Head lice. Coloured scanning electron micrograph (SEM) of head lice (Pediculus humanus capitis). The head louse is parasitic insect which inhabits the hair of the head, gluing its eggs (called nits) to the shafts of individual hairs. It lives on blood, which it sucks from the scalp. The wounds left by the lice cause intense itching, which can lead to dermatitis and infection. The problems are compounded by reflex scratching of the bites. The lice can spread from head to head by close contact. Lice and nits can be killed with medicated shampoos. Magnification: x10 when printed 10 centimetres wide.