1. Any one of numerous species of small, wingless, suctorial, parasitic insects belonging to a tribe (Pediculina), now usually regarded as degraded hemiptera. To this group belong of the lice of man and other mammals; as, the head louse of man (pediculus capitis), the body louse (P. Vestimenti), and the crab louse (Phthirius pubis), and many others. See crab louse, dog louse, cattle louse, etc, under crab, dog, etc.
2. Any one of numerous small mandibulate insects, mostly parasitic on birds, and feeding on the feathers. They are known as mallophaga, or bird lice, though some occur on the hair of mammals. They are usually regarded as degraded pseudoneuroptera. See mallophaga.
(Science: zoology) louse fly, any one of numerous species of mites which infest mammals and birds, clinging to the hair and feathers like lice. They belong to Myobia, Dermaleichus, Mycoptes, and several other genera.