Common Name: Booklice, barklice, psocids
Scientific Name: Liposcelis species (Family Liposcelidae) are most common for indoors
Psocids, insects of the Order Psocoptera, 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. Booklice are found worldwide and throughout the United States, with about 287 species known from the United States.
Adult booklice are 1/32 to 1/8 inch long, soft bodied and look like tiny termite workers except that the antennae are long and threadlike. The prothorax (front portion of the thorax) is reduced and neck-like. Wings, if present, are 4 in number and membraneous (like cellophane). The front wings are larger than the hind wings and the wings are held roof-like over body at rest. Booklice have chewing mouthparts. Nymphs are similar to adults in appearance but lack wings, although wing pads may be present.
(1) Chewing lice (order Mallophaga) are ectoparasites of birds and mammals. Sucking lice (order Anoplura) are ectoparasites of mammals. Both groups of lice have short antennae and are wingless. (2) Termite nymphs and workers (order Isoptera) have short antennae and are associated with granular mudlike shelter tubes in infested wood and cardboard.
Most species are represented by both males and females while some are parthenogenetic (reproduction without males). Most species which occur outdoors are fully winged whereas, those which are found indoors are typically wingless or with reduced wings.
The typical booklouse life cycle involves an adult period of sexual inactivity, courtship and copulation, oviposition (7 to 44 eggs are laid per female), egg hatch and 4 to 6 nymphal instars (growth stages between molts). Nymphs resemble adults in form except for wings. The 4 booklice / psocids most commonly encountered in homes and/or granaries are the banded psocid (Liposcelis bostrychophila), cereal psocid (Liposcelis decolor), grain psocid (Liposcelis entomophila) and larger pale trogiid (Trogium pulsatorium). Developmental period (egg to adult) requires about 1 month and the life cycle (egg to egg) requires 111 to 130 days. Adults can live over 3 months.
Booklice/psocids are typically found in areas of high relative humidity. High humidity conditions are also required for the growth of mold, the primary food of most psocids. When the humidity drops below a psocid's comfort level, they migrate, sometime 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 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 to 4 weeks with the onset of warm weather.
In older homes, booklice are most commonly found in association with damp books; the starch sizing and glues used in books readily support mold growth. Booklice 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 plant / cellulose material as stuffing, in rope and twine made from flax, hemp, or jute fibers and in closets, pianos, and cabinets.
In new homes, apartments, and office buildings, booklice are sometimes found within 4 to 12 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.
In warehouses, groceries and granaries/grain elevators, booklice are commonly found associated with damp spillage. In food plants and many warehouse situations, they are commonly associated with improperly stored wooden pallets which have gotten damp and become infested with mold. Outdoors, booklice/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. The 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.
Cultural Control And Preventative Measures
Booklice/psocid control is achieved by controlling the humidity. Lowering and keeping the relative humidity below 50% eventually kills booklice. Quicker drying accelerates elimination.
High relative humidity conditions in new and damp homes should be corrected via the use of dehumidifiers, ventilation enhancement, air conditioning and plumbing repairs indoors. Structural repairs and landscaping/irrigation modifications should be performed outdoors.
In 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.
A Rottler technician will inject insecticide aerosol and dust formulations into structural voids where booklice are breeding in damp, moldy situations. A residual insecticide will be applied as an exterior perimeter (barrier) treatment around the foundation as well.