Order Psocoptera - Psocids or Booklice

• Booklouse or Dust Louse
• Barklouse
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Small, soft-bodied insects with two pairs of membranous wings or wingless. When at rest, most winged species hold their wings steeply roof-wise over the body. Head quite broad, with long filamentous antennae and biting mouthparts. Eyes often large and protruding from the sides of the head. Legs with two or three tarsal segments. Cerci absent. Metamorphosis simple, usually with six nymphal stages before reaching maturity, although some wingless forms may have fewer stages. This is a relatively small Order with about 2,000 described species. Over 90 species have been recorded from Britain, but only about 50 of these are known to occur naturally. The others are mostly casual imports, often in stored products, and some are recorded only from single specimens found in warehouses or ships holds.

The best known Psocids are the very small, wingless species commonly known as Booklice or Dustlice, which often infest houses, libraries, food stores, warehouses and other buildings. However, the majority of species, often called Barklice, live outside on tree bark, leaves, fences, stone walls and in old birds' nests. Most of these outdoor species are fully winged.

Description. Small wingless species, up to 2 mm long. Pale yellowish-white or brown in colour. 'Thigh' segments (femora) of hind legs very broad.

Biology. Mainly found indoors (at least in temperate regions), living on all kinds of starchy organic matter such as stored food and paper. Often found among undisturbed books and under peeling wallpaper, feeding on glue, paste and minute traces of mould. Flour, meal and other cereal products are also eaten. Breed continuously throughout the year indoors.

Distribution. Cosmopolitan, in warehouses and other buildings. Often transported in the cargo holds of ships.

Photo (right): Perry Babin, CCA Share Alike License

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Description. Adults usually winged, up to 10 mm long, with thorax typically 'humped' in side view (see photograph). Generally pale to dark brown in colour. Some with patterned wings, like the species (Graphopsocus cruciatus) in the photograph.

Biology. Found outdoors on various trees and bushes, mainly feeding on algae and minute fungi growing on bark and leaves. Often several generations in a year.

Distribution. The species shown in the photograph occurs in most parts of central and northern Europe, including the British Isles.

Photo (right): Jean-Jacques Milan, GNU Free Documentation License