Psocids, Barklice, and Book Lice: Psocoptera

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BOOK LOUSE (Liposcelis bostrychophila): SPECIES ACCOUNTS


Most psocids (SO-sids) are small, ranging from 0.04 to 0.4 inches (1 to 10 millimeters) in length. They are usually brownish or whitish with black markings, but some tropical species are brightly colored with distinctive markings. The large and distinctive head has small to bulging compound eyes, with each eye made up of multiple lenses. The antennae (an-TEH-nee), or sense organs, are long and threadlike. The chewing mouthparts are directed downward and include parts that are sharp and pointed. The front of the head is usually swollen to make room inside for special muscles that control the part of the mouth known as the sucking pump. The thorax or midsection, especially the first segment, is usually narrower than the head or abdomen. Most adult psocids have four wings that are fully developed and are held like a roof over the body when at rest. Some species have wings that are reduced in size or absent altogether. The legs are usually slender, but in some species the back legs are swollen to help with jumping or crawling backward. The relatively large abdomen is eleven-segmented.


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 spend their time living alone. However, the larvae (LAR-vee), or young of an animal that must change form before becoming adults, of some species gather together to form colonies. Some species produce silk to make nests of various shapes and sizes. These nests may have one to many individuals living inside. Sound production in adult psocids is widely known and is thought to be a part of their courtship behavior.


Warm, damp homes, offices, and other buildings are perfect habitats for book lice. They forage for food in cellars, furniture stuffing, and inside food storage areas. Sometimes they will even eat the glue behind peeling wallpaper. They are particularly fond of libraries, nibbling the glue used in book bindings as well as the funguses that grow on the pages of books. Their feeding activities can cause great damage to old and rare books and papers.

Most psocids reproduce by mating, with males transferring sperm or sperm packets directly into the reproductive organs of the female. However, reproduction by parthenogenesis (PAR-thuh-no-JEH-nuh-sihs), the development of young from unfertilized eggs, is widespread. Parthenogenetic species produce only females. Eggs are laid singly or in groups. They are placed in the open, covered with silk webbing or with psocid waste material. A few species are viviparous (VAI-vih-pe-rus), or give live birth. The larvae hatch from eggs using a specialized egg-burster. The egg-burster is a bladelike or sawlike structure on the head that cuts through the eggshell as the young larva rocks back and forth inside. The larvae closely resemble the adults but lack wings and are unable to reproduce. They usually molt, or shed their exoskeletons or hard outer coverings, four or five times in four to six weeks before reaching adulthood. Some species molt only three or four times.


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.

BOOK LOUSE (Liposcelis bostrychophila): SPECIES ACCOUNTS

Physical characteristics: Book lice are small, about 0.04 inches (1 millimeter) in length. They are wingless, somewhat flattened, and are pale brown in color. Each compound eye is made up of seven lenses.

Geographic range: They are found on all continents.

Habitat: Book lice are commonly found in homes and businesses where foods are stored. They also occur in the wild in the nests of birds and other animals.

Diet: They eat funguses and other bits of plant and animal materials.

Behavior and reproduction: Different populations vary in size, color, egg production, and tolerance to insecticides.

Reproduction is by parthenogenesis only. Eggs are laid singly or in small batches and covered with a powdery dust. The larvae molt four times before reaching adulthood.

Book lice and people: Book lice are considered a nuisance when they infest stored foods and libraries. Their presence in the home may also set off allergy and asthma attacks.

Conservation status: This species is not endangered or threatened. ∎



Mockford, E. L. "North American Psocoptera." In Flora & Fauna Handbook, No. 10. Gainesville, FL: Sandhill Crane Press, 1993.

Tavolacci, J., editor. Insects and Spiders of the World. Volume 2: Beetle-Carpet Beetle. New York: Marshall Cavendish, 2003.

Web sites:

Psocids as Pests. (accessed on October 5, 2004).

"Psocoptera. Book lice." Ecowatch. (accessed on October 5, 2004)

Psocoptera. Psocids, barklice, booklice. (accessed on October 5, 2004).