The life cycle of lice

There are 3 species of lice that live on humans:

  • Head lice
  • Body lice
  • Aphid

Because head lice and crabs are very closely related, we have chosen to combine the description of their life cycle in one section. The life cycle of crabs has its own separate section.

Lice have a life cycle consisting of 3 stages: egg, nymph and adult

The lice life cycle is divided into 3 stages: Egg, nymph and adult. The nymph stage is divided into 3 sub-stages. The illustration above is based on body lice, but head lice have the same cycle.


Note that both head lice, body lice and crabs need to consume blood in all stages (except the egg stage) to survive and continue their development. All adult lice can live for up to 30 days.


Head lice and body lice

It is believed that the body louse evolved from the head louse when humans started wearing clothes. This is why the two species are so closely related. Their life cycle is almost identical and goes like this:

  • Egg stage: The head louse lays its eggs in head hair, while the body louse lays its eggs in clothing seams. A female louse lays 3-7 eggs per day. After 6 - 11 days, the eggs hatch (11 days for head lice and 6 - 9 days for body lice).
  • Newborn diet: After hatching, nymphs must ingest blood from their host within 24 hours. If they fail to do so, they die. The nymphal stage consists of three sub-stages that last a total of 6 days in head lice and 10-12 days in body lice.
  • Adult stage: The adult lice feed exclusively on human blood and can live in up to 40 days. Males and females mate, after which the females lay eggs, completing the life cycle.

Head lice and crabs can develop from eggs to adult lice in 15 - 23 days. Their total life span can be up to 63 days.

Read more about head lice here and body lice here.



Crabs differ from head lice and body lice in several ways; they are smaller, have more rounded bodies and live primarily in pubic hair. Their life cycle goes like this:

  • Egg stage: The adult female aphid lays about 3 eggs per day. She lays her eggs in the dense hair around the genitals, but sometimes also in other dense body hair such as beards or eyelashes. The eggs hatch after 6-10 days.
  • Newborn diet: After hatching, three nymph stages follow with a total duration of 27 - 33 days. The first nymphal stage lasts 5-6 days, the second 9-10 days and the third 13-17 days. The nymphal stages end when the adult stage begins.
  • Adult stageAdult crabs usually live between 15 and 25 days, but can live for up to 30 days. Their diet consists entirely of human blood. They ingest blood 4-5 times a day. Males and females mate, after which the females lay eggs to complete the cycle.

A crab develops from egg to adult in 33 - 43 days. Adult crabs can live for up to 30 days, so the total life cycle can last up to approximately 55 days.

Read more. more about crabs here.