- Head lice are small insects – about the size of a sesame seed when fully grown – that live in the hair and on the scalp of humans. They vary in colour from light to dark brown and sometimes appear reddish after a blood meal.
- Head lice have claws on the end of each their six legs that enable them to cling to the hair and move about. They cannot jump and do not have wings, so they cannot fly.
- Head lice breathe through holes in the side of their bodies called spiracles. When the hair is wet, e.g. during shampooing, these spiracles can close to stop the louse from drowning.
- Head lice feed on blood from the scalp. They have a specially designed mouth that pierces the skin and injects saliva to stop the blood from clotting, and then they suck up the blood/saliva mixture. This saliva can be a cause of the itching sometimes experienced.
- Head lice cannot survive for long away from a human head, since they quickly dehydrate and die without their blood meals.
A female head louse only needs to mate once to be able to lay fertilised eggs for the rest of her short life.