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.
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 birds' nests. Most of
these outdoor species are fully winged. |