Stages of Lice
Head lice grow in three stages and are acquired from other infested people when the lice are in the adult stage. Nits are the first stage, and they are actually lice eggs found firmly attached at the base of a hair. Only those eggs deposited by an inseminated female will hatch. Once the lice emerge from their eggs after incubation, they are considered nymphs and are sexually immature, so they are unable to reproduce with other adults or nymphs. When nymphs mature into adult lice, they can start to mate.
Lice Egg Cycle
After mating and consuming a blood meal, the female will gestate for 1 to 2 days and will then lay her eggs where the hair is connected to the scalp. In a little over a week, the nits will hatch, allowing the newly formed nymph to emerge. After another 10 days, the nymphs will have matured into adult lice and begin to feed, grow, and develop until it attains the adult stage about 9 to 12 days after hatching. Once matured, it will be capable of mating with females, who can lay up to 8 nits a day.
Lice Life Cycle
Once lice are fully matured into adults, they are physically characterized by their tan to grayish-white color and are about 2 millimeters. Adult lice derive nutrients by blood-feeding once or more often each day, and cannot survive for more than one day at room temperature without steady access to a person's blood. From gestation to adulthood, lice can remain on the human scalp as nits and nymphs for around 20 days, and as mature adults up to an additional 30 days.