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Psocids in homes

Jeffrey Hahn and Stephen Kells

Psocids (pronounced SO-sids) are common outdoor insects, although some species are occasionally are found indoors. These are also known as barklice and booklice.


Photo: Dave Shetlar, Ohio State University

Typical booklice. Note the conspicuous nose (clypeus).


Psocids are soft bodied insects, less than 3/16 inches long with long, slender antennae. They are generally white, gray or brown in color and may either have four wings or are wingless. Under magnification, you can see the presence of a large, conspicuous nose (called a clypeus).


Most psocids live outdoors and have wings. They can be found on tree bark, tree and shrub foliage, or under stones. These psocids are known as barklice. They sometimes can become quite conspicuous when they congregate in large groups. Barklice feed on fungi, lichen, pollen, decaying plants, and other organic material. They are harmless to plants and no control is necessary.

There are a few species of wingless psocids that may be seen commonly in buildings, usually Liposcelis spp. These psocids are commonly called booklice because of their association with books or paper. Booklice feed most commonly on molds as well as fungi, grains, insect fragments, and other starchy material, including glue from book bindings.

In homes, they can be found in damp, warm, undisturbed places where mold and fungi are growing. They are more likely to be a problem during summer. They may also be a problem in situations where stored cardboard becomes wet. Psocids may become a problem in commercial food storage and food manufacturing facilities.


Booklice are rarely damaging inside homes but they can become a nuisance because of their presence, especially when they occur in large numbers. Despite being referred to as ‘lice’, neither booklice nor barklice are harmful to people or pets. In food storage, their presence may also indicate bacterial or mold growth.


The most effective method for controlling booklice is to reduce moisture. Psocids generally do not survive when humidity falls below 50%. A dehumidifier or fan is effective in reducing moisture. Sometimes airing out a room to keep the air moving may be sufficient. Store boxes, bags, books, and papers off of the floor to minimize exposure to dampness.

Correct any moisture problems that may occur. This can include:

Insecticides are usually not necessary. Keep in mind that insecticides are not effective by themselves if moisture is still a problem. The products that are typically available to residents are generally not effective against psocids.

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