The order Embioptera, commonly known as webspinners, are a small group of mostly tropical and subtropical insects, classified under the subclass Pterygota. The order has also been referred to as Embiodea or Embiidina. The name Embioptera ("lively wings") comes from Greek, εμβιος, embios meaning "lively" and πτερον, 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' unique 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.
|Embia major, male (left) and female (right)|
There are 2 suborders and 10 families:
Embides, Embidina, Embiida, Embiidina and Embiodea
All webspinners have a remarkably similar body form, although they do vary in colouration and size. The majority are brown or black in colour, ranging through to a pink or reddish shades in some species, and range in size from 15 to 20 mm (0.6 to 0.8 in). 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 nymphs are wingless, whereas adult males can be either winged or wingless depending on species. The head has projecting mouthparts 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 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 adult stage, they do have mouthparts similar to the females. These mouthparts are used to hold onto the female during copulation.
After molting and 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 nymphs that resemble small, wingless adults (images right and below). After a short period of parental care, the nymphs undergo hemimetabolosis (moulting into several instars before emerging as a fully grown adult after the last moult), molting 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 that 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 phenomenon 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.
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).
Most, if not all embiopteran species, like many other species of insect, are gregarious, specifically displaying subsociality. This particular kind of social behaviour involves the female 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, 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.
Embiopterans produce a silk thread highly similar to that produced by the much better known silkworm Bombyx mori. The silk is produced in spherical secretory 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.
The ‘galleries' produced by embiopterans 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 decorating 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 the elements while foraging, breeding and simply existing. The only occasion when an embiopteran 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.
Andesembiidae is a family of webspinners in the order Embioptera. There are at least two genera and about seven described species in Andesembiidae.Archembiidae
Archembiidae is a family of webspinners in the order Embioptera. There are at least 2 genera and about 12 described species in Archembiidae.Australembiidae
Australembiidae is a family of webspinners in the order Embioptera. There is at least one genus, Metoligotoma, in Australembiidae.Clothodidae
Clothodidae is a family of webspinners in the order Embioptera. There are about 5 genera and 18 described species in Clothodidae.Dicondylia
The Dicondylia are a taxonomic group (taxon) that includes all insects except the jumping bristletails (Archaeognatha). Dicondylia have a mandible attached with two hinges to the head capsule (dicondyl), in contrast to the original mandible with a single ball joint (monocondyl).Diradius
Diradius is a genus of webspinners in the family Teratembiidae. There are about 16 described species in Diradius.Embiidae
Embiidae is a family of webspinners in the order Embioptera. There are more than 20 genera and 80 described species in Embiidae.List of minor insects of Sri Lanka
Sri Lanka is a tropical island situated close to the southern tip of India. The invertebrate fauna is as large as it is common to other regions of the world. There are about 2 million species of arthropods found in the world, and still it is counting. So many new species are discover up to this time also. So it is very complicated and difficult to summarize the exact number of species found within a certain region.
The following list is about some minor insect orders recorded in Sri Lanka.Neoptera
Neoptera is a classification group that includes most orders of the winged insects, specifically those that can flex their wings over their abdomens. This is in contrast with the more basal orders of winged insects (the "Palaeoptera" assemblage), which are unable to flex their wings in this way.Oligotoma
Oligotoma is a genus of webspinners, insects in the order Embiidina, also known as Embioptera. The type species is Oligotoma saundersii and the type locality the Indian subcontinent. The males have wings but the females are flightless. Embiids are recognisable by the enlarged front tarsi, which contain a large number of silk glands that they use to spin the threads they use for building the tubes and galleries in which they live.Oligotoma saundersii
Oligotoma saundersii, commonly known as Saunders' embiid, is a species of webspinner, an insect in the order Embiidina, also known as Embioptera.Oligotomidae
Oligotomidae is a family of webspinners in the order Embioptera. There are about 6 genera and at least 40 described species in Oligotomidae.
They are known to be found in warmer regions of the Old World and in the Southwestern United States.Orthopterida
The Orthopterida is a superorder of the Polyneoptera that represents the extant orders Orthoptera (grasshoppers, crickets, and katydids), and Phasmatodea (stick insects and leaf insects). The Orthopterida also includes the extinct orders Titanoptera and Caloneurodea. There is general consensus of monophyly in this superorder, based on reduction of the second valvulae, an ovipositor derived from the gonoplac, and an enlarged precostal region on the forewing.
The two other superorders of the Polyneoptera are the Plecopterida, which represents the orders Plecoptera (stoneflies), Emboidea (Embioptera/Embiidina; webspinners), and Zoraptera (angel insects), and the Dictyoptera, which represents Blattodea (cockroaches & termites), and Mantodea (mantids). Two other orders, the Notoptera (ice-crawlers and gladiators) and Dermaptera (earwigs) are also placed in the Polyneoptera but outside the superorders discussed above.Paedembiidae
Paedembiidae is a family of webspinners in the order Embioptera. There are at least three genera and three described species in Paedembiidae.Pterygota
The Pterygota are a subclass of insects that includes the winged insects. It also includes insect orders that are secondarily wingless (that is, insect groups whose ancestors once had wings but that have lost them as a result of subsequent evolution).The pterygotan group comprises almost all insects. The insect orders not included are the Archaeognatha (jumping bristletails) and the Zygentoma (silverfishes and firebrats), two primitively wingless insect orders. Also not included are the three orders no longer considered to be insects: Protura, Collembola, and Diplura.Scelembiidae
Scelembiidae is a family of webspinners in the order Embioptera. There are about 16 genera and more than 40 described species in Scelembiidae.Spinneret
A spinneret is a silk-spinning organ of a spider or the larva of an insect. Some adult insects also have spinnerets, such as those borne on the forelegs of Embioptera. Spinnerets are usually on the underside of a spider's abdomen, to the rear. While most spiders have six spinnerets, some have two, four, or eight. They move independently and in concert.
Most spinnerets are not simple structures with a single orifice producing a single thread, but highly complex structures of many microscopic spigots, each producing one filament. This is important partly because it produces the necessary orientation of the protein molecules, without which the silk would be weak and useless. It also permits spiders to combine multiple filaments in different ways to produce many kinds of silk for special purposes.
Various species of spiders use silk extruded from spinnerets to build webs, to transfer sperm, to entrap insects by wrapping it around them, to make egg-cases, to catch the wind and fly (ballooning), etc. Some insect larvae (including silkworms) extrude silk to make a protective cocoon for their metamorphosis. The insects known as web spinners weave silken galleries for protection from predators and the elements while foraging and breeding.Observations suggesting that there might be silk-producing organs on the feet of the zebra tarantula (Aphonopelma seemanni) led to questions about the origins of spinnerets. It was hypothesised that spinnerets in spiders were originally used as climbing aids on the feet and evolved and were used for webmaking at a later time. However, these observations have since been challenged, as described in the main article on tarantulas.Teratembiidae
Teratembiidae is a family of insects in the order Embioptera, the web-spinners. They are distributed in the Nearctic, Neotropical and Afrotropic ecozones.Genera include:
Extant Embioptera families