Bumble Bee Mimic Robber Fly

I met this Bumble Bee Mimic Robber Fly almost 2 months ago at Round Valley. The common name is a mouthful, but really does convey a lot of information about these insects:

  1. Bumble Bee Mimic: They have evolved to look like bumble bees. This gives them 2 benefits. First, some predators leave them alone for fear of getting stung even though these guys have no stinger. And second, they tend to prey on bees and beetles, and those insects might not recognize them as a predator (until it's too late).
  2. Robber Fly: Robber Flies are true flies that mainly prey on other arthropods.

I was initially suspicious that this wasn't a bumble bee because the wings looked wrong. They were thinner/longer than I'd expect, and there are only 2 wings. Generally speaking, if you see 4 wings (or 2 wings and 2 elytra) it's not a true fly. Seeing 2 wings ruled out a bumble bee (or anything else in the wasp/bee group of insects).

Somewhat similar to the odonates (dragonflies and damselflies) these guys will catch prey in flight. Some robber flies will even prey on odonates, though I suspect they're careful to attack one small enough for them to handle.

May 20, 2021 at the Round Valley Reservoir
Photo 132040260, (c) jpviolette, some rights reserved (CC BY-NC)


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