 Louse ( plural : lice ) is the common name for members of the order Phthiraptera , which contains nearly 5 @,@ 000 species of wingless insect . Lice are obligate parasites , living externally on warm @-@ blooded hosts which include every species of bird and mammal , except for monotremes , pangolins , bats and cetaceans . Lice are vectors of diseases , such as typhus , trench fever , and epidemic typhus .
 everybody knows that lice are parasites that live on the body and feed on blood . Lice can cause itching and irritation and may be a sign of poor hygiene .
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