Body Louse

• There are two forms: the head louse, which lives in the hair and is a nuisance without consequences, and the body louse, which lives in the seams of clothing and has been a vector of epidemic typhus, trench fever and relapsing fever, with devastating epidemics in wars and famines.
• Genetic study of the divergence between the two forms has been used to estimate when humans began to wear clothes, placing it tens of thousands of years ago.
• Its eggs, the nits, are cemented to the base of the hair with a substance that shampoo does not dissolve and that has to be removed mechanically with a fine-toothed comb.
• It has two subspecies, morphologically almost identical and able to interbreed: the head louse and the body louse. The difference lies in where they lay their eggs.
• Only the body subspecies transmits disease, and the diseases are serious: epidemic typhus, trench fever and relapsing fever.
• It neither jumps nor flies: it spreads by direct contact, and overcrowding favours its spread.
• Without feeding it dies within two or three days; a female lives about four weeks on the host.
• The direct harm of the infestation is trivial compared with that of the bacteria it carries.

Skeleton type

Invertebrate - chitin exoskeleton (insect)

Habitat and environment

Human hair and clothing

Size at birth

Nit of 0.8 by 0.3 mm, cemented to the base of the hair; the newly hatched nymph is the size of a pinhead

Sexual maturity

The nymphs go through three moults and become adults about 7 days after hatching

Gestation / incubation

The nits hatch in about 6 to 9 days; the full cycle from egg to adult takes 16 to 21 days

Litter / clutch size

Up to 8 nits a day and between 50 and 150 eggs over the female's lifetime

Sources consulted: Wikipedia (en): Pediculus humanus · CDC DPDx, ficha Pediculosis · Penn State Extension · Texas DSHS, ficha de piojos de la cabeza