Mydas Fly

I thought I’d snuck a photo of a wasp (most wasps are not tolerant enough to let my camera get close) until I got the photos home and had a better look. This 35mm long insect is a wasp mimic — a clever fly which makes its living by looking like something much pointier and more dangerous than it actually is.

Nearly every member of the family Mydidae (Mydas flies) mimics a species of wasp. Mydid flies are all big, sturdy flies with very wasp-like wings, but the giveaway that they are not wasps is the tubular (instead of teardrop-shaped) abdomen, and the short, blunt, “clubbed” antennae. (There are other differences, but those are the most immediately obvious.) Mydas maculiventris is pretending to be a Polistes paper wasp, similar to this one.

Mydas flies do not sting, and most do not even bite. Some (including M. maculiventris) are beneficial predators, eating the “white grub” beetle larva pests which infest human lawns; many drink nectar and work as pollinators. It is actually pretty rare to see one; the adults have a relatively short lifespan.

This individual is male; a female would have a pointier abdomen.

Here’s another individual photographed with different equipment almost a year later; I think I’ve improved a bit:

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