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).
Suborder EUPSOCIDA (PSOCOMORPHA):
most advanced, have less than 13 antennal segments
- Psocidae - Common barklice
have 11-17 antennal segments
- Liposcelidae - Booklice
most primitive, have more than 20 antennal segments
- Trigiidae - Granny booklice
Photo copyright Scott Camazine
Photo copyright Scott Camazine
Synonyms: Corrodentia, Copeognatha, Psocina
||Psocids, Barklice, & Booklice
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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