Among the wide variety of commodities and materials which may be infested by psocids are the following: bagged nuts, bat guano, chocolate, fish meal, milk powder, museum specimens and books, oil seeds, processed cereals, pollen, salami, skin scales, Springbok biltong, stored cereal grains, sugar beet seeds, yeast and even damp plaster.

Although harmless to man, booklice are often confused with true lice and therefore regarded with alarm. As well as infesting foodstuffs in the home they may be encountered swarming over furnishings and walls, including newly plastered surfaces which are still damp. Clearly, materials of both animal and vegetable origin may be attacked but the insects show an undeniable preference for micro-organisms, including bacteria, yeasts, moulds and algae, and populations will develop more successfully in damp conditions where these thrive. This close association with micro-organisms results in these becoming entangled in their bodies and in this way the insects are instrumental in disseminating the organisms which cause spoilage.