The Collaborative International Dictionary of English v.0.48:

Tachina \Tach"i*na\, n.; pl. Tachinae. [NL., fr. Gr.
   tachino`s, for tachy`s swift.] (Zool.)
   Any one of numerous species of Diptera belonging to Tachina
   and allied genera. Their larvae are external parasites of
   other insects.
   [1913 Webster]