The claws of crab lice are not suited for attaching to coarse body hair such as pubic hair. They are dependent on human blood, but can live up to 24 hours off their host. Crabs feed by inserting their mouthpieces into small blood vessels in the skin and sucking blood. The infection person then begin scratching which causes redness, irritation, and inflammation of the skin. Crabs and their eggs are usually visible to the eye.
Sexual transmission is the primary means of transmission, but non-sexual transmission also occurs.
Crabs are easily transmitted non-sexually through the sharing of infested bedding or intimate clothing. Contracting crabs from infested toilet seats, couches and chairs is possible but extremely rare. Some crabs are usually visible, no laboratory test is necessary. Diagnosis is made by a physical exam. Both the lice and the eggs must be killed.