louse

Phthiraptera
Light micrograph of Fahrenholzia pinnata
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Subclass:	Pterygota
Infraclass:	Neoptera
Order:	Phthiraptera Haeckel, 1896
Suborders
Anoplura Rhyncophthirina Ischnocera Amblycera

Lice (singular: louse), (order Phthiraptera) are an order of over 3,000 species of wingless insects; three of which are classified as human disease agents. They are obligate ectoparasites of every avian and most mammalian orders. They are not found on Monotremes (the platypus and the echidnas or spiny anteaters) and a few eutherian orders, namely the bats (Chiroptera), whales, dolphins and porpoises (Cetacea) and pangolins (Pholidota).

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 0.5 to 8 millimetres (0.020 to 0.31 in), 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 antennae, 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.^[1]

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.^[1]

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.^[1]

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, which they usually reach within a month of hatching.^[1]

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 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

It has been suggested^{[weasel words]} that the order is contained by the Troctomorpha suborder of Psocoptera.

Lice and humans

World War II-era American poster, created to prevent the transmission of lice between servicemen.

For information about human infestation, see Pediculosis. For information on treatment see Treatment of human head lice.

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.^[2]

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.^[3]

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.^[4]

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

Gallery

Wikimedia Commons has media related to: Phthiraptera

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

See also

• Pest (organism)
• Use of DNA in forensic entomology
• Whale louse, unrelated crustaceans that live parasitically on marine mammals

External links

Look up louse in Wiktionary, the free dictionary.

• Lice Pest Control Information - National Pesticide Information Center
• Bed-hopping led humans to 3 million-year itch
• www.phthiraptera.org has extensive scientific information.
• body and head lice on the University of Florida/Institute of Food and Agricultural Sciences Featured Creatures Web site
• crab louse on the University of Florida/Institute of Food and Agricultural Sciences Featured Creatures Web site
• WebMD Lice Info
• Lice chapter in United States Environmental Protection Agency‎ and University of Florida/Institute of Food and Agricultural Sciences National Public Health Pesticide Applicator Training Manual
• Pediculus humanus capitis head louse facts, myths, life cycle at MetaPathogen