1. A small insect which lives on the bodies of animals and people: One of the problems for children in schools is the transference of head lice to each other.
2. Informally, a cruel or a bad person: Fern's husband has a reputation of being a real louse.

Lice and the loss of body hair by humans

One of the more embarrassing mysteries of human evolution is that people are host to, or may be host to, no fewer than three kinds of lice while most animal species have just one kind of louse.

Even bleaker for the human reputation, the pubic louse, which gets its dates and residence-swapping opportunities when its hosts are locked in intimate embrace, does not seem to be a true native of the human body. Its closest relative is the gorilla louse. (Don't even think about it!)

Three kinds of louse call Homo sapiens their home, but each occupies a different niche on the human body.

• The head louse, Pediculus humanus, lives in the forest of fine hairs on the human scalp.
• Its cousin, the body louse, lives not on the skin but in clothes.
• The exclusive territory of the pubic louse, Phthirus pubis, is the coarser hairs of the crotch.

Biologists have long been scratching their heads over the fact that the human head louse is a sister species to the chimpanzee louse, but the pubic louse is closely related to the gorilla louse.