Chewing and Sucking Lice: Phthiraptera

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Lice are small, flattened, wingless insects measuring 0.01 to 0.4 inches (0.3 to 11 millimeters) in length. Females are typically larger than males. Many species are pale whitish or yellowish, while other species are brown or black. Some species have color patterns that help them to blend in with the fur or feathers of the animal on which they live. Their heads are broad and blunt to narrow with a snout. They have short antennae (an-TEH-nee), or sense organs, with only three to five segments, and no simple eyes. Compound eyes, eyes with multiple lenses, are either very small or absent. The mouthparts are directed forward. Chewing lice have well-developed jaws that either open from side to side or up and down. In most sucking lice the jaws are entirely absent, although some species have greatly reduced jaws inside their heads. The abdomen has eight to ten segments, depending on the species.

The flattened bodies are perfect for moving in the narrow spaces between feathers and fur, and the short, strong legs have one or two claws that help them to cling. The legs of most sucking lice have a single claw that clamps onto hair shafts. This reduces their chances of being removed when the animal cleans and grooms itself.


Chewing and sucking lice are found on all continents, including Antarctica. The distribution of lice is roughly similar to that of the birds and mammals on which they live. However, their distribution within the host population is not uniform. They are usually quite patchy or concentrated in some areas. There are 4,927 species of lice worldwide, with about 780 species in the United States and Canada.


Chewing and sucking lice are ectoparasites (EHK-teh-PAE-rih-saits), organisms that live on the outside of their host organism. All species spend their entire lives on the body of the host animal. They require the constant temperature and moisture of this habitat to feed and reproduce. Most species of lice are found only on a single kind of host or on small groups of closely related species.

More than 4,300 species of chewing lice have been found on 3,910 different kinds of animals, including 3,508 species of birds and 402 species of mammals. All orders and most families of birds have chewing lice. Five hundred and forty-three species of sucking lice have been found on 812 species of mammals. Mammals that do not have lice include bats, whales, dolphins, dugongs, manatees, pangolins, echidnas, and platypuses.

Although the host body would seem to be a uniform habitat, it is actually a series of smaller habitats that differ slightly in terms of temperature and moisture. For example, the different parts of a bird's body, such as the head, back, wings, and rump, are completely different habitats from the viewpoint of a louse. These different habitats might allow several species of lice with slightly different temperature and humidity requirements to live on the same host animal without having to compete with one another directly for food and space. Some species occupy more than one part of the body at different times in their lives. For example, a species of lice live inside the throat pouches of pelicans and cormorants where they feed on blood. However, they must return to the head feathers to lay their eggs.


The sucking lice feed exclusively on the blood of mammals. They use their mouthparts to pierce the skin of their host and suck up blood from the small blood vessels located near the skin surface. Chewing lice use their biting mouthparts to feed on feathers, hair, bits of skin, dried blood, and other skin secretions.


Most louse species remain attached to their host for their entire lives. Their populations vary greatly in size and are strongly influenced by the condition and health of their hosts. For example, birds with damaged bills or feet may have more lice because they are unable to preen or clean themselves efficiently. Some lice escape preening by wedging themselves between feather barbs or by living at the bases of fluffy feathers on the bird's abdomen. They will bite into the feathers with their mouthparts and lock their jaws in place. Some species go to the extreme of actually living inside the quills of wing feathers to escape preening by their shorebird hosts. The dead, dried bodies of lice are found firmly attached to bird and mammal skins in museum collections, sometime hundreds of years after the collection and death of their host.

Direct physical contact between hosts is usually the best way for lice to disperse within a host species population. Host animals also pick up new lice by sharing nests and nest materials with other infested animals. One of the most unusual and rare methods of louse dispersal is by means of phoresy (FOR-uh-see), or hitchhiking. These lice attach themselves to the abdomens of certain flies and hitch a ride to the next host.


The extinction of a bird or mammal species leads directly to the extinction of many of their parasites. Nearly 370 species of birds and mammals are listed by the IUCN as Extinct in the Wild or Critically Endangered. At least fifty species of lice share their fate, yet none appear on any list. By 1990 at least eight species of lice had already followed their host birds and mammals to extinction.

For most species of lice, it is known that there are both males and females and they reproduce primarily by mating. A few species reproduce by parthenogenesis (PAR-thuh-no-JEH-nuh-sihs), a process where the young develop from unfertilized eggs. Females glue their whitish eggs, also known as nits, to parts of feathers or hair shafts. Human body lice will sometimes attach eggs to clothing fibers that stick from the garment like hairs. Eggs usually take four to ten days to hatch depending on species and temperature. The larvae (LAR-vee), or young of an animal that must change form before becoming adults, closely resemble the adults but are incapable of reproducing. They develop gradually through a series of molts, shedding their exoskeletons or hard outer coverings four times before reaching adulthood. Adult lice live for about a month. Human body lice will lay 50 to 150 eggs in their lifetime.


