Animal Diversity Web

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).

• Biogeographic Regions
• nearctic
  • native
• palearctic
  • native
• oriental
  • native
• ethiopian
  • native
• neotropical
  • native
• australian
  • native
• oceanic islands
  • native

• Other Geographic Terms
• cosmopolitan

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)

• Other Physical Features
• ectothermic
• heterothermic
• bilateral symmetry

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)

• Key Behaviors
• parasite
• sedentary
• solitary

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)

• Primary Diet
• carnivore
  • sanguivore

• 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

• IUCN Red List

  No special status

• US Federal List

  No special status

• CITES

  No special status

Contributors

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

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.