Coloured scanning electron micrograph (SEM) of Human head louse on human hair (Pediculus humanus capitis). The head louse (Pediculus humanus capitis) is an insect in the Order Psocodea (parasitic lice, formerly Order Phthiraptera/Pscocptera). Head lice are ectoparasites with humans as the only host. A head louse must feed on blood several times daily and resides close to the scalp to maintain its body temperature. Infestation with head lice is common and occurs worldwide, especially in children. Head lice are not the vectors of any known diseases. Only rare secondary infections occur from scratching the bites. Magnification: x10 when shortest axis printed at 25 millimetres.