Lice

Woodcut of head lice

Fig 3. Head lice are brushed out of the hair in this woodcut from 1536. The text quotes Pliny the Elder, who says that lice occur in an invisible way of the human body.

Lice and crab louse

Lice

Lice form an insect order Anoplura, or sucking lice, that do not have close relations to other insects. Lice are bloodsuckers. They live in the fur of mammals but not all kinds of mammals. They only live on one family of predators, namely the Canidae.

Pediculus humanus is a species of louse that infects humans. It comprises two subspecies:

the head louse and the body louse. They only live on humans. Our lice lead a very discreet life. They are part of our special parasite fauna and for humans – as a species – it is natural to have lice. When most of us are free of lice from time to time, it is because we have chosen to fight them. Without active control we would all have lice.
The crab louse is another species of louse specifically related to humans. The pediculus humanus and the crab louse are easy to control. Treatments are available over the counter at pharmacies. When lice still migrate from one person to another, it is because it often takes too long before they are discovered