Bernd Heinrich, Summer World: A Season of Bounty
(New York: Ecco, 2009), pp. 185-186:
Lice are ectoparasites (parasites living on our skin rather than under it), and
ectoparasites are remarkably species-specific; each kind of bird or mammal has
its very own louse and flea species living on it because each is an island with
regard to the others.
However, even though any one nonhuman mammal species has the dubious honor of hosting only one of each louse or flea species, humans are unique: we have three species of lice. They are head lice (Pediculus humanus capitis); body lice (Pediculus humanus corporis), which live primarily in clothing; and pubic lice (Pthirus pubis).