Embioptera

(invertebrate zoology) An order of silk-spinning, orthopteroid insects resembling the grasshoppers; commonly called the embiids or webspinners.

(Webspinners)

Class: Insecta

Order: Embioptera

Number of families: 8

Evolution and systematics

Fossil embiids date from the Oligocene, with controversial records from the Lower Permian of the Urals in Russia. The exact phylogenetic position of webspinners is uncertain, but they are considered orthopteroid insects, sharing some characters with earwigs (Dermaptera), stoneflies (Plecoptera), stick insects (Phasmatodea), zorapterans (Zoraptera), and termites (Isoptera). The order Embioptera (or Embiidina) includes eight living families with only 300 described species, although it is estimated that the true number of species is around 2,000.

Physical characteristics

Webspinners are small-to-medium-size insects, with lengths ranging from 0.06 to 0.78 in (1.5 to 20 mm). They have narrow, elongated bodies, which are usually brown or black, an anteriorly directed head with long filiform antennae, and short legs. Both larvae and adults can be easily recognized by their greatly swollen foretarsi. This enlarged foretarsi houses about 100 silk glands, which are used to spin silk galleries, inside which webspinners spent almost their entire life.

The ten-segmented embiid abdomen ends in two-articulated cerci, which are surrounded with sensory hairs and provide tactile orientation against the walls of the galleries, especially when webspinners run backward. Males have large compound eyes and asymmetric external genitalia, and lack wings in some species. When present, the wings have only a few veins, are flexible, and can be folded forward over the body at any point, allowing for reverse movement in the narrow galleries. Some veins are transformed into blood sinuses, which provide temporary stiffness to the wings when used for flight. Females always lack wings, have smaller compound eyes, and are usually larger than males. Larvae look like the adult female, and only male larvae that will develop into winged adult males have external wing buds. Eggs are elongated, with a rimmed, circular operculum.

Distribution

The bulk of the embiid diversity is found in the tropics worldwide, although some species extend into the southern United States and temperate regions of Europe. Embiids are usually absent or poorly represented on islands. Some species have spread through commerce and as a result are widely distributed.

Habitat

Embiids spin their silk galleries on exposed bark or rock surfaces in humid areas; hidden under bark flakes, stones, or leaf litter; and in crevices or cracks in the soil, rocks, or termite mounds. Their galleries can also be found in hanging moss in mountain rainforests.

Behavior

With the exception of occasional dispersal, all embiid activity takes place inside the silk galleries. Webspinners are gregarious, with one or more adult females and their broods sharing a branched system of galleries, which they all spin and extend continuously. The galleries are just slightly wider than the body of the embiids, allowing their sensory body hairs to be in constant contact with the walls. Some species add vegetable detritus and frass to the galleries, providing additional cover and camouflage. Galleries are used as protected routes to food sources, to avoid desiccation, and as escape routes from predators. When an embiid is threatened, it rapidly retreats backward inside the labyrinth of silken tubes.

Feeding ecology and diet

Larvae and adult female embiids feed on vegetable matter, from live moss and lichens to dead leaves and bark. Adult males do not feed.

Reproductive biology

Males use their modified mandibles to hold the female's head during copulation. After mating, males soon die, and females lay a layer of eggs on a silken surface, which is used as a starting point for a new colony or an extension of an old one. Females show parental care, guarding their eggs and young larvae. In some species, females coat the eggs with feces, masticated vegetable matter, or leaf fragments; those in other species move the eggs about in the galleries. There are some known cases of parthenogenetic females, in which the young develop from unfertilized eggs. Development is through gradual metamorphosis.

Conservation status

No webspinner is listed by the IUCN.

Significance to humans

Webspinners are scarcely noticed by humans because of their secluded habits in galleries. They are of no economic importance, as they feed on dead vegetable matter in uncultivated areas.

Species accounts

Resources

Ross, E. S. "Embiidina (Embioptera, Webspinners)" In Encyclopedia of Insects, edited by V. H. Resh and R. T. Cardé. San Diego: Academic Press/Elsevier Science, 2003. ——. "Embioptera: Embiidina (Embiids, Web-Spinners, Foot-Spinners)." In The Insects of Australia: A Textbook for Students and Research Workers. Vol. 1, 2nd edition, edited by CSIRO. Carlton, Australia: Melbourne University Press, 1991. ——. "Order Embiidina (Embioptera)." In Immature Insects. Vol. 1, edited by F. W. Stehr. Dubuque, IA: Kendall/Hunt Publishing, 1987. ——. "Web Spinners of Panama (Embiidina)." In Insects of Panama and Mesoamerica, edited by D. Quintero and A. Aiello. New York: Oxford University Press, 1992.

