eristalis

from The Century Dictionary.

• noun A remarkable genus of flies, typical of the subfamily Eristalinæ, having the marginal cell closed and petiolate, the thorax without any yellow markings, and the front evenly arched.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Zoöl.) A genus of dipterous insects whose young (called rat-tailed larvæ) 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.