Psocodea

Psocodea is a taxonomic group of insects comprising the bark lice, book lice and parasitic lice. It was formerly considered a superorder, but is now generally considered by entomologists as an order. Despite the greatly differing appearance of parasitic lice (Phthiraptera), they are believed to have evolved from within the former order Psocoptera, which contained the bark lice and book lice, now found to be paraphyletic. They are often regarded as the most primitive of the hemipteroids. Psocodea contains around 11,000 species, divided among four suborders and more than 70 families. They range in size from 1–10 millimetres (0.04–0.4 in) in length.

The species known as booklice received their common name because they are commonly found amongst old books—they feed upon the paste used in binding. The barklice are found on trees, feeding on algae and lichen.