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I watched this Siphona feeding on ivy nectar yesterday. I know there's not much chance of determining the species from photos, but thought I'd ask whether there are any external characters I should try to capture if I get another chance. Or is it all down to the 'private parts'?

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Looks female to me, which makes it even more difficult to say what it is ;) If I were to guess then I would say Siphona geniculata, just because it looks like it has T1+2 bristles and it has that dull brown colour and it is the commonest species in England :)

Features that would be useful are a good lateral head shot (ratio of frons, face & antenna in important); dorsal of thorax & abdomen showing bristles clearly ... and just be lucky - you might find one that is identifiable ;)

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Thanks Chris, I thought it was likely to be geniculata. Perhaps they should have called the species S. cf geniculata to save time:P

Thanks for the tips - I'll keep trying:)

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I sorry to disagree

The parafacialia seem to be very narrow (for geniculata).
Moreover, the frons is short, the third antennal segment long and the setae on tergites have strong black spots.

So S. setosa (also with marginals on T1&2) comes in mind.

Theo

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Thanks Theo! That makes it even more interesting for me, especially as the gallery has pinned specimens of both species and I can try to see the differences.

Stephen.