The Bugwood Network

Order Psocoptera:
Psocids, barklice and booklice

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G. Keith Douce, Associate Professor of Entomology, The University of Georgia

Description: Psocids are small soft-bodied insects, most of which are less than 1/4 inch (<6mm) in length.  Wings may or may not be present, and both long-winged and short-winged individuals occur in some species.  The winged forms have four membranous wings:  the front wings are a little larger than the hind wings, and they are usually held roof-like over the abdomen when at rest.  The antennae are generally fairly long.  Psocids have chewing mouthparts and simple metamorphosis. 

The term "lice" in the name is somewhat misleading, for none of these insects are parasitic and relatively few are louselike in appearance.  The eggs of psocids are laid singly or in clusters and are sometimes covered by silk or debris.  Most species pass through six nymphal instars. 

Evidence:  Some 40 genera and nearly 150 species of psocids are known from the U.S., but most people see only a few species that occur in houses or buildings.  Most of the species found in buildings are wingless, and because they live among books or papers, are usually called booklice.

The majority of psocids are outdoor species with well-developed wings, and occur on the bark or foliage of trees and shrubs or under stones or bark, and are referred to as barklice.  The barklice frequently live in very large clusters, and characteristically, when disturbed, the whole mass appears to move at once.

Damage:  The psocids feed on molds, fungi, cereals, pollen, fragments of dead insects, and similar materials.  The species occurring in buildings sometimes build up large numbers that have been thought to cause damage by feeding on the starches in book bindings.  Generally, psocids rarely cause significant damage, but can become a nuisance when populations become large.

Some species are of barklice are gregarious, living under thin silken webs: one southern species often makes unsightly webs on tree trunks and branches.  The barklice are only known to feed on decaying organic matter, and consequently, are a curiosity and present no real problem other than being a general nuisance.  Contact your local county extension office for more information.


Borror, D. J, and D. M. DeLong.  1971.  An Introduction To The Study Of Insects.  Holt, Rinehart and Winston, NY, NY . 812 p.

Coulson, R. N. and J. A. Witter.  1984.  Forest Entomology: Ecology and Management.  John  Wiley & Sons, Inc. 669p.

Day, E. 1996.  Psocids.  Virginia Coop. Ext. Serv. Entomology Department Factsheet.

Lyon, W. F.  Booklice.  HYG-2080-93.  Ohio State Univ. Ext. Factsheet - Entomology. Ohio   State Univ. Columbus,  OH.

Photo Credits:

Image 1   Forest Insects and Their Damage Photo CD vol. 1 no. 48.  Andrew Boone, South
               Carolina Forestry Commission


The Bugwood Network and Forestry Images Image Archive and Database Systems
The University of Georgia - Warnell School of Forestry and Natural Resources and College of Agricultural and Environmental Sciences - Dept. of Entomology

Last updated December 2018

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