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Commonly called barklice or booklice, members of the order Psocoptera (psocids) are not true lice (order Phthiraptera) although they are closely related to parasitic lice. Unlike blood-sucking lice, psocids (pronounces so'-sid) are phytophagous, feeding on organic matter including algae, lichen, fungi, pollen, decaying plant particles (detritus), and occasionally dead animal matter. The habit of psocids includes living or dead foliage, ground litter, bark of trees, and inside human habitations. However, a few species of psocids are found living in mammal or bird nests, the fur of mammals, or the plumage of live birds. For example, members of the family Proquillidae reside in bird nests, where the feed on dead skin cells or feather residues, but do not damage the bird. According to N. C. State Entomology Department, members of this bird nest-dwelling family are believed to be the closest ancestors of true lice, which parasitize birds and mammals. Other than this interspecific behavior, phylogenetic similarities between parasitic lice and barklice are observed through similar mouth structures.

The mouthparts of psocids are arranged in a mortal-and-pestle design, allowing the insects to scrape food from organic matter and grind it up. This arrangement explains the origin of the name Psocoptera, derived from the Latin roots psokos ("rubbed or gnawed") and ptera ("winged"). Loosely translated, psocids are "winged insects that gnaw." Besides defining the order name, psocid mouthparts also place them on the evolutionary lineage. Out of the Hemipteroid evolutionary line (which includes orders Psocoptera, Phthiraptera, Hemiptera, and Thysanoptera), Psocoptera are generally considered the most primitive because their mouthparts are the least modified from the ancestral stock (N. C. State Entomology Department). Psocid-life fossils have been reported from the Permian and Jurassic periods (280-190 million years ago), but these fossils show a slightly more primitive wing venation than modern psocids. The earliest fossils that are essentially modern in form date from the Cretaceous period, known as the last portion of the "Age of the Dinosaurs" (146-65 million years ago). These psocid fossils are preserved in amber and found in Russia and central Canada ( Mockford, 1993).

Psocids are unofficially placed in two groups, barklice and booklice. Barklice are outdoor, winged forms living on tree trunks, branches, and leaves. Booklice are indoor, wingless forms that are sometimes found in old books. Booklice occasionally damage books by feeding on starchy materials in the binding. They will also feed on, and often destroy, collections of dried insect specimens. Other than these pests, psocids are rarely in contact with humans and are of little economic importance.

Psocids are active, fast running insects with stocky bodies. Their bodies and forewings are different shades of brown or grey. They have large heads with slightly bulging faces and huge compound eyes. Antennae contain 12-50 segments and sweep back towards the abdomen. The prothorax is small compared to the head. The external genitalia of both sexes are concealed.

Booklice are less than 2 mm long, wingless, and have no ocelli. Barklice have 3 ocelli and range from 5-10 mm long. Most barklice have 4 membranous wings that are held roof-like over the body at rest. Under certain environmental conditions, barklice wing form can change to brachyptery (short wings unsuitable for flight) or aptery (absence of wings) ( Gillot, 1995).


most advanced, have less than 13 antennal segments
  • Epipsocidae
  • Mesopsocidae
  • Myopsocidae
  • Polypsocidae
  • Pseudocaeciliidae
  • Psocidae - Common barklice
have 11-17 antennal segments
  • Liposcelidae - Booklice
  • Pachytroctidae
most primitive, have more than 20 antennal segments
  • Lepidopsocidae
  • Psyllipsocidae
  • Trigiidae - Granny booklice

Photo copyright Scott Camazine

Photo copyright Scott Camazine


Taxonomic Category Scientific Name Common Name
Phylum Arthropoda Arthropods
Class Insecta Insects
Order Psocoptera Psocids, Barklice, & Booklice

Synonyms: Corrodentia, Copeognatha, Psocina


barklice webbing
Photo copyright Wayne Brewer

Geographic distribution

WorldwideNorth America

Natural history
    Different families are associated with different habits. For example, Trogiidae and Liposceiidae live in human habitations while Psocidae, Myopsocidae, and Philotarsidae live on the bark of trees. Psocids have excellent powers of dispersal. They are often among the first insects to colonize disturbed areas.-- ( N.C. State Entomology Dept.)

    Maple and Boxelder are the most common plants that psocids inhabit. Most species are free living, but several species are gregarious, living under irregular, silken webs on tree trunks, branches, or roots of trees. These webs are spun from silk produced in the labial glands.


    Barklice are generally herbivores or detritivores, feeding on plants and debris. Several species are partial predators, eating eggs and scale insects. Many psocids eat fungi along with the leaf tissue that surrounds fungal hyphae. Booklice feed on starchy materials including cereals, bookbindings, stored grains, wallpaper paste, and fabric sizing.

    Predators of psocids include small sphecid wasps, daddy long legs, spiders, mites, and several types of small birds. Eggs are parasitized by mymarid wasps (Alaptus) and nymphs are paratized by braconid wasps (Euphoriella).--( Mockford, 1993)


    Psocids go through simple metamorphosis, with immatures resembling adults, except nymph wings are often small or absent. Reproduction in a few species of poscids is quite unusual. Several species of the genus Archipsocopis are viviparous, giving birth to live young. Males in some species are unknown, while in others parthenogenesis, or asexual reproduction, may occur.--( Gillot, 1995)

    Reproduction of psocids involves courtship preceding copulation. Receptive adults secrete a sex attractant pheremone to find mates. Males then perform a sideways gait in an effort to initiate copulation. The gait stimulates segments of the legs to rub together, producing a clicking noise. This gait is a courtship dance, with motions and sound.--( Mockford, 1993)

    During copulation, sperm is transferred via a solid or liquid spermatophore (a capsule formed in the male reproductive system that encloses sperm). Production of a solid spermatophore is associated with species that copulate rapidly while a liquid spermatophore is associated with slow reproduction.--( Mockford, 1993)

    Eggs are deposited singly or in cluster consisting of 20-100 eggs per brood. The eggs are either laid bare, covered with a silken web, or encrusted with material from the digestive tract. Psocid nymphs usually aggregate in groups, particularly in the North American species of Cerastipscous. These dense groups remain together until after they molt into adult forms.


    About 50 species of psocids are reported feeding on household and stored products. However, the majority of psocids are woodland insects having no contact with humans and thus are of little economic importance. The webbing of larvae can completely cover the bark of trees, but appear to cause no damage.-- ( Auburn Ag. Dept.) Since many psocids feed on mold, the presence of booklice is a good indication of high humidity. Thus, eliminating moist conditions effectively regulates control of pests.

Links to other sites

  • Mockford, Edward L. North American Psocoptera. Sandhill Crane Press. Gainesville Fl, 1993.
  • Gillot, Cedric. Entomology, 2nd Ed. Plenum Press. New York, 1995.

Blythe Layng, Biology Major, University of Georgia, Athens

Thanks to Sabina Gupta, Denise Lim, and Dr. John Pickering for technical and web support in developing this page.

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