When people see webs in the trees or in the leaf litter, they tend to think ‘spider’ but a surprising number of insects also build webs. These are not usually as beautiful or technically complicated as spider webs but they are still quite functional for providing protection for the insects and their young.
Web spinning is found in insects belonging to four different orders. The first, the small order Embioptera (containing only about 300 species), have the common name of webspinners as this is their most noticeable trait. Embids are small, inconspicuous, tropical insects that have silk glands on the tarsi of their front legs. They use this silk to create tunnels where numerous females and their young are protected from desiccation and predators. Another small, possibly closely related, order, the Psocopterans or booklice, also spin webs. Females of this small and primitive order of insects spin silk in which to hide their eggs.
A number of moths (Order Lepidoptera) also spin silk. Most of these moths belong to the family Yponomeutidae, which spin large thick silk webs in which the larvae are concealed and protected. Another family, the Psychidae are called ‘bagworms’ because they make silk bags to hold the larvae and the wingless females. The larvae stick sand, twigs and leaves to the bags. These bags can be tough and difficult to tear apart, which gives the otherwise vulnerable larvae much needed protection.
The most important insect silk spinner is of course, the silkworm moth, family Saturniidae. Admittedly this silk is formed to make capsules for the larvae rather than webs, but they must be mentioned because their silk is so much more economically important than spider silk, which may be stronger but has never been able to be economically exploited by humans. As with other spinning moths, the silk is spun by the larvae who make their own cocoons, rather than being made by the adult females as it is in the booklice and the embids. The moths also use glands in their mouths to make the silk rather than glands in the legs.
The last insect order that contains web spinners is the Hymenoptera (bees, wasps and ants). The so-called sawflies are actually related to wasps rather than flies, having four wings instead of the two that true flies sport. Sawfly larvae are also often mistaken for caterpillars of the order Lepidoptera because of superficial similarities. There are about 10,000 species of sawflies in the world, classified in the suborder Symphyta and many of these spin silk, using glands in the labia of their mouthparts. Their matted silken nests, filled with larval sawflies, can often be found at the bases of trees in late summer.
So next time you see a web in the leaf litter or in the foliage of a shrub or tree, have a closer look if you dare. It may be made by insects rather than spiders.