Key to Australian Freshwater and Terrestrial Invertebrates

Phylum Arthropoda
Subphylum Hexapoda
Class Insecta
Order Embioptera

Common names: web spinners, embiids

Overview

The Embioptera, or web spinners, are a small order of elongate, cylindrical insects that are rarely seen as they spend most of their lives within their silken galleries. Web spinners have short legs; the basal segments of their front tarsi are enlarged and contain silk glands. Females are all wingless (apterous) whereas males can be wingless, or fully (macropterous) or short-winged (brachypterous); both pairs of wings are membranous. Males are weak fliers and have to pump fluid (haemolymph) into their wing veins to stiffen them for flight; they generally only fly in search of a mate and may be attracted to light at night. Embiids have chewing (mandibulate) mouthparts, medium-length, segmented antennae and two short cerci at the end of the abdomen; in males the cerci are unequal in size and shape. Body length ranges from 4�15 mm.

Distribution and diversity

Web spinners are found worldwide, predominantly in tropical habitats but also in warm temperate regions. Around 200 embiopteran species have been described but an estimated 2,000 species may exist. Web spinners occur across Australia where the fauna comprises 26 described species in five genera and three families; estimates are given of over 65 species in total.

Life cycle

Adult male web spinners only live for a short time and those species with wings fly in search of mates. Sperm transfer is direct. Females either stay in an established gallery or disperse to begin a new colony. Eggs are laid into silk-enclosed chambers of chewed up bark and leaf fragments and the female protects her eggs and nymphs (brood care). When the nymphs hatch they immediately begin to spin silken galleries of their own and live together, the mother forming gregarious family groups of one or more adult females and their offspring. The nymphs resemble small wingless adults; juvenile males of winged species have wing buds.

Feeding

Web spinner nymphs and adults feed on live and decaying plant matter such as leaves, bark, litter, mosses and lichens. They constantly extend their silken galleries to acquire new food sources. The short-lived adult males usually do not feed.

Ecology

Web spinners are most noted for their ability to produce silk. They use it to produce narrow silken tubes that form the galleries they inhabit. In more humid climates, embiopterans construct their galleries exposed on bark and rock surfaces, whereas in dry regions, galleries are more likely to be constructed in more sheltered locations such as under rocks or bark, in cracks in the soil, in plant litter or in old wood, such as fence posts. In very moist environments, such as tropical forests, they spin their galleries among hanging moss. Web spinners spend their entire lives within their silken galleries, only leaving to disperse. When disturbed by predators, such as ants, they can rapidly run backward into the silken tunnels.