BUG OF THE MONTH: January 1995


Order Psocoptera, family Liposcelidae

Copyright © 1995 by  Louise Kulzer

This article originally appeared in Scarabogram, Jan. 1995, New Series No. 177, pp. 2-3.

drawing of booklouse
Liposcelis, length 1-1.5 mm

In these dark & dreary winter months when many of the flashier insects make themselves scarce, the gentle booklice remain faithful companions. "Booklice" is a poor name for the psocids, for they are not parasitic and indeed are not lice at all, a name more properly reserved for the Mallophaga and Anoplura (biting and sucking lice). Psocids are differentiated by habitat a bit like the country mouse and the city mouse. They either live outside, inhabiting bark, litter, lichen and other situations rich in organic matter, or else they live indoors. Outdoor psocids typically have 2 pair of wings held rooflike over the body. Indoor psocids are usually wingless. It is the indoor variety of psocid that is typically given the name "booklouse." [A good general reference is Mockford (1993).]

Booklice are small, rather simple insects with soft bodies, chewing mouthparts, and relatively long antennae. The head is slightly inflated, giving it a bit of a bulging appearance. I think it makes them look intellectual, somewhat like the stereotypic "brainy" person. The commonest household species is Liposcelis decolor, formerly called L. divinatorius, which reproduces parthenogenically (females lay eggs without mating).

They feed mainly on microscopic molds and mildews. Since the bindings and sizing used in books are susceptible to mildew, psocids find them of interest (and you thought they were literary critics!) Any book that smells "musty" is fair game for booklice. They also are interested in cereal products, straw, and the domestic fallout collecting in window sills and crevices. Indeed, booklice may actually prove to be much better companions that I initially thought, for they are reported to live not only in cracks & crevices of houses, but also in furniture, rugs, cupboards, and closets. However, don't be alarmed. Psocids rarely do much damage. If they do get too abundant, they can be easily controlled by taking away sources of dampness upon which their mildew food supply depends.

According to Mallis (1990), "Although psocids may become...annoying by crawling over everything in the house... they usually cause negligible damage to commodities." They have caused "heavy losses to property owners resulting not from destruction of buildings and furnishings but from broken leases, lawsuits to recover damages for fancied loss to health and furnishings, and payment...of pest control operators."

Next time you curl up to re-read that great mystery book, check it out. Psocids may add a new dimension of enjoyment.


Mallis, Arnold, et al. 1990. Handbook of Pest Control. Seventh Edition. Franzak & Foster Co., Cleveland, Ohio, 1152 pp.

Mockford, Edward. 1993. North American Psocoptera. Flora & Fauna Handbook No. 10, 455 pp.

This page last updated 16 June, 2005