Head lice are tiny, wingless insects that live on the human scalp. They are about as big as sesame seeds. Lice eggs are about the size of poppy seeds and are difficult to see because their color easily blends in with the infested child's hair. Eggs are laid near the root of the hair and are attached with a waterproof, glue-like substance that can't be washed or blown away.
Once lice have hatched from eggs, they leave empty eggshells behind called "nits". Nits vary in color—from yellowish-brown to white.
We have illustrations and details in the section called How to Recognize Lice on this site.