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Lice (singular: louse), also known as fly babies, is the common name for over 3000 species of wingless insects of the order Phthiraptera; three of which are classified as human disease agents. They are obligate ectoparasites of every avian and mammalian order except for Monotremes (the platypus and echidnas), bats, whales, dolphins, porpoises and pangolins.

Description

As lice spend their entire lives on the host, they have developed adaptations which enable them to maintain close contact with the host. These adaptations include their size , their stout legs, and their claws which allow them to cling tightly to hair, fur and feathers; other adaptations include being wingless and dorsoventrally flattened. Lice do not like oils. One of the best ways to get rid of lice is by bathing the head in olive oil.Lice have no ocelli and only small compound eyes; many species have no eyes at all. Other distinguishing features include short antenna, the absence of abdominal cerci, and the thoracic segments being at least partially fused. Most lice have relatively simply chewing mouthparts, but in some they are highly adapted for piercing and sucking.

Lice cannot jump or fly.

Biology

Most lice are scavengers, feeding on skin and other debris found on the host's body, but some species feed on sebaceous secretions and blood. Most are found only on specific types of animal, and, in some cases, only to a particular part of the body; some animals are known to host up to fifteen different species, although one to three is typical for mammals, and two to six for birds. For example, in humans, different species of louse inhabit the scalp and pubic hair. Lice generally cannot survive for long if removed from their host.

A louse's color varies from pale beige to dark gray; however, if feeding on blood, it may become considerably darker. Female lice are usually more common than the males, and some species are even known to be parthenogenetic. A louse's egg is commonly called a nit. Many lice attach their eggs to their host's hair with specialized saliva; the saliva/hair bond is very difficult to sever without specialized products. Lice inhabiting birds, however, may simply leave their eggs in parts of the body inaccessible to preening, such as the interior of feather shafts. Living lice eggs tend to be pale white. Dead lice eggs are more yellow.

Lice are exopterygote, being born as miniature versions of the adult, known as nymph. The young moult three times before reaching the final adult form, which they usually reach within a month of hatching.

Classification

World War II-era American poster, created to prevent the transmission of lice between servicemen.
The order has traditionally been divided into two suborders, the sucking lice (Anoplura) and the chewing lice (Mallophaga); however, recent classifications suggest that the Mallophaga are paraphyletic and four suborders are now recognised:

It has been suggested that the order is contained by the Troctomorpha suborder of Psocoptera.

Lice and humans

Humans host three different kinds of lice: head lice, body lice (which live mainly in clothing), and pubic lice. The DNA differences between head lice and body lice provide corroborating evidence that humans started wearing clothes about 72,000 years ago, give or take 42,000 years.

Recent DNA evidence suggests that pubic lice spread to humans approximately 3,000,000 years ago from the ancestors of humans by sharing the same bed or other communal areas with them, and are more closely related to lice endemic to gorillas than to other lice species which infest humans.

Adult and nymphal lice can survive on sheep-shearers' moccasins for up to 10 days, but microwaving the footwear for five minutes in a plastic bag will kill the lice.

Lice infestations can be controlled with lice combs, and medicated shampoos or washes.

Gallery

Image:Ricinus bombycillae (Denny, 1842).JPG|Ricinus bombycillae, an Amblyceran louse from the bohemian waxwingImage:Trinoton anserinum (Fabricius, 1805).JPG|Trinoton anserinum, an Amblyceran louse from a mute swan.Image:Lice image01.jpg|Damalinia limbata is an Ischnoceran louse from goats. The male is smaller than the female.Image:Louse_diagram,_Micrographia,_Robert_Hooke,_1667.jpg|Diagram of a louse, by Robert Hooke, 1667.


See also



Notes

  1. Sheep parasites Retrieved on 10 November 2008


External links




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