Barklice Psocids and Book Lice: Psocoptera

Psocids are found on all continents, including Antarctica. There are 4,408 species of psocids worldwide, mostly in the tropics. About 260 species occur in the United States and Canada.

Psocids live in a wide variety of habitats on land. In spite of the common names that include the word "louse," these insects do not live on other animals. They are most common on dead or living leaves, on stone or bark surfaces, and in leaf litter. Some species prefer living in caves; others are known to bore into wood. A few species of psocids are common in homes and buildings, especially where food is stored.

Psocids eat lichen (LIE-kuhn) or mosses, funguses, and other bits of plant and animal tissues. They will even feed on the skin flakes of humans and their animals. Some species scavenge dead insects or eat their eggs.

Most psocids live in the wild and are seldom, if ever, noticed by humans. However, species common in homes are often considered household pests. They can reproduce rapidly under warm, humid conditions and will become serious pests in foods stored in cupboards and pantries. These species are known to cause sneezing, coughing, itching, and rashes, as well as asthma attacks in sensitive people.

No species of psocids is endangered or threatened. Still, many species, especially those living only on single islands or in caves, could easily become threatened by habitat destruction due to bad weather or human activities.