(Latin: Phthirius pubis)
A crab louse is almost as broad as it is long. Its ‘claws’ are extraordinarily well developed and together with the shape of the body give it a crab-like appearance. Its preferred habitat is among the body hairs and particularly among the pubic hairs.
The large claws are well adapted for gripping these very strong hairs. Crab lice can also occur in the armpits, in beards and sometimes on eyelids and eyebrows, and indeed they have even been found among the very fine hair on the heads of infants.
A female crab louse lays about 25 eggs, each firmly fixed to its own hair. The development from egg to adult takes about three weeks.
Crab lice are sedentary. Having found a suitable place a louse will seize the host’s hair, bore into the skin with its mouth parts and suck blood several times in succession, with only short intervals. It will die within about a day if removed from its host. There is no doubt that crab lice are mostly transmitted from one human to another during sexual intercourse. There are, however, records of small children carrying crab lice, so they can be transmitted by other means.