Pubic lice (Phthirus pubis) are one of the many varieties of lice (singular "louse") specialized to live on different areas of different animals. As the name implies, pubic lice are specialized to live in the human pubic hair, but may also live in hair on other areas of the body such as hair on the legs, armpit, mustache, beard, eyebrows, and eyelashes. Infestations of young children are usually on the eyebrows or eyelashes. Lice found on the head are not pubic lice; they are head lice.
Public lice have legs that are spaced further apart than head lice, this is an adaptation that enables them to move around more easily in their habitat.
The pubic louse is somewhat crab-shaped, hence its slang name of "crabs".
The female louse glues her eggs, called "nits", which look like tiny white beads, to hair shafts.
There are three stages in the life of a pubic louse: the nit, the nymph, and the adult.
- Nit: Nits are pubic lice eggs. They are hard to see and are found firmly attached to the hair shaft. They are oval and usually yellow to white. Nits take about 1 week to hatch.
- Nymph: The nit hatches into a baby louse called a nymph. It looks like an adult pubic louse, but is smaller. Nymphs mature into adults about 7 days after hatching. To live, the nymph must feed on blood.
- Adult: The adult pubic louse resembles a miniature crab when viewed through a strong magnifying glass. Pubic lice have six legs, but their two front legs are very large and look like the pincher claws of a crab; this how they got the nickname "crabs." Pubic lice are tan to greyish-white in color. Females lay nits; they are usually larger than males. To live, adult lice need to feed on blood. If the louse falls off a person, it dies within 1-2 days.
Pubic lice are normally spread by sexual contact and are considered a sexually transmitted disease, but can also be spread by sharing clothes or bedding. A common misbelief is that infestation can be spread by sitting on a toilet seat. This isn't likely, since lice cannot live long away from a warm human body. Also, lice do not have feet designed to walk or hold onto smooth surfaces such as toilet seats.
Pubic lice are easily killed by a 1% permethrin or pyrethrin lice shampoo, but the pubic hair must be combed with a fine-toothed comb after treatment to remove the nits. Lice can survive in bedding and clothing, so these items must be treated, sterilized, or contact with them must be avoided for two weeks, after which time any lice will have died. Lindane (1%), another pediculocide, is not recommended for pregnant or nursing women or for children less than 2 years old.