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Louse

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Descripton

Anoplura Rhyncophthirina Ischnocera Amblycera

Louse (plural: lice) is the common name for members of over 3,000 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.

Contents

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 animals, 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 exopterygotes, being born as miniature versions of the adult, known as nymphs. The young moult three times before reaching the final adult form, usually within a month of hatching.

Ecology

Lice are optimal model organisms to study the ecology of contagious pathogens since their quantities, sex-ratios etc. are easier to quantify than those of other pathogens. The ecology of avian lice has been studied more intensively than that of mammal lice.

A few major trends

A few effects of lice infestation upon the host

Classification

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 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

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

Lice in humans

Humans host three different kinds of lice: head lice, body lice, and pubic lice. Lice infestations can be controlled with lice combs, and medicated shampoos or washes.

Human lice and DNA discoveries

Lice have been the subject of significant DNA research in the 2000s that led to discoveries on human evolution. For example, genetic evidence suggests that our human ancestors acquired pubic lice from gorillas approximately 3-4 million years ago. Additionally, the DNA differences between head lice and body lice provide corroborating evidence that humans started losing body hair about 2 million years ago.[dead link]

The mitochondrial genome of the human species of body lice (Pediculus humanus humanus), the head louse (Pediculus humanus capitis) and the pubic louse (Pthirus pubis) is fragmented into a number of minichromosomes. This fragmentation appears to have been present for at least 7 million years. The body louse evolved from the head louse ~107,000 years ago.

Gallery

  • Ricinus bombycillae, an Amblyceran louse from the bohemian waxwing
  • Trinoton anserinum, an Amblyceran louse from a mute swan.
  • Damalinia limbata is an Ischnoceran louse from goats. The male is smaller than the female.
  • Diagram of a louse, by Robert Hooke, 1667.

Ricinus bombycillae, an Amblyceran louse from the bohemian waxwing

Trinoton anserinum, an Amblyceran louse from a mute swan.

Damalinia limbata is an Ischnoceran louse from goats. The male is smaller than the female.

Diagram of a louse, by Robert Hooke, 1667.

References

Louse


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