The Collaborative International Dictionary of English v.0.48:

Tsetse \Tset"se\, n. (Zool.)
   A venomous two-winged African fly (Glossina morsitans)
   whose bite is very poisonous, and even fatal, to horses and
   cattle, but harmless to men. It renders extensive districts
   in which it abounds uninhabitable during certain seasons of
   the year. [Written also tzetze, and tsetze.]
   [1913 Webster]