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Louse (plural: lice) is the common name for members of the order Phthiraptera, which contains nearly 5,000 species of wingless insect. Lice are obligate parasites, living externally on warm-blooded hosts which include every species of bird and mammal, except for monotremes, pangolins, bats and cetaceans. Lice are vectors of diseases such as typhus. Chewing lice live among the hairs or feathers of their host and feed on skin and debris, while sucking lice pierce the host's skin and feed on blood and other secretions. They usually spend their whole life on a single host, cementing their eggs, which are known as nits, to hairs or feathers. The eggs hatch into nymphs, which moult three times before becoming fully grown, a process that takes about four weeks. Humans host three species of louse, the head louse, the body louse and the pubic louse. The body louse has the smallest genome of any known insect; it has been used as a model organism and has been the subject of much research. Lice were ubiquitous in human society until at least the Middle Ages. They appear in folktales, songs such as ''The Kilkenny Louse House'', and novels such as James Joyce's ''Finnegans Wake''. They commonly feature in the psychiatric disorder delusional parasitosis. A louse was one of the early subjects of microscopy, appearing in Robert Hooke's 1667 book, ''Micrographia''. ==Classification== The order Phthiraptera is clearly a monophyletic grouping, united as the members are by a number of derived features including their parasitism on warm-blooded vertebrates and the combination of their metathoracic ganglia with their abdominal ganglia to form a single ventral nerve junction. The order has traditionally been divided into two suborders, the sucking lice (Anoplura) and the chewing (Mallophaga); however, recent classifications suggest that the Mallophaga are paraphyletic and four suborders are now recognized: * Anoplura: sucking lice, occurring on mammals exclusively * Rhynchophthirina: parasites of elephants and warthogs * Ischnocera: mostly avian chewing lice, however, one family parasitizes mammals * Amblycera: a primitive suborder of chewing lice, widespread on birds, however, also live on South-American and Australian mammals Nearly 5,000 species of louse have been identified, about 4,000 being parasitic on birds and 800 on mammals. Lice are present on every continent in all the habitats that their host animals and birds occupy.〔 They are found even in the Antarctic, where penguins carry 15 species of lice (in the genera ''Austrogonoides'' and ''Nesiotinus''). File:Ricinus bombycillae (Denny, 1842).JPG|''Ricinus bombycillae'', an Amblyceran louse from the bohemian waxwing File:Trinoton anserinum (Fabricius, 1805).JPG|''Trinoton anserinum'', an Amblyceran louse from a mute swan File:Lice image01.jpg|''Damalinia limbata'' is an Ischnoceran louse from goats. The species is sexually dimorphic, with the male smaller than the female. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Louse」の詳細全文を読む スポンサード リンク
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