Head lice are tiny, wingless insects that live on the human scalp (clean heads usually). They are about as big as sesame seeds. Head lice sustain themselves by sucking blood - just as mosquitoes do. However, unlike mosquitoes, lice cannot fly or jump from one person to another; they can only crawl. Children often get head lice from head-to-head contact with other children, but may also get them by sharing personal items such as hats, combs, or headbands.