Small, soft-bodied insects with two pairs of membranous wings or
wingless. When at rest, most winged species hold their wings steeply roof-wise over the body. Head quite broad, with long
filamentous antennae and biting mouthparts. Eyes often large and protruding from the sides of the head. Legs with two or
three tarsal segments. Cerci absent. Metamorphosis simple, usually with six nymphal stages before reaching maturity, although
some wingless forms may have fewer stages. This is a relatively small Order with about 2,000 described species worldwide.
Over 90 species have been recorded from Britain, but only about 50 of these are known to occur naturally. The others are
mostly casual imports, often in stored products, and some are recorded only from single specimens found in warehouses or ships
holds. The best known psocids are the very small, wingless species commonly known as Booklice or Dustlice, which often infest
houses, libraries, food stores, warehouses and other buildings. However, the majority of species, often called Barklice, live
outside on tree bark, leaves, fences, stone walls and in old bird nests. Most of these outdoor species are fully winged.