Pubic lice (Pthirus pubis) are yellow-gray parasites found in the pubic region and transmitted by sexual contact. They are only 1.1 to 1.8 millimeters long and are also called crab lice, or crabs, because of their shape and the crab-like claw-like front legs with which they cling to hair. Sometimes pubic lice may be found in other areas of the body containing coarse hair, such as armpits or the chest.