The louse clinging to hair. Its dark stomach indicates a recent feed of bloodAnyway, despite my dread of live lice, they are fascinating creatures on their own right. Lice are apterous bloodsucking insects (order Phthiraptera) that are adapted to clinging to hair - hence, they are found only in mammals. They lay their eggs gluing them in a shaft to individual hairs, close to the scalp. The newborn lice are nymphs, they are smaller and simpler than adults and metamorphose slowly into adults in three stages. Individuals live for a month or so and females can lay several hundreds of eggs in their lifetime. The study of such species-specific ectoparasites can provide information on the evolution of their hosts. Humans are the host of two species of lice (wingless insects of the order Anoplura), the pubic louse and the hair/body lice complex. In the past hair and body lice were thought to belong to different species, one adapted to lay their eggs on hair, the other on clothing. It was thought that body lice had evolved with the invention of clothing into a separate species. Molecular analysis have revealed, though that the body louse has evolved several times and that they do not form a monophyletic unit separate from head lice. These studies have revealed more intriguingly that there are three old genetic lineages of lice (only one of them includes body lice) and the authors hypothesized that one of such lineages might have evolved in Homo erectus, and been transferred to modern humans when they met. A fascinating hypothesis that has proven to be difficult to test due to the lack of good calibrations for lice DNA.