Crab louse. Coloured Scanning Electron Micrograph (SEM) of the crab louse Phthirus pubis, also known as the pubic louse. It is an external parasite of humans, living in pubic hair. The small head of the louse is seen (at top) with biting, blood- sucking mouthparts. There are six legs, each with a massive claw which folds inward to meet a thumb- like projection on the opposite side. Using these legs the louse climbs through pubic hair, locking into position when disturbed. Infestation by Phthirus pubis causes pediculosis, with symptoms of a severe itching rash. The louse sucks blood. It is spread by sexual contact, in bedding or in clothing. Magnification: x40 at 6x7 cm size. x60 at 4x4"~PORTRAIT"