The Collaborative International Dictionary of English v.0.48:

Rubytail \Ru"by*tail`\, n. (Zool.)
   A European gold wasp (Chrysis ignita) which has the under
   side of the abdomen bright red, and the other parts deep
   bluish green with a metallic luster. The larva is parasitic
   in the nests of other wasps and of bees.
   [1913 Webster]