General Information

Sometimes called booklice when found indoors and barklice when found outside, psocids are soft-bodied insects that may or may not have wings, depending on the habitat in which they are found. Commonly found outside on tree bark, in foliage, or under rocks, the insects become more noticeable when large groups are found together. Inside the house, psocids may be found in books, book bindings or on other materials made of paper, and any surface of mold/fungal growth. The insect becomes a pest once found in homes or businesses and poses no risk to outdoor flora.

Appearance & Identification

What do psocids look like?
Usually less than 1/16 of an inch long, booklice are typically wingless and possess a flattened body with a large head and abdomen and a tapered thorax. With segmented antennae that are long and threadlike, chewing mouthparts, and large, protruding eyes on the sides of the head, psocids are typically white, gray, or brown in color. Under a microscope, the insect has a large nose-like feature called a clypeus. Barklice possess wings but are not very good fliers. When at rest, the wings generally sit above the insect, almost like a roof structure. Some barklice may reach up to 1/4 of an inch in length.


Part of the insect order Psocoptera, psocids appear as tiny tan specks on the bark of both coniferous and deciduous trees. Adults feed primarily on the lichens and fungi that grow on the bark, not the tree itself. When indoors, the insect may find a home inside furniture, on window sills, near potted plants, under wallpaper, and inside books. If psocids are found in food stores, it usually means that the storage area has become damp and humid, leading to the growth of fungi or mold that acts as a source of food for the insects. When found in large groups among grains and other foodstuffs, the presence of psocids renders most food unfit to eat due to the additional presence of unsafe molds.


What do psocids eat?
Though resembling lice in both size and shape, psocids do not feed on blood. Booklice commonly feed on fungi, grains, starchy materials, molds, and even insect fragments. Indoor psocids also feed on the glue in book bindings and damp cardboard. When found in the home, booklice may also feed on microscopic organisms, molds, and fungi growing in cereals and grains. Barklice feed on lichens, pollen, decaying plant material, fungi, and a host of other organic material.


During summer months, females may produce up to 60 eggs. The entire life cycle may only take one month, from egg to adult. The typical life cycle starts with an egg, includes four nymphal stages, and concludes when immature psocids become adults. The eggs look about a third of the size of adults, appear translucent, and may be glued to the surface where laid. Eggs may be laid singly or in groups and then are typically covered with available debris or thread-like substances to conceal and protect the offspring. Nymphs look like smaller versions of adults but are sexually immature until reaching adulthood. In ideal temperatures, psocids may live up to three months. Most adults are thought to be female and therefore reproduce asexually.

Problems Caused by Psocids

The insect acts more as an annoyance than an actual pest. Feeding habits outside do no significant damage to plants and other vegetation. Indoors, the presence of psocids means that some of the cereals and grains in the home have taken on moisture and are now growing mold (or perhaps there was a moisture leak behind a wall or in a ceiling). Booklice feeding on these molds and fungi may prove that certain foodstuffs have become unfit to consume, decrease the size of grains, and, in rare instances, trigger allergies in people. When eating starchy materials, wallpaper glue, and book bindings, the insects become a definite nuisance, especially in large numbers. Though often confused with true lice, psocids do not bite and therefore do not transmit diseases to humans or pets.

Signs of Infestation

The most obvious sign of infestation remains the noticeable damage interior psocids cause to certain foodstuffs, paper products, cardboard, or moisture-laden areas of the home or business. Visibly seeing large numbers of the small insects is a definite indicator of a psocid infestation. Home and business owners should frequently check areas of moisture for signs of molds and other food sources that may entice psocids to stay and establish breeding sites.


The best way to prevent a psocid infestation is to lower humidity levels in the home or business. Store all dry foods in tightly sealed containers and adjust and correct moisture levels and high humidity, if possible. In rare cases when a large amount of booklice remain in the home, books as well as bindings and even wallpaper paste may become susceptible. In the instance of a large and severe infestation, contacting a trained and licensed pest control agent may prove beneficial in finding a permanent solution.