kingdom and has only been reported in about 1500 species...
) is under the control of symbiotic 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...
of the genus Wolbachia
Wolbachia
Wolbachia is a genus of bacteria which infects arthropod species, including a high proportion of insects , as well as some nematodes. It is one of the world's most common parasitic microbes and is possibly the most common reproductive parasite in the biosphere...
, which live, reproduce and are carried in female reproductive organs and eggs of Collembola. Feminizing Wolbachia
Wolbachia
Wolbachia is a genus of bacteria which infects arthropod species, including a high proportion of insects , as well as some nematodes. It is one of the world's most common parasitic microbes and is possibly the most common reproductive parasite in the biosphere...
species are widespread 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 and nematodes, where they co-evolved with most of their lineages
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.-...
.