Lice are wingless ectoparasites. There are two main kinds of lice in the order Phthiraptera. These are the biting lice, which are most often found on birds, and the sucking lice, which are found on mammals. The scientific name of the order comes from the Greek phtheir (louse) and aptera (wingless).

One of the best known lice is Pediculus humanus - the human louse - which has two distinct races. The race capitis may be found in the hair on the head, and their eggs, stuck to hairs, are termed nits. These can be very difficult and time consuming to remove - this is where the term 'nit-picking' came from.

The race corporis is found on the body. Body lice can carry diseases such as relapsing fever (caused by Borellia recurrentis) and typhus (Rickettsia prowazeki) although only if they feed on someone who already has the disease. Sucking lice on domestic animals can also spread disease.

A photograph of the human head louse _Pediculus humanus_.

The human head louse (Pediculus humanus) is commonly known as a nit.
CDC/Dr. Dennis D. Juranek

Other names for (or types of) Phthiraptera include:

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