The Collaborative International Dictionary of English v.0.48:

Eristalis \E*ris"ta*lis\, n. [NL.] (Zo["o]l.)
   A genus of dipterous insects whose young (called rat-tailed
   larv[ae]) are remarkable for their long tapering tail, which
   spiracles at the tip, and for their ability to live in very
   impure and salt waters; -- also called drone fly. Eristic