Box 9.5. Embiidina or Embioptera (embiids, webspinners)
There are some 300 described species of embiids (perhaps up to an order of magnitude more remain undescribed) in at least eight families, worldwide. Small to moderately sized, they have an elongate, cylindrical body, somewhat flattened in males. The head is prognathous, and the compound eyes are reniform (kidney-shaped), larger in males than females; ocelli are absent. The antennae are multisegmented, and the mouthparts are mandibulate. The quadrate prothorax is larger than the meso- or metathorax. All females and some males are apterous, and, if present, the wings (illustrated here for Embia major, after Imms 1913) are characteristically soft and flexible, with blood sinus veins stiffened for flight by hemolymph pressure. The legs are short, with three-segmented tarsi; the basal segment of each fore tarsus is swollen and contains silk glands, whereas the hind femora are swollen with strong tibial muscles. The abdomen is 10-segmented, with only the rudiments of segment 11; the cerci comprise two segments and are responsive to tactile stimuli. The female external genitalia are simple, whereas the male genitalia are complex and asymmetrical.
During copulation, the male holds the female with his prognathous mandibles and/or his asymmetrical cerci. The eggs and early nymphal stages are tended by the female parent, and the immature stages resemble the adults except for their wings and genitalia. Embiids live gregariously in silken galleries, spun with the tarsal silk glands (present in all instars); their galleries occur in leaf litter, beneath stones, on rocks, on tree trunks (see Plate 4.1, facing here), or in cracks in bark and soil, often around a central retreat. Their food comprises litter, moss, bark, and dead leaves. The galleries are extended to new food sources, and the safety of the gallery is left only when mature males disperse to new sites, where they mate, do not feed, and sometimes are cannibalized by females (see Plate 4.2). Webspinners readily reverse within their galleries, for example when threatened by a predator.
