Booklice feeding. Booklice (Liposcelis bostrychophila) are very common, harmless household pests. They are approximately 1 millimetre long, and feed on mould caused by damp conditions, such as the microscopic moulds that grow in book-bindings or on damp cardboard, damp food such as cereals, and damp plaster. Booklice are parthenogenetic, and lay eggs on damp surfaces. They mature through four nymphal stages, taking about two weeks to become adult.