Head lice and nits (eggs) are parasites that have plagued humans for thousands of years. They are spread easily from person to person and are a major nuisance, causing itching and an uncomfortable crawling sensation on the scalp. There a several signs to look for when checking for lice.
Nits are the eggs of lice, and are usually white, off-white or clear. They are small and oval-shaped. They are usually close to the scalp, about 1/2 to 1/4 inch into the hair shaft. They are difficult to see, and are sometimes mistaken for dandruff. However, if you try to pick it off, they don't come out of the hair as easily as dandruff.
Head lice are usually brown, and larger than the nits. They have elongated bodies, six legs, and are about the size of a sesame seed. They have no wings. They can be difficult to detect in dark hair, but they'll likely be moving, which makes them easier to spot. They can be treated with over the counter medications and a lice comb. Be sure to remove the nits as well, or they can hatch and create a new infestation.