Tiny insects that live only on people's scalp and hair. They hatch from small eggs called nits that firmly attach to a person's hairs near the scalp and cannot be easily moved up or down the hair as can specks of dandruff. They look like grains of sand. Nits may be found throughout the hair but are most often located at the back of the scalp near the neck and behind the ears. The eggs hatch in 6-10 days, with new lice reaching adulthood about 2-3 weeks later. The lice live by biting and sucking blood from the scalp. Lice can survive 1-2 days away from the scalp. Until a person with head lice is treated he or she can transmit them to others.