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.
The non-disease-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. 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 morphologically different from the other two species and is much closer in appearance to the lice which infest other primates. Louse infestation of the body is known as pediculosis, pediculosis capitis for head lice, pediculosis corporis for body lice, and phthiriasis for pubic lice.
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OviparousOviparous animals are female animals that lay their eggs, with little or no other embryonic development within the mother. This is the reproductive...
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About 6–12 million people, mainly children, are treated annually for head lice in the United States alone. In the UK, it is estimated that two thirds of children will experience at least one case of head lice before leaving primary school. High levels of louse infestations have also been reported from all over the world, including Australia, Denmark, France, Ireland, Israel, and Sweden.
![Pediculus humanus var capitis AKA head louse; public domain from http://phil.cdc.gov/. [1] Content Provider(s): en:Centers for Disease Control and Prevention (CDC)/Dr. Dennis D. Juranek Now in Commons also.[1]--Gyllenhali 15:08, 28 December 2005 (UTC)](https://s3.animalia.bio/animals/photos/medium/original/pediculus-humanus-var-capitis.webp)
All stages except eggs are blood-feeders and bite the skin four to five times daily to feed. They inject saliva which contains an anticoagulant and suck blood. The digested blood is excreted as dark red frass.
Head lice reproduce sexually, and copulation is necessary for the female to produce fertile eggs. Parthenogenesis, the production of viable offspring by virgin females, does not occur in Pediculus humanus. Pairing can begin within the first 10 hours of adult life. After 24 hours, adult lice copulate frequently, with mating occurring during any period of the night or day. Mating attachment frequently lasts more than an hour. Young males can successfully pair with older females, and vice versa.
Experiments with P. h. humanus (body lice) emphasize the attendant hazards of lice copulation. A single young female confined with six or more males will die in a few days, having laid very few eggs. Similarly, death of a virgin female was reported after admitting a male to her confinement. The female laid only one egg after mating, and her entire body was tinged with red—a condition attributed to rupture of the alimentary canal during the sexual act. Old females frequently die following, if not during, copulation. During its lifespan of 4 weeks a female louse lays 50-150 eggs. Eggs hatch within 6–9 days, each nymphal stage last for 4–5 days and accordingly the period from egg to adults lasts for 18–24 days. Adult lice live for an additional 3–4 weeks.
