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Yellowjacket Mimic - Temnostoma alternans - female

Yellowjacket Mimic - Temnostoma alternans - Female
Harvard, Worcester County, Massachusetts, USA
June 17, 2005
Size: about 20mm
I thought this was a queen jellowjacket. It was the same size, but appeared just a little darker than it should be for a yellowjacket, and the wings are brown. Any ideas what this might be?

Thanks Tony

per Richard's remark placing this in the vespiforme group, and seeing an identical looking fly in Marshall's book (1) labelled T. vespiforme.

The 2 yellow spots
on the top of the thorax suggests this is T. alternans, Fig 7 in Marshall's book (p.470) and not vespiforme

Maybe the best Yellowjacket mimic.
Temnostoma species of the rightly named "Vespiforme" group are probably the best existing imitators of Yellowjacket queens in the current Dipteran fauna. Indeed, telling them apart in flight is virtually impossible, even from very close. Also the humming sound is alike, contrary to many other hoverflies whose "buzz" is clearly higher-ptiched than that of an average wasp-queen.
The black, specialized forelegs are held just like the antennae of a true wasp, and even on the ground, the fly often moves them in the same way a yellowjacket does with its antennae.
Other Temnostoma pictures of this guide shows species of the "Bombylans" group, i.e. darker, more slender species which rather mimic solitary wasps, as Mr. Eaton states.

Moved to guide
Nice shot! It is different enough from the other two images of Temnostoma in the quide that it must be a different species in that genus.
Moved to guide. It is a female.

Syrphid, genus Temnostoma!
Hello Tom,
It is a mimic indeed, and it belongs to the Syrphids. This female is in the genus Temnostoma, of which there are 10 species in the Nearctic. Interesting is that these flies use their first pair of legs like a kind of pseudo-antennae, and they wave with them like a wasp would do with its antennae!
Gerard Pennards

Thanks Gerard, I thought it might be a fly, but had no idea what kind.

looks like
a fly, diptera, to us. One pair of wings and the face of a fly!

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