I've just found a male Neria that I'd identified as N.cibaria, probably on the basis of the colour of the upper frons, i.e. orange right up to the anterior ocellus, BUT with the post abdomen of N.commutata. I've trawled internet images (though I know they can be unreliable) and find the upper frons is shown as velvety black in this species (as described in Darwyn's key).
The female below (the only Neria I've kept this year) has an all-orange frons, but an almost entirely black ovipositor sheath - just a narrow brown rim near the articulation with tergite 6. There are scattered pale hairs on it, but no row of long hairs. This fly came from calcareous fen at Hockley Meadows near Winchester, in June 2020.
Is it, perhaps, that I'm misunderstanding the characters?
