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Syrphus sp.

Syrphus sp.
Haydenville, Hampshire County, Massachusetts, USA
October 22, 2011
My tentative I.D. (Eupeodes americanus) is based only on browsing through the Syrphidae here at Bugguide. E. americanus seems to be a common species, so it's probably a good guess, and this one sure looks like some of the other photos of this species, but I have no idea what the actual diagnostic features might be (short of a line down the front of the face). Have I stumbled across a correct identification?

Images of this individual: tag all
Syrphus sp. Syrphus sp.

Moved from Syrphini.

Moved from Syrphid Flies.

Eupeodes does not have the ye
Eupeodes does not have the yellow markings overlap the continuous black edging of the abdomen.
Confident to Syrphini..

Moved from ID Request.

Beautiful picture! I love how I can see your head and the treeline in the reflection on its thorax! It looks like Syrphus to me, or maybe Epistrophe. Eupeodes americanus has a black (marginated) rim around the abdomen. In this picture it looks like the yellow stripes continue uninterrupted to the ventral side.

Thank you, Eleanor. The photo of E. americanus that looked so similar to my untrained eye is number 522715, but I see what you mean about the rim around the abdomen. I've uploaded a second photo of the same individual, and indeed, there is no rim on this one. The insects look so similar (to my still only slightly less untrained eye) that it's hard to believe they're in different genera, but that's mimicry for you, I guess. Do you know if there's a particular species of wasp that they mimic?

No, I don't know what species. I'm not sure they actually have a known model...maybe they are loose mimics of yallowjackets. I know what you mean about almost-identical genera! I collected thousands of syrphids for my masters and it took a lot of peering through microscopes and keying-out to discern those Syrphini!

But why mimic another syrphid?
It does seem that just having a bright yellow and black striped abdomen should offer some protection against predators familiar with yellowjackets--anything to make your predator hesitate for a moment must help. Why, though, would two non-stinging insects from different genera resemble each other this closely? It's a little hard to believe that these two species are noxious and are distinguishing themselves, as Mullerian mimics, from other more palatable Syrphini.

I suppose it's possible that the resemblance is coincidental. There probably are developmental limitations on the type of pattern that can occur on an abdomen, and when it comes time to find a mate, they probably think they look nothing at all alike, so there would no disadvantage to stumbling upon a very similar pattern by chance. But if they are mimics of each other, it does kinda make me wonder why.

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