Pediculus Pubis. The crab-louse is gray-black and is a much broader square form than the other two species of louse, that has been a great scourge to soliders in time of war. This insect has been named the crab-louse from its broad crab-like appearance. It is of grayish color; the head is small, and appears to be united with the broad body without any thorax; it inhabits the hairy part of the body, under the arms or shoulders, in the beard, etc., but appears to avoid the head. These insects pierce deeply into the skin of mankind, and produce an intolerable itching.