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The Collaborative International Dictionary
Eristalis tenax

Drone fly \Drone" fly`\ (Zo["o]l.) A dipterous insect ( Eristalis tenax), resembling the drone bee. See Eristalis.

Wikipedia
Eristalis tenax

Eristalis tenax is a European hoverfly, also known as the drone fly (or "dronefly"). It has been introduced into North America and is widely established.