#human louse

Around the House with the Human Louse

The human louse (Pediculus humanus) is a species of louse found worldwide. As parasites, they exclusively inhabit the hair of humans (Homo sapiens). The species is divided into two subspecies based on the part of the body in which they specialize; Pediculus humanus capitis, aka head lice, arefound on the head, while Pediculus humanus humanus, or cooties, only parasitize the body. Both species may also be found on human clothing, although P. h. humanus is more common than their head-exclusive counterpart.

Both subspecies are characterised by a small head, a bulbous abdomen, and legs which end in sharp claws suitable for clinging to hair. They are generally grey or pale yellow in color, although their abdomens may turn red when they feed. Head lice are usually smaller than body lice; the former only reaches 1-2 mm (0.03-0.07 in) in length, while the latter can reach up to 3.5 mm (0.13 in). In both species, the males are slightly smaller and have a more pointed abdomen and longer forelimbs.

Human lice feed exclusively on the blood of humans. Adults have specialized mouthparts which enable them to pierce the skin and draw blood. Individuals must feed at least once every other day, or starve to death. Because of their host specialization, P. humanus have no natural predators, although they are frequently removed by their hosts via natural and chemical means.

P. humanus have an extremely rapid reproductive cycle. After mating, females use a keritan-based glue to attach attach a number of eggs to their hosts' hair; head lice can lay 4-6 eggs a day for a total of 150 eggs over her lifetime, while cooties can lay up to 10 eggs a day adding up to 300 eggs over her life. The eggs, or 'nits', of both species hatch within a week, and immediately begin feeding on their host. Nymphs molt three times and reach full maturity within 2-3 weeks. Males die soon after mating, and females die within a month of their final molt.

Conservation status: P. humanus has not been evaluated by the IUCN. They are an extremely widespread species, and considered pests throughout their range.

Photos

Mohammed El Damir

CSIRO

Human Louse (Pediculus humanus)

Family: Human Louse Family (Pediculidae)

IUCN Conservation Status: Unassessed

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The Human Louse is a tiny (2-4mm long), wingless, parasitic insect that lives exclusively on the bodies of humans, and can be found almost everywhere that humans live. Two distinct subspecies exist, differentiated by where on a human they live: the Head Louse (Pediculus humanus capitis) lives, feeds and breeds on the scalp, while the Body Louse (Pediculus humanus humanus) lives and breeds inside clothing, and only moves onto its host’s body to feed. It feeds exclusively on human blood (which provides it with both the nutrients needed to live and the protein required to produce eggs) and must feed frequently to survive - if separated from a host and unable to feed a Human Louse will starve in 1-2 days. Human Lice are very short-lived (with a typical lifespan of around 30 days), but develop and reproduce at an astounding rate - their eggs hatch within 6-7 days of being laid, they reach full maturity at only around 10 days old, and after mating just once an adult female (which can be distinguished from males thanks to their slightly larger size) can lay 4-8 eggs every day for the rest of her life. Head Lice lay their eggs on strands of hair, while Body Lice lay their eggs on the fibers that make up clothing. Although they can cause itching and mild irritation, Human Lice are not dangerous and are not believed to spread disease, though if allowed to build up in large enough numbers they may cause some damage to the scalp and hair follicles. As they cannot fly like mosquitoes or jump like fleas, Human Lice spread between hosts as a result of direct contact with hair or clothing that they are already inhabiting. Although Human Lice (particularly Head Lice) are often though to be a sign of poor personal hygiene, there is no known link between personal hygiene and susceptibility to lice infestation - there is even evidence suggesting that Head Lice may prefer cleaner hair. 

Extra Fun Fact: It is thought that the Human Louse has existed for almost as long as humans have, with the species likely being descended from lice that inhabited the bodies of the ancestors of our species. Fittingly, the closest living relative of the Human Louse, the Chimpanzee Louse (Pediculus schaeffi) lives only on the bodies of the closest living relatives of humans, Bonobos and Common Chimpanzees.

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Human head louse, Pediculus humanus Photos 1-2: Female Photos 3-5: Male Photo 6: Egg - dead after anti-louse treatment