Chrysogaster virescens or solstitialis

[JRsbugs]

Hi,

This is a first for me, but I can't tell which it is. Hoping Roger Morris will look, or I will have to put it on diptera.info, or maybe someone else knows the difference.

I'm guessing C. solstitialis.

31st July on Achillea.

Janet

[Geoff F]

Well according to the Stubbs keys:

The hair on top of the thorax is erect, not inclined at 45 degrees, and the scuttellum hair is short. Which points to C. solstitialis.

But what is the eye angle? Eyes meeting at 90 degrees or less means C. solstitialis while more than 90 degrees means C. virescens.

It is difficult to find a true angle from a photo but I don't think they are more than 90 degrees (give or take a couple of degrees).

[JRsbugs]

Thanks Geoff, one day I will have to get that book! I have a few others which need identifying, finding which genus for a start can be challenging enough.

The eyes are less than 90 degrees, and yes the hairs stand on end so C. solstitialis it is.

[Geoff F]

But sometimes even that book leaves me confused. Particularly when I haven't managed an ideal angle for a key which starts with 'the colour of hair on the hind femur' etc.

I still can't decide on this Rhingia Pale Rhingia campestris or R. rostrata? and all the real experts on the Hoverfly Recording Scheme appear to be busy with their own efforts at the moment.

[Jason Green]

Evening all,

I'll go with solstitialis too - though the further North you go the more frequent virescens becomes. The antenna-base looks to be narrower than the gap between the inside-eye to outside-antenna space (here appearing to be a ratio of 1:1.12) which seems wider - another feature of virescens, but in females. It could be unreliable with males, or perspective from field-photographs.

I'll say C. solstitialis, but I had considered virescens (a nice head-shot by the way, Janet!).

Originally Posted by Geoff F

But sometimes even that book leaves me confused. Particularly when I haven't managed an ideal angle for a key which starts with 'the colour of hair on the hind femur' etc.

I know the feeling! Frustrating, I know. As distasteful as it seems to a lot, couplets like these are written assuming the reader has a specimen in hand - not a photograph, where all manner of things can make the perceived colour unreliable.

Take care,

Jason

[JRsbugs]

I got the female too!