Booklice

Classification

Common names: Booklice, psocids

Scientific name. Family: Liposcelididae (booklice)

Order: Psocodea (booklice, barklice, and parasitic lice)

Distribution

Booklice are found worldwide. 

Description and Identification

Booklice are small (0.4–0.8 in, 1–2 mm), soft-bodied, wingless insects. They are dosoventrally flattened, so are wider than thick. Most booklice are light to dark tan in color, but can be grey, dark brown, orange-brown, or nearly clear (especially young individuals). The head is wide and has a large clypeus, which appears as a large “nose.” The femora are flattened and wide.

Because of their flattened appearance, booklice are sometimes confused for bedbugs. However, bed bugs are usually larger (newly hatched bedbugs are approximately the same size as an adult booklouse) and rounder than booklice. They also have a proportionally narrower head compared to the body.

Habitat and Biology

In outdoor environments, booklice are found on trees and shrubs, bird nests, and similar habitats where they feed on lichen, algae, fungi, and other organic detritus.

Indoors, they are found in humid, damp, generally dark areas where they feed on fungi and mold. They can be associated with starchy products such as paper, books, book bindings, and wallpaper, as well as flour and other stored grains. In these cases, the booklice are feeding on mold growing on those substrates.

Female booklice can produce about 60 eggs during the warm summer months, and their life cycle (from egg to adult) can be completed in less than one month. When temperatures are cooler, female booklice produce fewer eggs, and it can take over three months to complete their lifecycle.

Eggs are deposited singly and are often concealed with debris. Booklice undergo simple metamorphosis, so the immature nymphs look just like adults except that they are smaller. The species that commonly live in homes and other buildings usually have four nymphal stages.

Damage

Unlike silverfish, firebrats, and some other pests, booklice do not directly damage paper products, fabric, or other non-food items. Their feces can contaminate stored food products. Booklice do not bite, are not vectors of disease, and do not otherwise impact human or animal health.

Control

Because booklice are associated with humid and damp environments, the best control in most cases is to remedy the underlying water issue that is allowing them to reproduce and persist.

Lowering the relative humidity to less than 50% will prevent mold growth and booklouse development, so installing a dehumidifier, moisture absorber, or other method to lower the humidity in a room or specific area can be very effective.

If moisture is trapped in the wall void (e.g., in new construction that was not allowed to dry before drywall was installed), holes may need to be cut into the drywall to allow the wall void to dry out.

An air space under potted plants on windowsills will help keep the humidity down and reduce mold growth.

Other water issues, such as a leaky pipe or roof, should be remedied to reduce or remove damp conditions.

Stored food items that have booklice should be discarded as they are contaminated with mold and booklouse feces. Uncontaminated food should be kept dry and stored in tight-closing glass or plastic containers to prevent future mold growth.

Pesticides are not normally necessary to control booklice in homes, as remedying water issues is more effective.

Written December 1998 and revised January 2014 by Steve Jacobs. Revised July 2024 by Michael Skvarla.