Web spinners

Embiidina (= Embioptera, Embiodea).

Embiids.

While the majority of embiids (Ross 1970) are secretive and unknown except to the specialist, some species are very conspicuous because of the extensive webs they construct on tree trunks and limbs. At times, almost the entire boles of large trees may be covered with these filmy mats that show little organized structure save branching galleries. It is within these passages that the web spinners live, and they may be seen through the walls as they move back and forth.

Figure 5.14 INSECTS OF VARIOUS ORDERS, (a) Web spinner (Clothoda urichi, Clothodidae). (b) Barklouse (Poecilopsocus iridescens, Psocidae). (c) Booklouse (Liposcelis bostrychophila, Ijpuscelidae). (d) Black hunter (Leptothrips mali, Phlaeothripidae). (e) Greenhouse thrip (Heliothrips haemorrhoidalis, Thripidae).

Figure 5.14 INSECTS OF VARIOUS ORDERS, (a) Web spinner (Clothoda urichi, Clothodidae). (b) Barklouse (Poecilopsocus iridescens, Psocidae). (c) Booklouse (Liposcelis bostrychophila, Ijpuscelidae). (d) Black hunter (Leptothrips mali, Phlaeothripidae). (e) Greenhouse thrip (Heliothrips haemorrhoidalis, Thripidae).

The silk forming these labyrinths issues from glands in the basal segment of the forelegs. This segment is inflated in nymphs and adults and clearly distinguishes these insects from all others. Other identifying features are the usually complex, asymmetrical genitalia of the male, and, in alate species (many lack wings altogether or have only small alar buds), wings that have pigmented bands along the veins alternating with clear stripes. Web spinners are mandibulate with filiform antennae with numerous segments.

A web spinner's body is elongate and very supple. Flexible wings and short legs allow it to move with great ease, even backward as easily as forward, through its galleries. These insects are well protected by their ability to retreat deeply within their silken tent, which not only forms a physical barrier to entry by such primary enemies as ants but hides them from the eyes of larger predators.

Embiids are gregarious. Typical colonies consist of a single female living in the midst of its brood (Edgerly 1988). Although they •hare in common a complex of galleries, i they should be considered subsocial, for I they lack castes, division of labor, or other Icharacteristics of the true insect societies. |At least one Trinidadian web spinner, jCiot/wda urichi (fig. 5.14a), is facultatively leommunal (Edgerly 1987). p The food of embiids consists of bark, ■pad leaves, moss, lichens, and other or ganic matter of plant origin that they find in their immediate habitat.

Although Latin America is a major center of evolution of the order, the embiid fauna has been studied only to a limited degree (Ross 1943, 1944, 1984). Several hundred may actually exist, but only about 150 species in five families are presently described. The family Clothodidae is confined to South America (including Trinidad and Panama). Chelicera (Anisembiidae) is the dominant genus, with many species in semiarid environments.

Web spinners are found in widely varied habitats, from humid forests to deserts. One species is known from the Galápagos Islands, another from the fog-dampened lomas of coastal Peru (Ross 1966). Around human habitations, the most common is Oligotoma saundersii, a "weed species," spread by man from India. Its males are attracted to lights.

References

Edgerly, J. S. 1987. Colony composition and some costs and benefits of facultatively communal behavior in a Trinidadian webspinner Clothoda urichi (Embiidina: Clothodidae). En-tomol. Soc. Amer. Ann. 80: 29-34. Edgerly, J. S. 1988. Maternal behavior of a webspinner (Order Embiidina): Mother-nymph associations. Ecol. Entomol. 13: 263-272. Ross, E. S. 1943. Métodos de recoleción, crianza y estudio de los Embiópteros (Ins. Embioptera). Rev. Entomol. 14: 441-446. Ross, E. S. 1944. A revision of the Embioptera of the New World. U.S. Natl. Mus. Proc. 94: 401-504.

Ross, E. S. 1966. A new species of Embioptera from the Galápagos Islands. Calif. Acad. Sci. Proc. (Ser. 4) 34: 499-504. Ross, E. S. 1970. Biosystematics of the Embioptera. Ann. Rev. Entomol. 15: 157-171. Ross, E. S. 1984. A classification of the Embi-idina of Mexico with descriptions of new taxa. Calif. Acad. Sci. Occ. Pap. 140: 1-50.

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