Psocoptera (Barklice)

Psocoptera are a group of insects commonly known as booklice, barklice or barkflies. They are small, scavenging insects feeding primarily on fungi, algae, lichen, and organic detritus in nature, but in the domestic setting are known to feed on starch-based items like grains, wallpaper glue and book bindings.

They have chewing mandibles, and the central lobe of the maxilla is modified into a slender rod, which is used to brace the insect while it scrapes up detritus with its mandibles. They have a swollen forehead, pair of large compound eyes, and three simple eyes. Their bodies are soft with a segmented abdomen. Some species spin silk from glands in their mouth and colonise large sections of trunk and branches in dense silk.

Some psocids have small ovipositors up to 1.5 times as long as the hindwings. Their wings are usually simple in venation, with few cross-veins. The wings, if present, are held tent-like over the body and legs are slender and adapted for jumping. The abdomen has nine segments, with no cerci.

There is often considerable variation in the appearance of individuals within the same species, which includes being wingless or having no ovipositors, or even a differently shaped thorax. The significance of such changes is uncertain.

Psocids lay their eggs in minute crevices or on foliage, although a few species give birth to live young with the young being born as miniature, wingless versions of the adult. These nymphs usually molt six times before reaching full adulthood.

Psocids are of little economic importance as only some species are common pests of stored products, with the majority being forest insects with little to no contact with humans.