Blood meal for a head louse. Macrophotography close-up footage of the head and gut of a human head louse (Pediculus humanus capitus) on human hairs, feeding on blood (red). Head lice are wingless insects measuring 2-3 millimetres in length. They live on head hair, laying eggs and sucking blood from the scalp. This causes intense itching, provoking scratching that can lead to scalp inflammation or dermatitis.