 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 . 
