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

Louse (plural: lice) is any of the small, wingless, dorsoventally flattened insects comprising the neopteran order Phthiraptera. This order of over 3,000 species consists mostly of biting, chewing, or sucking members that are obligate external parasites or scavengers on birds and mammals.

Also known as fly babies, every avian order and most mammalian orders are infected with these parasites. However, 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).

Three of the sucking lice of the suborder Anoplura are well-known external parasites on humans: Pediculosis humanus capitis (head lice), Pediculosis humanus corporis (body lice), and Phthirus pubic (pubic lice). While lice infestations are not dangerous by themselves, they can be a serious health problem given that some lice can be vectors carrying organisms that cause other diseases, such as trench fever, epidemic typhus, and relapsing fever (Frey 2002).

Historically, the lice have been divided into two main groups, the sucking lice of the suborder Anoplura and the chewing lice of the order Mallophaga. However, Mallophaga now is considered to be paraphyletic and generally the Phthiraptera now are divided into four suborders (ITIS 2004; ITIS 2007).

The term lice often is used more generally for parasitic animals that are not part of Phthiraptera, such as fish lice, which are a group of parasitic crustaceans, and book lice, which are insects that received their name from feeding on the paste used in binding books.

Description

As lice spend their entire lives on the host, they have developed adaptations that enable them to maintain close contact with the host. These adaptations are reflected in their tiny size (0.5 to 8 millimeters), stout legs and claws that are adapted to cling tightly to hair, fur, and feathers, and a wingless and dorsoventrally flattened body.

Lice feed on skin (epidermal) debris, feather parts, [Chlorine] sebaceous secretions, and blood. A louse's color varies from pale beige to dark gray; however, if feeding on blood, it may become considerably darker.

A louse's egg is commonly called a nit. Lice attach their eggs to their host's hair with specialized saliva that 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.

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 recognized (ITIS 2007; ITIS 2004):

• 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
• Amblycera: Jumping Lice have very strong hind legs and can jump a distance of three feet

Lice and humans

Humans are unique in that they host three different kinds of lice: head lice (Pediculosis humanus capitis), body lice (Pediculosis humanus corporis, which live mainly in clothing), and pubic lice (Phthirus pubic). All three are members of the Anoplura suborder, and contain sucking mouthparts allowing them to feed on human blood and lay their eggs on the human body or on clothing.

Lice infections are known as pediculosis and includes infections of the skin, hair, or genital region caused by lice living directly on the body or on clothing (Frey 2002). The Latin name for louse is the source of the name pediculosis (Frey 2002).

Head lice. The head louse (Pediculus humanus capitis) is an obligate ectoparasite of humans that spend their life on human scalps and feed exclusively on human blood (Buxton 1947). Humans are the only known host of this parasite (Buxton 947). Transmission from person to person can occur by the sharing of combs, hats, or hair brushes, with epidemics common among school-age children (Frey 2002). The head lice is about (convert|0.06|inch|cm}} of an inch in length. The adult form visible on the scalp and especially around the ears (Frey 2002).

Body lice.

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

Wikimedia Commons has media related to:

Phthiraptera

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  The chewing louse Damalinia limbata is found on Angora goats. The male louse (right) is typically smaller than the female (left), whose posterior margin of the abdomen is more rounded than those of male lice.

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  Diagram of a louse, by Robert Hooke, 1667.

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  Trichodectes canis, the biting dog louse

References

ISBN links support NWE through referral fees

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• Frey, R.J. 2002. Lice infestation. Pages 1994-1996 in J.L. Longe (ed.), The Gale Encyclopedia of Medicine, 2nd edition, volume 3. Detroit: Gale Group/Thomson Learning. ISBN 0787654922.

• Integrated Taxonomic Information System (ITIS). 2004. Phthiraptera Haeckel, 1896 ITIS Taxonomic Serial No.: 624282. Retrieved August 14, 2008.

• Integrated Taxonomic Information System (ITIS). 2007. Mallophaga ITIS Taxonomic Serial No.: 103337 . Retrieved August 14, 2008.

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