A typical booklouse is small and soft-bodied, measuring about 1 to 2 mm or less in length, with a distinctive bulgy clypeus, an area above the mouthparts. Like all insects, the body is divided into three distinct parts: head, thorax, and abdomen. The head bears a pair of long and slender antennae, which extend past the abdomen, and mouthparts for chewing. Booklice vary in colour from translucent or pale white to grey or brown depending on species. Species that infest indoor spaces most often are usually wingless, unlike their outdoor counterparts.

Booklice cannot survive in low humidity and therefore only infest areas rife with moisture. In fact, booklouse infestations commonly occur in stored grains with a moisture content level of at least 14%. The pests are often associated with the presence of mould, which makes it imperative to look for signs of a booklouse infestation in warm, damp, dark places around the house where mould is likely to grow.