? Xanthandrus...

Can you post a dorsal view, showing the spots on the abdomen? My 3 specimens, including 1 female have significantly darkened legs.

OK, but without removing a wing it's difficult to make the abdomen more visible. Also she's now lost her head in the endeavour.

Try Platycheirus fulviventris. This does not appear to be X. comtus, which only has small, distinctly circular yellow spots on tergite 2 and this appears to have more extensive yellow marks on T2. P. fulviventris has almost entrely yellow legs as well. Separating fulvivetris females from immarginatus and perpadillus can be difficult though.

I agree that this is not Xanthandrus.  The spots on tergite 2 are much larger than those on X. and are in nearly as big as those on tergites 3 and 4, except that they do not reach to the front or sides of the tergite.

However, which Platycheirus?  I agree that P. fulviventris is most likely.  The yellow legs are a giveaway, the only exceptions being the dull brown of the hind metatarsus AND the sharp black of the outside of the fifth hind tarsal segment.  Would you please check whether your specimens have this feature - I've not mentioned it here earlier, nor is it mentioned as diagnostic in any key.  P. immarginatus has (according to the revised key) dark markings on hind femur and/or tibia.

Thanks

Anthony