Head lice are tiny insects. They are about the size of a sesame seed (2–3 mm long). Their bodies are usually pale and gray, but color may vary. One lice is called a louse. Head lice feed on tiny amounts of blood from the scalp. They usually survive less than a day if not on a person's scalp. Lice lay and attach their eggs to hair close to the scalp. The eggs and their shell casings are called nits.