Crabs are related to head and body lice. But these lice are found mostly in the pubic hair. They sometimes move to the hair on other parts of the body, such as the beard, mustache, eyelashes and underarms.
Lice live by feeding on human blood.
They are small but they can be seen and easily recognized. Burrows are usually found between the fingers, around the genitals, on the wrists or buttocks, and under the arms. By direct contact, usually sexual, with someone that is infested. Sometimes you can get them from an infested person's towels and clothing. The first signs of crabs is usually severe itching in the genital or anal area.