are often called booklice or barklice because of their superficial
resemblance to some lice species, and because they are often
found on moldy books and papers in damp situations indoors,
and under loose, damp bark outdoors. They are primarily nuisance
pests in homes but are of considerable importance in insect
collections, stored products, and food processing facilities.
Their dead bodies in house dust are thought to contribute
to asthma attacks. Psocids are found worldwide and throughout
the United States, with about 287 species known from the United
about 1/32-1/4" (1-6 mm) long; soft bodied, look like
tiny termite workers. Head somewhat bulging, eyes varying
from large and globose to a single ommaticlium/facet, ocelli
present or absent. Antennae long, threadlike, 11-50-segmented.
Prothorax reduced, necklike. Wings if present, 4 in number,
membraneous (like cellophane), front wing larger than hind
wing and often with pigmented spot/cell (pterostigma) along
front edge before apex of vein R1, number of veins reduced
and few crossveins; wings held rooflike over body at rest;
wings showing various states of reduction to being absent.
Tarsi 2- or 3-segmented. Cerci absent. Mouthparts chewing.
similar to adults in appearance but lack wings, although wing
pads may be present.
(1) Chewing lice (order Mallophaga) with tarsi 1- or 2-segmented,
antennae short, 3- to 5-segmented, and ectoparasites of birds
and mammals. (2) Sucking lice (order Anoplura) with tarsi
1 -segmented, antennae short 3- to 5-segmented, and ectoparasites
of mammals. (3) Termite nymphs and workers (order lsoptera)
with antennae short, usually beadlike, tarsi 4-segmented,
and cerci present.
Cosmopolitan grain psocid, Lachesilla pedicularia (Linnaeus);
Lachesilliclae. Adults with head and thorax medium brown,
abdomen pale brown with reddish brown ring incomplete ventrally;
front wing clear except CU1a, M1, and M2 narrowly brown bordered,
with pterostigma narrower at base, M 3-branched; antenna 13-segmented;
length from head to closed wing tips about 1/16-1/8"
(2-4 mm); tarsi 2- or 3-segmented; found primarily outdoors,
common in houses, occasionally in stored grain; distributed
worldwide, occurs throughout the United States.
Banded psocid, Liposcelis bostrychophila Badonnel; Liposcelididae.
Adults (known only from females) pale to medium brown with
yellowish tinge, head and thorax darker than abdomen; wingless;
antenna 15-segmented (rarely fewer), with at least some segments
annulated (ringed); compound eye with 7 ommatidia (facets);
hind femur with a lateral protuberance, tarsi usually 3-segmented;
found outdoors, litter of chick coups, common in old books
in damp places and in stored grain; distributed worldwide,
occurs throughout but scattered in the United States east
of Rocky Mountains, and in western Canada.
Cereal psocid, Liposcelus decolor (Pearman) (=Liposcelus divinatorius
(Muller), =Liposecelus terricolis (Badonnel)); Liposcelididae.
Adults grayish white to medium brown with scattered darker
spots on top of head and sides of thorax; female wingless;
antenna 15segmented (rarely fewer), with at least some segments
annulated (ringed); female compound eye with 7 ommatidia (facets);
hind femur with a lateral protuberance, tarsi usually 3-segmented;
found outdoors, in houses and warehouses, in stored grain
and agricultural products; probably distributed worldwide,
occurs throughout the United States except for the southeastern
Grain psocid, Liposcelis entomophila (Enderlein) (formerly
Liposcelis entomophilus); Liposcelididae. Adults creamy yellow
with abdominal segments marked with pale bands of purplish
brown which may fade out along midline; female wingless; antenna
15-segmented (rarely fewer), with at least some segments annulated
(ringed); female compound eye with 8 ommatidia (facets); hind
femur with a lateral protuberance, tarsi usually 3-segmented;
found primarily in domestic situations, common in stored grain
and collections of biological specimens/material; distributed
worldwide, occurs in midwestern and southeastern United States.
Larger pale trogiid or deathwatch psocid, Trogium pulsatorium
(Linnaeus); Trogiidae. Adults creamy yellow with reddish brown
band through middle of head and another from compound eye
to antennal base, abdomen with reddish brown spots mostly
along front margin of segments; antenna with at least 21 segments;
front wings represented as flat scales which reach base of
abdomen; tarsi 3-segmented; found almost exclusively in homes,
granaries, and mills; widespread in Europe and Japan southward
to Australia, occurs primarily in the northeastern United
Most species are represented by both males and females while
some are parthenogenetic (reproduction without males) in part
or all of their geographic range. Most species which occur
outdoors are fully winged whereas, those which are found indoors
are typically wingless or with reduced wings.
