The Life Cycle of Head Lice

Knowing the life cycle of head lice will help you to treat you and your family.

The first stage is the egg. Commonly called nits, head lice eggs are tiny and yellowish white. They are attached to the hair at an angle close to the scalp. They need to be near the scalp because body heat and humidity are necessary for successful incubation before they hatch. After the lice have hatched the empty nit casings can stay attached to the hair for months so strong is the louse "glue".

Incubation takes 7 to 10 days and the newly hatched lice (or nymphs as young lice are called) are virtually transparent. This makes them incredibly difficult to spot. As they begin to feed on human blood they began to develop a reddish brown colouration.

The nymphs moult three times as they grow before becoming fully matured adults. From hatching to adult form takes 7 to 10 days. Once adult the females can start laying eggs. The female louse only needs to mate once as she stores spare sperm in her body for future use.

An adult head louse can live from twenty to thirty days on a host and during this time the average female will lay up to a hundred eggs. They feed on blood every 3 to 4 hours.

If they fall off their human host hair (which they rarely do) they can live up to 48 hours before dying. As they are very specialised once away from hair head lice find it hard to reattach themselves.

The nits are particularly resilient and resistant to whatever is thrown at them. It's this that makes repeat treatments important. Your initial treatment may have killed the lice but you'll still have eggs waiting to hatch. Timed correctly your next treatment will kill newly emerged lice before they have a chance to mature and lay their own eggs.