These fast moving, minute, cream-coloured or light brown insects, only 1mm long, occur in small numbers in many premises. There are several species, known collectively as Psocids. All have soft bodies. Very few species have wings. They are not related to the parasitic lice (see Lice).
Sticky, pearl-coloured eggs are cemented to damp surfaces and, instead of a larval stage, the insect matures through four recognisable nymphal stages, taking about a fortnight in total.
The adult booklice are believed to feed on microscopic moulds that grow on the glue of book-bindings or on damp cardboard, damp food (especially cereals) or on the surfaces of plaster, leather or wood inside buildings.
They can occur in huge numbers in new properties where the plaster is still damp. One species of booklouse produces an audible tapping noise by banging its abdomen against paper or wood.