typical psocid life cycle involves an adult period of sexual
inactivity, courtship and copulation (several times in males,
often only once in females), oviposition, egg hatch, and 46
are laid either bare or encrusted, and with or without webbing
over them. Nymphs resemble adults in form except for wings
but lack functional ocelli, never have more than 2-segmented
tarsi, and early instars have fewer antennal segments than
adults. Nymphs of adults with extreme wing reduction tend
to have 4 nymphal instars whereas, those of fully-winged adults
tend to have 6 instars.Probably the 3 psocids most commonly
encountered in homes are the banded psocid, cereal psocid,
and larger pale trogiid. Since more is known biologically
about the cereal psocid, it is summarized here. At 80 degrees
F (27 degrees C) and 65% RH, preoviposition lasts 2- weeks,
eggs are laid 1 every 12 hours until about 75% of total are
laid and then only occasionally, 3 larval molts occur, and
adults live over 3 months; developmental period (egg to adult)
requires about 1 month. In southern Louisiana, from October
to January, at 50-87-F (10-30 degrees C), preoviposition lasts
31-54 days (average 45 days), 7-44 eggs are laid (average
of 20 eggs), eggs require 11-27 days (average 21 days) to
hatch, the life cycle (egg to egg) ranges from 111-130 days,
and the postoviposition period lasts 1-24 days (average 9
days). However from June to August at 60-95 degrees F (16-35
degrees C), eggs average 6.9 days to hatch, an average of
57 eggs are laid, and the average life cycle (egg to egg)
is 24.4 days. Average time to egg hatch is 21 days, 24-65
days are required to reach sexual maturity, and 24-110 days
are required for the life cycle (egg to egg). They can overwinter
in the egg or nymphal stage. This species is primarily parthenogenetic
although males are known.
each species, there is a critical relative humidity below
which they lose water to the environment and eventually die
from desiccation. For many species this critical range varies
from 50-60% RH. Dehydrated specimens become lethargic and
have flattened and contracted abdomens. When returned to a
RH above their critical point, they readily absorb moisture
and become turgid, sometimes in as little as 2-3 hours.
are typically found in areas of high relative humidity because
they have trouble controlling water loss through their exoskeletons.
High humidity conditions are also required for the growth
of mold, the primary food of most psocids. When the humidity
drops below a psocid species critical level, they migrate,
sometimes in great numbers, to areas of higher RH or eventually
die. Another reason their population may seem to go from zero
to thousands in a few weeks is that because of their small
size they are rarely noticed when their numbers are low. Also,
adults usually die off in the winter but the eggs and/or small
nymphs can survive the cold temperatures and can become adults
in 3-4 weeks with the onset of warm weather.
older homes, psocids are most commonly found in association
with damp books whose starch sizing and glues readily support
mold growth. Psocids are also found in other damp areas with
mold growth such as bath traps with leaking or sweating pipes,
in wall, floor, and window and door casing voids, storage
trunks, groceries, stored products such as flour, rugs, paper,
straw matting, cardboard cartons, upholstered furniture containing
Spanish moss as stuffing, in tow (flax, hemp, or jute fibers),
and in closets, pianos, and cabinets.
new homes, apartments, and office buildings, psocids are sometimes
found within 412 months after construction before the plaster
or sheetrock walls have dried out. This dampness associated
with plastering temporarily supports mold growth, especially
in wall voids.
warehouses, groceries, and granaries/grain elevators, psocids
are commonly found associated with damp spillage. In food,
glass, pharmaceutical, bottling, canning, etc. production
plants and many warehouse situations, they are commonly associated
with improperly stored wooden pallets which have gotten damp
and become infested with mold.
situations where psocids have been found include herbaria
(plant collections), insect collections, libraries, and insect
light trap (ILT) catch trays which have not been emptied on
a timely basis. The senior author was involved with an infestation
in a newly erected partition wall of a major art museum where
plexiglass was used instead of sheetrock and the voids were
filled with peanut hulls as decorative material.
psocids occur in bird and mammal nests, living foliage, dead
foliage, ground litter, on top of tree bark, underneath loose
tree bark, and on rock surfaces. They have also been found
in mammal fur.
larger pale trogiid or deathwatch psocid gets the later common
name from the tapping sounds it produces by striking its abdomen
against paper and similar materials. Other species may also
produce such sounds.
cereal psocid and larger pale trogiid are recorded as predators
of the eggs of the Angoumois grain moth, Sitotroga cerealella
(Olivier), and the banded psocid feeds on the eggs of the
Indianmeal moth, Plodia interpunctella (Hubner).
control is achieved by controlling the humidity. Lowering
and keeping the humidity below 50% eventually kills psocids;
a greater and/or quicker reduction of humidity reduces the
time required. Exposed psocids can readily be killed with
a directed ULV application of appropriately labeled material,
but keep in mind that most of the psocid population will not
be in an exposed posture.
extreme or sensitive situations, fumigation may be required
or justified. The senior author was involved with a square
block sized glass container production plant and a beverage
filling plant which required fumigation. Both resulted from
improper pallet storage, and immediate elimination was demanded
because of the threat of contract cancellation by their customers.