<P> The head louse (Pediculus humanus capitis) is an obligate ectoparasite of humans that causes head lice infestation (pediculosis capitis). </P> <P> Head lice are wingless insects spending their entire lives on the human scalp and feeding exclusively on human blood . Humans are the only known hosts of this specific parasite, while chimpanzees host a closely related species, Pediculus schaeffi . Other species of lice infest most orders of mammals and all orders of birds, as well as other parts of the human body . </P> <P> Lice differ from other hematophagic ectoparasites such as fleas in spending their entire lifecycle on a host . Head lice cannot fly, and their short, stumpy legs render them incapable of jumping, or even walking efficiently on flat surfaces . </P> <P> The nondisease - carrying head louse differs from the related disease - carrying body louse (Pediculus humanus humanus) in preferring to attach eggs to scalp hair rather than to clothing . The two subspecies are morphologically almost identical, but do not normally interbreed, although they will do so in laboratory conditions . From genetic studies, they are thought to have diverged as subspecies about 30,000--110,000 years ago, when many humans began to wear a significant amount of clothing . A much more distantly related species of hair - clinging louse, the pubic or crab louse (Pthirus pubis), also infests humans . It is visually different from the other two species and is much closer in appearance to the lice which infest other primates . Lice infestation of any part of the body is known as pediculosis . </P>

Where do ticks lie in the food chain