Pubic louse. Scanning electron micrograph (SEM) of the pubic louse, Phthirus pubis, also known as the crab louse clinging to a pubic hair. An infestation of P. pubis causes pediculosis, the symptoms of which are severe itching and rash. The lice suck blood, feeding 5 times a day. They spread through sexual contact and via bedding or clothing. Each of the louse's 6 legs terminates in a massive claw, which folds inward to meet a thumb-like projection on the opposite side. The louse climbs and swings through hair, locking into position when disturbed, for instance by scratching or washing. Magnification: x50 when printed at 10 centimetres across