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          Psocoptera.-- Pearman (1932) noted that several psocid species were predaceous on Coccidae, particularly mealybugs.  They feed also on various insect eggs and possibly on small aphids.  However, other researchers believed that their food consists mostly of the wax secretions of the scale insects rather than the body contents.  They are small soft-bodied insects, most being <6 mm long.  Three are ca. 72 genera and 340 species known in the United States and Canada.  They have been referred to as "bark lice," but are known to frequent an array of habitats.


          Eggs are laid singly or in clusters, sometimes covered with silk or debris.  Most species have 6 nymphal instars.


          These insects that are commonly known as booklice, barklice or barkflies. They date from the Permian period, 294–249 million years ago. They are often considered to be the most primitive of the Hemiptera-type insects. Their name originates from the Greek word psokos which means gnawed or rubbed and ptera meaning wings. There are more than 5,511 species in 41 or 42 families in three suborders. Many of these species have only been recently described.  They  range in size from 1.1-10.2 millimeters in length.


          The species known as booklice derive their common name from being usually found around old books and they feed upon the paste in the binding. Barklice are harmless and found on trees, where they feed on algae and lichens. None are currently considered endangered.  Rather they appear to be extending their range as in 2007, Atlantopsocus adustus, native to Madeira and the Canary Islands, was found in southwestern England.


          All are scavenging insects with a a generalized body shape. They feed mainly on fungi, algae, lichen, and organic detritus. They have chewing mandibles, and the central lobe of the maxilla is modified into a thin rod, which is used to support the insect while it scrapes up detritus with its mandibles. They also have a swollen forehead, large compound eyes, and three ocelli. Some species are able to spin silk from glands located in their mouth.

The forewings range to 1.6 times as long as the hindwings, and all four wings have a simple venation pattern, with few cross-veins. The legs are thin and suited for walking, rather than gripping, as is found in the true lice. The abdomen has 9 segments, and no cerci are present.


          There is often much variation in the appearance of individuals within the same species. Many have no wings or ocelli, and may have a distinct shape to their thorax. Other, variations are also known, such as changes to the development of the setae. The purpose of such changes is uncertain, but their function appears to be different from similar variations found in the Homoptera . However, many species are parthenogenic, and the presence of males may vary between different races of the same species.


          The eggs are laid in tiny crevices or on foliage, although a few species are known to be viviparous. The young  or nymphs emerge as miniature, wingless versions of the adult. These usually molt six times before reaching the adult stage. The total lifespan is short and hardly ever more than a few months.


References:   Please refer to  <biology.ref.htm>, [Additional references may be found at:  MELVYL Library]


García, A. N. Aldrete. 2006. "New genera of Psocoptera (Insecta), from Mexico, Belize and Ecuador (Psoquillidae, Ptiloneuridae, Lachesillidae)". Zootaxa 1319: 1–14.


Hoell, H.V., Doyen, J.T. & Purcell, A.H. 1998. Introduction to Insect Biology and Diversity, 2nd ed.. Oxford University Press. pp. 404–406.


Lienhard, C. & C. N. Smithers. 2002. "Psocoptera (Insecta): World Catalogue and Bibliography". Instrumenta Biodiversitatis (Muséum d'histoire naturelle, Geneva) 5. 


Meyer, J. R.  2005.  Psocoptera". North Carolina State University


O'Toole, C.  2002. Firefly Encyclopedia of Insects and Spiders. Toronto: