Definitions

louse

louse

[n. lous; v. lous, louz]
louse, common name for members of either of two distinct orders of wingless, parasitic, disease-carrying insects. Lice of both groups are small and flattened with short legs adapted for clinging to the host.

The sucking lice, of the order Anoplura, are external parasites of humans and other mammals, feeding on blood by means of their piercing-and-sucking mouthparts. The group includes the body lice and head lice, considered varieties of the same species, Pediculus humanus, and the crab, or pubic, louse, Phthirus pubis, named for its crablike appearance. A female sucking louse lays about 300 eggs, or nits, in her lifetime, cementing them to body hairs and underclothing. The larva resembles the adult; the life cycle takes about 16 days. Sucking lice infestations are common in crowded living conditions and where clothing is not changed or washed frequently. Body lice may transmit rickettsial diseases (see rickettsia) and bacterial infections such as relapsing fever; infection results from scratching the crushed louse or its feces into the skin.

The chewing, or biting, lice, of the order Mallophaga, have chewing mouthparts and feed on hair, skin, or feather fragments of the host. They attack birds, rodents, and domesticated animals. Although they do not actually puncture the skin, and thus are scavengers and not true parasites, they often multiply so rapidly that they irritate, weaken, and may even kill the host. The chicken louse, Menopon pallidum, if left uncontrolled, can be a major problem in poultry production. Chewing lice may produce 6 to 12 generations annually. The eggs hatch into rapidly developing young in which metamorphosis is incomplete, as in many parasites.

The book louse is a tiny, wingless, cosmopolitan insect that damages books by feeding on glue, paste, and paper. It resembles lice but is not related, belonging to the order Psocoptera. The aphid is sometimes called plant louse.

Lice are classified in the phylum Arthropoda, class Insecta, orders Anoplura and Mallophaga.

See bulletins of the U.S. Dept. of Agriculture.

Any of more than 400 species (suborder Anoplura, order Phthiraptera) of small, wingless, flat ectoparasitic insects found worldwide. They have piercing and sucking mouthparts for extracting their food of mammals' blood and tissue fluids. The nymphs mature after several molts. Species are host-specific: Pediculus infests humans (see human louse), whereas other sucking lice (genera Haematopinus and Linognathus) attack domestic animals, such as hogs, cattle, horses, and dogs.

Learn more about sucking louse with a free trial on Britannica.com.

Any of several species of sapsucking, soft-bodied insects (order Homoptera) that are about the size of a pinhead, with tubelike projections on the abdomen. Serious plant pests, they stunt plant growth, produce plant galls, transmit plant viral diseases, and deform leaves, buds, and flowers. Ants may take care of aphids, protecting them from weather and natural enemies and transferring them from wilted to healthy plants. The ants in turn obtain honeydew, a sweet product excreted by aphids, which the ants retrieve by “milking” the aphids (stroking their abdomens).

Learn more about aphid with a free trial on Britannica.com.

Any of some 3,300 species of small, wingless, parasitic insects of the order Phthiraptera. The order consists mainly of biting, or chewing, lice (parasites of birds and mammals) and sucking lice (see sucking louse). The louse's body is flattened. The eggs, or nits, are cemented to the hair or plumage of the host, and most species spend their entire lives on the bodies of host animals. Heavy infestations cause much irritation and may lead to secondary infections. In moving from host to host, lice may spread many diseases, including tapeworm infestation in dogs and murine typhus in rats.

Learn more about louse with a free trial on Britannica.com.

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 are reflected in their size (0.5–8 mm), stout legs, and claws which are adapted to cling tightly to hair, fur and feathers, and that they are wingless and dorsoventrally flattened.

Lice feed on skin (epidermal), 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. They mostly like clean hair.

A louse's 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. Living lice eggs tend to be pale white. Dead lice eggs are more yellow. Lice are very annoying and are difficult to remove, but not impossible. Lice infestations can be controlled with lice combs, and medicated shampoos or washes.

Classification

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:

It has been suggested that the order is contained by the Troctomorpha suborder of Psocoptera. Lice can not jump or fly.

Lice and humans

Humans are unique in that they 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 at approximately 70,000 BC..

Recent DNA evidence suggests that pubic lice spread to the ancestors of humans approximately 3.3 million years ago from the ancestors of gorillas 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 infesting humans.

Gallery

References

See also

External links


Search another word or see louseon Dictionary | Thesaurus |Spanish
Copyright © 2014 Dictionary.com, LLC. All rights reserved.
  • Please Login or Sign Up to use the Recent Searches feature