Lice are small, flattened, wingless insects. There are three species which are exclusively human ectoparasites: (1) Pediculus humanus var. capitis, head louse, (2) Pediculus humanus var. humanus, body louse, and (3) Phthirus pubis, crab louse.
Body and head lice have a similar morphology and can interbreed. They have an elongated abdomen and are 2 – 3mm in length. The crab louse has a much shorter abdomen and measures about 1mm. They have distinctive heavy claws.
Lice deposit their eggs, called ‘nits’, on hair or fibers of clothing where they are firmly attached. The eggs hatch in 5 – 11 days emerging as nymphs. These undergo three molts within 2 weeks. The life span of the adult is approximately 1 month. The number of eggs deposited during the lifetime has been estimated at 300 for the body louse, 140 for the head louse, and 50 for the crab louse.
All three kinds of lice have mouth parts which easily pierce the skin. They suck blood for long periods. The body and head lice can survive for a week without food, but the crab louse dies in 2 days. The irritating saliva, injected during feeding, causes localized inflammation and itching. Scratching can increase the inflammation, and can lead to secondary bacterial infection.
Click on the following levels to learn more about each type of lice infection:
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