Edgerly, J. S. "Maternal Behavior of a Webspinner (Order Embiidina)." Ecological Entomology 12 (1987): 1–11.

Ross, E. S. "Embia. Contributions to the Biosystematics of the Insect Order Embiidina." Part 1, "Origin, Relationships and Integumental Anatomy of the Insect Order Embiidina." Occasional Papers of the California Academy of Sciences 149 (2000): 1–53. ——. "Embia. Contributions to the Biosystematics of the Insect Order Embiidina." Part 2, "A Review of the Biology of Embiidina." Occasional Papers of the California Academy of Sciences 149 (2000): 1–36.

Valentine, B. D. "Grooming Behavior in Embioptera and Zoraptera (Insecta)." Ohio Journal of Science 86 (1986): 150–152.

[Article by: Natalia von Ellenrieder, PhD]

A peculiar order of silk-spinning, orthopteroid insects related to termites, commonly called the embiids or web spinners. This order comprises about 1000 species which are chiefly tropical in distribution. The body is linear and supple. The legs are short with three-segmented tarsi. The forelegs are adapted for spinning silk, and the hindlegs for reverse locomotion. Metamorphosis is incomplete. The females are neoteinic and wingless (apterous). Males are usually winged (alate), but in certain genera and species they are apterous. The wings are subequal and elongate. The wings are flexible when in repose and folded over the back, but are stiffened when extended for flight by the blood pressure in the saclike veins. Flight is a poorly directed, whirling flutter.

The silk galleries, which constitute a safe shelter for all embiid activities except adult dispersal, radiate on or in the food supply which also constitutes the habitat and consists of bark, lichens, moss, dead leaves, or grass. Many individuals, usually the brood of one female, may occupy one gallery system. See also Insecta; Orthoptera.

The noun has one meaning:

Meaning #1: web spinners
  Synonyms: order Embioptera, Embiodea, order Embiodea

Webspinner Fossil range: 199–0 Ma PreЄ Є O S D C P T J K Pg N Jurassic - Recent
Scientific classification
Kingdom: Animalia Phylum: Arthropoda Class: Insecta Subclass: Pterygota Infraclass: Neoptera Order: Embioptera Lameere, 1900
Families
There are 2 suborders and 10 families: Andesembiidae Anisembiidae Australembiidae Clothodidae Embiidae Embonychidae Notoligotomidae Oligotomidae Teratembiidae Sorellembiidae

Webspinners or embiids (order Embioptera) 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^[1] The name Embioptera (lively wings) comes from Greek, embio meaning lively and ptera meaning wings, and refers to the fluttery movement of wings that was observed in the first male specimen described.

The group probably first appeared during the Jurassic and is well represented in Cretaceous amber. All the females are wingless, and in some species also the males. Webspinners spin silk from structures on their front legs. They use the silk to make a weblike pouch or gallery in which they live. The galleries may be found in leaf litter, under rocks, or under bark.

The order contains only some 300 species, most of which are found only in tropical climates, although a small number of temperate species do exist.

Description

All webspinners have a remarkably similar body form, although they do vary in colouration and size. 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.^[2]

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, are long and narrow, with relatively simple venation. 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.^[2]

The female lays her eggs within the gallery, where they hatch into nymphs that resemble small, wingless adults. After a brief period of parental care, the nymphs moult a total of four times before reaching adulthood. Adult males never eat, and leave the home colony almost immediately to find a female and mate. In some species, the female then eats the male, but in any event, the male will not survive for long after mating. A few species are known to be parthenogenetic.^[2]

The nymphs and adult females are herbivorous, feeding on leaf litter, moss, bark and lichen.

Galleries

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.^[2]

References

1. ^ Borror, Triplehorn and Delong. An Introduction to the Study of Insects (sixth edition). page 247. Harcourt Brace College Publishers. 1989.
2. ^ ^{a b c d} Hoell, H.V., Doyen, J.T. & Purcell, A.H. (1998). Introduction to Insect Biology and Diversity, 2nd ed.. Oxford University Press. pp. 389-391. ISBN 0-19-510033-6. 

• Grimaldi, D. and Engel, M.S. (2005). Evolution of the Insects. Cambridge University Press. ISBN 0-521-82149-5. 

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