Pediculus humanus

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Geographic Range

Human lice can be found anywhere on the planet that is populated by humans. They are more prevalent in areas where people change or wash their clothing infrequently and/or are unclean themselves (Milne and Milne 1980).

Habitat

The habitat of the human louse is solely on the human body or in the clothes. They are rarely found elsewhere because they can only survive away from the host for a few days.

(Milne and Milne 1980)

Physical Description

Pediculus humanus is a small insect with a large abdomen and legs equipped with sharp claws for holding onto hair and clothing fibers. The head of the louse ia slightly narrower than the body. They do not have wings like most insects, but they have piercing mouthparts for digging into the skin and draining out the blood. The head louse, Pediculus humanus capitis, is normally 1-2 mm long, while the body louse, Pediculus humanus humanus, also known as the "cootie" is usually slightly larger, 2-3.5 mm. The "nits," or eggs, of the louse are about 1 mm long and about half as wide. The young lice are often called "red backs," due to the red color they are because of the blood in them. They turn a grey color once digestion takes place, and is where they get the name "gray back". (Grzimek, 1972; Leftwich, 1977; Milne and Milne, 1980; Roberts and Janovy Jr., 2000)

Reproduction

The female lice lay their eggs, which are called nits, singly on the hairs of the host (if they are head lice) or attached to clothing in the case of body lice. The nits will hatch into nymphs in about eight days. The nymphs also suck blood and mature in eight to sixteen days. Each adult female body louse produces between two and three hundred nits in her lifetime, and a single female head louse produces between eighty and one-hundred. Due to this fact and that the generations follow at about three week intervals, a single female could inundate a host in a matter of months (Burton 1968, Grzimek 1972).

Behavior

There are very few morphological differences between the two sub-species. The main thing that keeps them separated is their behavior. Body lice live and hide in the folds of the clothing of the hosts, usually close to the skin. They will normally only crawl on the skin in order to feed. Head lice live on the scalp, either attached to the scalp while feeding or to the hairs.

The lice are transmitted from one person to another by direct contact, by clothes or a brush, or by fallen hair. Anything that has a nit or a female on it will transmit the infestation.

In the case of head lice, the females are actually specific about the part of the head where they lay their eggs. They prefer to lay them behind the ears or on the back of the head, near the neck line. (Grzimek, 1972; Milne and Milne, 1980; Roberts and Janovy Jr., 2000)

Food Habits

Lice are obligate ectoparasites. They live off of the blood of humans. They have specially designed mouth parts for piercing the skin of humans and retrieving the blood that is present. (Chew, et al., 08/12/2000; Leftwich, 1977)

  • Animal Foods
  • blood

Economic Importance for Humans: Positive

The only way that this species could have any positive economic benefit would be to the people that are involved with selling the drugs and tools used to get rid of an infestation. Today, Lindane, permethrin, and malathion are used to kill the lice. Fine toothed combs are also used in a technique called wet combing, but this is usually accompanied with the use of one of the previously mentioned chemicals.

(Chew et. al. 2000)

Economic Importance for Humans: Negative

P. humanus has relatively little direct effect on its hosts. Bites itch, but do not generally cause other harm. However, lice can be vectors for important diseases. The three most important diseases they can carry are typhus, trench fever (both caused by bacteria in the genus Rickettsia), and relapsing fever (caused by another bacteria species Borrelia recurrentis). These bacterial diseases can now be treated successfully with antibiotics, but in the past, they caused the death of millions of people. Major epidemics strongly affected the political and economic history of Europe and Asia, and liice were the main agents in the spread of these diseases.

Lice cannot withstand high temperatures, so washing can eradicate the lice. Not until the practice of washing and changing our clothes on a regular basis have we been able to slow the spread of lice, and the diseases that they carry. In contrast to this, their occurrence increases greatly in time of war and hardship because people are closely packed and hygiene is not of high importance.

(Grzimek 1972; Roberts and Janovy 2000; Milne and Milne 1980)

Conservation Status

Contributors

Chris Morgan (author), Southwestern University, Stephanie Fabritius (editor), Southwestern University.

Glossary

Australian

Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

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Ethiopian

living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

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Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

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Neotropical

living in the southern part of the New World. In other words, Central and South America.

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Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

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bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

cosmopolitan

having a worldwide distribution. Found on all continents (except maybe Antarctica) and in all biogeographic provinces; or in all the major oceans (Atlantic, Indian, and Pacific.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

native range

the area in which the animal is naturally found, the region in which it is endemic.

oceanic islands

islands that are not part of continental shelf areas, they are not, and have never been, connected to a continental land mass, most typically these are volcanic islands.

oriental

found in the oriental region of the world. In other words, India and southeast Asia.

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parasite

an organism that obtains nutrients from other organisms in a harmful way that doesn't cause immediate death

sanguivore

an animal that mainly eats blood

sedentary

remains in the same area

solitary

lives alone

References

Burton, J. 1968. The Oxford Book of Insects. Great Britain: University Press.

Chew, A., S. Bashir, H. Maibach. 08/12/2000. Treatment of head lice. Lancet, 9229: 523-524.

Grzimek, B. 1972. Animal Life Encyclopedia. New York: Van Nostrand Reinhold Company.

Leftwich, A. 1977. A Dictionary of Entomology. New York: Crane Russak and Company, Inc..

Milne, L., M. Milne. 1980. The Audubon Society Field Guide to North American Insects and Spiders. 1980: Alfred A. Knopf.

Roberts, L., J. Janovy Jr.. 2000. Gerald D. Schmidt and Larry S. Roberts' Foundations of Parasitology, 6th Edition. Burr Ridge, Illinois, USA: McGraw Hill.