The life cycle of lice have 3 distinct stages: egg, nymph and adult.
Lice Eggs (Nits)
Lice eggs are called nits (hence the term, nit picking). The are small (0.8mm by 0.3mm), oval shaped and ussually a yellowish white. Their small size makes them hard to see, and many times they are confused for dandruff.
When the nits are laid by the female louse they are ‘cemented’ to the base of a shaft of hair. This securely holds the egg in place. Nits are usually found attached within 6mm of the scalp.
The nits take about a week to hatch (between 6 and 9 days).
Nymphs
When a nit hatches it releases a nymph. The remaining egg shell becomes easier to see as it turns a dull yellow. It still remains attached to the hair shaft.
Nymphs look very similar to adult lice, just smaller. They are about the size of a pinhead.
Over a 7 day period after hatching the nymphs will mature and molt 3 times, after which time they are considered adults.
Adults
An adult louse is about the same size as a sesame seed. Each of their 6 legs has claws that are specialty adapted to grab and hold hairs. Adult lice will be a tan to grayish-white color. Interestingly, in individuals with darker hair, the adult louse will appear darker. Female lice tend to be larger then the males and can lay up to 8 nits a day.
Adult lice live for up to 30 days.
Information Source: US Center for Disease Control (CDC)
Having lice problems? Check out our handy guide to get rid of lice.