Lice in the context of "Parasitism"

Parasitism is a close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson characterised parasites' way of feeding as "predators that eat prey in units of less than one". Parasites include single-celled protozoans such as the agents of malaria, sleeping sickness, and amoebic dysentery; animals such as hookworms, lice, mosquitoes, and vampire bats; fungi such as honey fungus and the agents of ringworm; and plants such as mistletoe, dodder, and the broomrapes.

There are six major parasitic strategies of exploitation of animal hosts, namely parasitic castration, directly transmitted parasitism (by contact), trophically-transmitted parasitism (by being eaten), vector-transmitted parasitism, parasitoidism, and micropredation. One major axis of classification concerns invasiveness: an endoparasite lives inside the host's body; an ectoparasite lives outside, on the host's surface.

The head louse (Pediculus humanus capitis) is an obligate ectoparasite of humans. Head lice are wingless insects that spend their entire lives on the human scalp and feed exclusively on human blood. Humans are the only known hosts of this specific parasite, while chimpanzees and bonobos host a closely related species, Pediculus schaeffi. Other species of lice infest most orders of mammals and all orders of birds.

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.

Biting is an action involving a set of teeth closing down on an object. It is a common zoological behavior, being found in toothed animals such as mammals, reptiles, amphibians, fishes, and arthropods. Biting is also an action humans participate in, most commonly when chewing food. Myocytic contraction of the muscles of mastication is responsible for generating the force that initiates the preparatory jaw abduction (opening), then rapidly adducts (closes) the jaw and moves the top and bottom teeth towards each other, resulting in the forceful action of a bite. Biting is one of the main functions in the lives of larger organisms, providing them the ability to forage, hunt, eat, build, play, fight, protect, and much more. Biting may be a form of physical aggression due to predatory or territorial intentions. In animals, biting can also be a normal activity, being used for eating, scratching, carrying objects, preparing food for young, removing ectoparasites or irritating foreign objects, and social grooming. Humans can have the tendency to bite each other whether they are children or adults.

Bites often result in serious puncture wounds, avulsion injuries, fractures, hemorrhages, infections, envenomation, and death. In modern human societies, dog bites are the most common type of bite, with children being the most common victims and faces being the most common target. Some other species that may bite humans include urban animals such as feral cats, spiders, and snakes. Other common bites to humans are inflicted by hematophagous insects and arthropods, such as mosquitoes, fleas, lice, bedbugs, and ticks (whose "bites" are actually a form of stinging rather than true biting).