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
Gilles San Martin