The human body and head louse carries and spreads bacteria that cause the diseases louse-borne typhus, trench fever, and louse-borne relapsing fever. Louse infestations commonly occur among the homeless, or persons in refugee camps and other crowded conditions that result from war and natural disasters. Head lice are common among school children around the world. They are passed from one host to the next through infested clothing. Pubic lice, also known as "crabs," are normally spread through very close, personal contact by grownups.

Lice also infest domesticated mammals and poultry. Infested animals and louse control cost farmers and breeders hundreds of millions of dollars every year in lost production and the purchase of expensive chemical controls. For example, infested chickens will lay fewer eggs, resulting in less money earned by poultry farmers. Chemical pesticides are commonly used to kill lice on poultry and livestock. However, there are concerns over the safety of using these chemicals on large numbers of animals on a regular basis. There is also evidence that some lice are becoming resistant to pesticides. Louse resistance to pesticides was noted by the fact that fewer and fewer lice are killed with each application of the same amount of chemical.


Only one species of louse is listed by the World Conservation Union (IUCN). The pygmy hog louse is listed as Endangered or facing a very high risk of extinction in the wild. Its host, the pygmy hog of India, is also listed as Endangered.


Physical characteristics: The body of this louse is gray, longer than wide, and measures 0.078 to 0.12 inches (2 to 3 millimeters) in length. The head has distinctive dark eyes. Their abdomens lack distinct bumps. The head louse is usually 20 percent smaller than the body louse.

Geographic range: This species is found worldwide. It is an ectoparasite of humans but is also found on gibbons and New World monkeys.

Habitat: Two forms exist. Head lice are found on the human scalp. Body lice prefer clothing and the human chest and stomach.

Diet: Both head and body lice feed on blood.

Behavior and reproduction: Head lice feed regularly every few hours, while body lice feed only once or twice per day when the host is resting. Both forms are capable of adapting to the different ecological conditions on the human scalp, body, or clothing. They carry several important human diseases.

Head lice attach their eggs to the base of hair shafts. Body lice glue their eggs to hairlike fibers of clothing worn by the host. Eggs hatch in five to seven days. The larvae reach adulthood in ten to twelve days.

Human head/body lice and people: This species, also known as cooties or gray backs, was called "mechanized dandruff" by American soldiers during World War II. The body louse spread epidemic typhus that resulted in the death of hundreds of millions of people up to the early 1900s. Since World War II, large outbreaks of this disease have occurred in Africa, mostly in Burundi, Ethiopia, and Rwanda. The head louse can be common in children. Up to one out of five students are infested in some primary schools in parts of Australia, the United Kingdom, and the United States. Head lice are not normally known to transmit disease.

Conservation status: This species is not endangered or threatened. However, populations found on small, isolated human tribes and non-human hosts are probably threatened with extinction due to declining host populations and habitat loss. ∎


Physical characteristics: The slender pigeon louse is a long, slender louse with two bladelike hairs near the front of its head. The threadlike antennae are five-segmented. They measure 0.078 to 0.12 inches (2 to 3 millimeters) in length.

Geographic range: This louse is only found on four species of pigeons, including the widely distributed rock dove or city pigeon. Rock doves (and their ectoparasites) live with humans and have been introduced throughout the world. The distribution of the slender pigeon louse is thought to match that of the rock dove.

Habitat: They are found only among the feathers on the upper and lower sides of the wings of pigeons.

Diet: Slender pigeon lice eat the fluffy parts of the feathers.

Behavior and reproduction: The slender body of this louse allows it to move in between the feather barbs. They grab the edges of feather barbs with their jaws to avoid the preening activities of the host.

Females attach their eggs on the underside of the wing feathers near the pigeon's body. They hatch in three to five days at 98.6°F (37°C).

Slender pigeon lice and people: They are used as research animals by scientists studying how animals change over time and how they interact with parasites.

Conservation status: This species is not endangered or threatened. However, populations present on the Pale-backed Pigeon from Central Asia and the Middle East should be considered vulnerable, or at high risk of extinction in the wild. ∎



Kim, K. C., H. D. Pratt, and C. J. Stojanovich. The Sucking Lice of North America. University Park: Pennsylvania State University Press, 1986.


Conniff, R. "Body Beasts." National Geographic 194, no. 6 (December 1998): 102–115.

Price, M. A., and O. H. Graham. "Chewing and Sucking Lice as Parasites of Mammals and Birds." USDA Agricultural Research Service Technical Bulletin 1849 (1997): 1–309.

Web sites:

National Pediculosis Association. (accessed on October 6, 2004).

Phthiraptera Central. (accessed on October 6, 2004).

Phthiraptera. Lice. (accessed on October 6, 2004).

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Chewing and Sucking Lice: Phthiraptera

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