The Psocoptera are a group of small soft, stout bodied insects which include Book Lice Liposcelis sp. which feed on the paste and bindings of old books as well as on the fungi which invades the pages, they will also feed on museum specimens if given the chance. There are around 2 000 in the world and 68 in Britain.
They are Hemimetabolous with thread like antennae of 12 to 50 segments, the compound eyes of many species look like hemisheres that have been stuck on the outside of the head, though in a few species of Liposcelidae they are greatly reduced. Some are winged, with delicate membraneous wings and some are not, the winged species possess 3 ocelli while the apterous (wingless) species have none. They have biting mouthparts, no cerci and date from the Permian times. Psocids have been recorded coming to light traps by some researchers.
Some species of Psocoptera have become accustomed to live in human buildings feeding on the variety organic matter to be found here, i.e. several species of Liposcelis. While others have taken a liking to our barns and other large stores of straw which supply them with both home and food, where they generally feed on either the detritus among the straw or the fungi which is feeding on the straw i.e. Pteradela pedicularia, and Ectobius briggsi. However the majority of Pscoptera are worthy of their common name of Bark Lice and live on and around trees. Here they feed on the Lichen and Micro-fungi which colonise the trunks of trees in most places where the air is not too polluted, i.e. Hyperetes guestfalicus and Trogium pulsatorium.
Some species live communally under a web they have spun under the bark of trees, others like various Graphopsocus species place only their eggs in a group under a silken web, they lay about 20 to 100 eggs and those which don't place them under a silken web may lay them either in groups or singly depending on species, further more some species are are vivaparous (giving birth to live young).
In different climates they can be uni/bi or even trivoltine (voltine refers to the number of generations per year hence univoltine means 1 generation per year etc.) They overwinter as eggs and the nymphs pass through 6 instars on their way to adult hood. Though many species are alate (i.e. have wings) they are notoriously reluctant to fly, the exception to this is Pteradela pedicularia which flies well and in large numbers on still days where it occurrs.
The taxonomy of Psocids involves 22 families divided between 3 Suborders, the Trogiomorpha with more than 20 antennal segments, the Troctomorpha with 11 to 17 antennal segments and the flagellum secondarily annulate (formed in ring-like segments, in this case there are more than one apparent annular segment per actual antennal segment), and the Psocomorpha with less than 13 antennal segments which are never secondarily annulate.