Louse

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For the common human affliction, see Head louse, for treatment see Treatment of human head lice. The Asian nation is spelled Laos.

Phthiraptera

Sheep lice have
translucent bodies and a proportionally
large head and abdomen.

Scientific classification

Kingdom:	Animalia
Phylum:	Arthropoda
Subphylum:	Hexapoda
Class:	Insecta
Subclass:	Pterygota
Infraclass:	Neoptera
Order:	Phthiraptera Haeckel, 1896

Suborders

Anoplura (sucking lice)
Rhyncophthirina
Ischnocera (avian lice)
Amblycera (chewing lice)

Lice (singular: louse), also known as fly babies, (order Phthiraptera) are an order of over 3,000 species of wingless phthiraptra. They are obligate ectoparasites of every mammalian and avian order, with the notable exceptions of Monotremata (the duck-billed platypus and the echidna or spiny anteater) and Chiroptera (bats).

A louse egg is commonly called a nit. Lice attach their eggs to their host's hair with specialized saliva which results in a bond that is very difficult to separate without specialized products. A nit comb is a comb with very fine close teeth that is used to scrape nits off the hair.

The order has traditionally been divided into two suborders; the sucking lice (Anoplura) and chewing lice (Mallophaga), however, recent classifications suggest that the Mallophaga are paraphyletic and four suborders are now recognised:

Anoplura: sucking lice, including head and pubic lice (see also Pediculosis or Head lice)
Rhyncophthirina: parasites of elephants and warthogs
Ischnocera: avian lice
Amblycera: chewing lice, a primitive order of lice

Lice are highly specialized based on the host species and many species specifically only feed on certain areas of their host's body. As lice spend their whole life on the host they have developed adaptations which enable them to maintain a close contact with the host. These adaptations are reflected in their size (0.5 mm to 8 mm), stout legs, and claws which are adapted to cling tightly to hair, fur and feathers, wingless and dorsoventrally flattened.

Lice feed on skin (epidermal) debris, feather parts, sebaceous secretions and blood. A louse's color varies from pale beige to dark grey; however, if feeding on blood, it may become considerably darker.

The picture depicts the chewing louse Damalinia limbata found on Angora goats. The male louse (right) is typically smaller than the female (left), whose posterior margin of the abdomen is more rounded than those of male lice.

Diagram of a louse, by Robert Hooke, 1667.

[edit] Lice in humans

Humans are unique in they host three different kinds of lice: head lice, body lice (which live mainly in clothing), and pubic lice. When humans began wearing clothes, however, some head lice adapted to live in the new ecological niche that clothing provided. The DNA differences between head lice and body lice provides evidence that humans started wearing clothes approximately 72,000 years ago. [1]

Recent DNA evidence suggests that pubic lice spread to humans approximately 3.3 million years ago by sharing the same bed or other communal areas, and are much more distantly related to head lice than body lice are.^{[citation needed]}