If you ever had head lice as a child, don't feel too bad -- it's pretty common because these tiny (sesame seed-sized) wingless insects spread so easily in groups of people living or staying together in close quarters [source: U.S. National Library of Medicine]. Lice eat not only blood, but also dead skin and body secretions. There are three different types of lice that infect humans: head lice, body lice and pubic lice (or crabs). Body lice and head lice have similar appearances, while pubic lice actually do have a crab-like appearance [source: CDC].
Lice attach themselves to their host's hair and affix their eggs to the hair with saliva, but their bites don't usually hurt or cause bumps. Lice infestations are called pediculosis [source: CDC]. Head lice spread through direct contact or sharing hairbrushes with an infected person. Body lice (which live in clothing) spread through shared clothing or towels. While pubic lice are often spread through sexual contact, they can also be transferred through shared clothing.
Diagnosing any type of lice requires careful examination of the hair, usually by using a special fine-toothed louse comb. Once the eggs hatch, it is easy to spot the empty shells (or nits) as they are white or whitish-yellow and are hard to remove from the hair. You may also see tiny black louse feces in the hair or on pillows. As with fleas and ticks, itching is caused by sensitivity to the bug's saliva, and it can be bad enough to keep you awake at night.
It can take awhile to be completely rid of the lice and nits. Usually you have to combine several different types of treatment options and repeat them two or three times. These include treating the scalp with a chemical pediculide such as pyrethrin. Combing through conditioner or oil-coated hair and flushing any lice or eggs caught clinging to the comb is also helpful. Some people have used things like gasoline, kerosene vinegar or hair bleach to get rid of lice, but these home remedies aren't effective (and, in the case of gasoline or kerosene, can be dangerous). You can also treat body and pubic lice with pyrethrin or other chemical insecticides. All clothes and linens must be washed in hot water.
Can you fill in the blank in this phrase: "Good night, sleep tight, don't let the ____ bite"? Learn about another external skin parasite next.