Pediculus humanus
human lice

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).

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)

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)

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)

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, Bashir, and Maibach, 08/12/2000; Leftwich, 1977)

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)

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)

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