Often overlooked, these are also known as booklice (species found predominately indoors) or more recently barkflies. They are quite small insects ranging from 1.5-7 mm long, and can be confused with psyllids, jumping plant lice, which do what the names says and jumps when disturbed, where as barklice don’t jump. The reference to ‘lice’ is a bit of a misnomer as they are not parasitic but free-living insects.
Psocoptera are regarded as the most primitive amongst insects, as their mouth parts show little modification from those of the earliest known fossils.
Barklice feed on various ‘microflora (algae such as Pleurococcus, lichens and fungi) or on more general organic matter which often occurs on surfaces of bark or the foliage of trees. Not all barklice are associated with trees, as some are found in low vegetation, leaf litter and under stones. Some species are fully winged, and some are only partially winged or wingless.
There are around 4,400 psocid species worldwide, 1,000 in Europe, and 100 in Britain, and many go unoticed and unrecorded, although most every tree is likey a home to them.
68 of these species come under the barklice or barkflies umbrella which are found outdoors, and the remaining booklice are found indoors. These are wingless and grow up to around 2 mm long. These are most commonly found in human dwellings and warehouses where they feed on stored grain, book bindings, wallpaper paste and other starchy products, and on the minute traces of mould found in old books. They can sometimes cause damage to stored museum collections of insects and plants. A few Psocoptera live in bird nests feeding on feathers and dead skin cells.
Family Caeciliusidae (Lizard barklice)
Family Ectopsocidae (Outer barklice)