Head louse Totally Explained

Everything about Head Lice totally explained

The head louse (Pediculus humanus capitis) is an obligate ectoparasite of humans. Head lice are wingless insects spending their entire life on human scalp and feeding exclusively on human blood. Lice infestation is known as pediculosis.
The head louse (and lice in general) differ from other hematophagic ectoparasites such as the flea in that lice spend their entire life cycle on a host. Head lice can't fly, and their short stumpy legs render them quite incapable of jumping, or even walking efficiently on flat surfaces. The thoracic segments are fused, but otherwise distinct from the head and abdomen, the latter being composed of seven visible segments. Head lice are grey in general, but their precise color varies according to the environment in which they were raised. Eggs are generally laid within 1 cm of the scalp surface. After hatching, the louse nymph leaves behind its egg shell, still attached to the hair shaft.

Nits

egg or a louse nymph. With respect to eggs, this rather broad definition includes the following:

Viable eggs that will eventually hatch
Remnants of already-hatched eggs
Nonviable eggs (dead embryo) that will never hatch

This has produced some confusion in, for example, school policy (see The "no-nit" policy) because, of the three items listed above, only eggs containing viable embryos have the potential to infest or re-infest a host. Some authors have reacted to this confusion by restricting the definition of nit to describe only a hatched egg:
Lice are also important in the field of Archaeogenetics. Because most "modern" human diseases have in fact recently jumped from animals into humans through close agricultural contact, and also given fact that Neolithic human populations were too scattered to support contagious "crowd" diseases, lice (along with such parasites as intestinal tapeworms) are considered to be one of the few ancestral disease infestations of humans and other hominids. As such, analysis of mitochondrial lice DNA has been used to map early human and archaic human migrations and living conditions. Because lice can only survive for a few hours or days without a human host, and because lice species are so specific to certain species or areas of the body, the evolutionary history of lice reveals much about human history. It has been demonstrated, for example, that some varieties of human lice went through a population bottleneck about 100,000 years ago (supporting the Single origin hypothesis), and also that hominid lice lineages diverged around 1.18 million years ago (probably infesting Homo erectus) before re-uniting around 100,000 years ago. This recent merging seems to argue against the Multi-regional origin of modern human evolution and argues instead for a close proximity replacement of archaic humans by a migration of anatomically modern humans, either through inter-breeding, fighting, or being more fit to use available resources.
Analysis of the DNA of lice found on Peruvian mummies have led to some surprising findings. The research indicates that some diseases (like typhus) may have passed from the New World to the Old World, instead of the other way around.

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