New Hoverfly species -Syrphus ribesii

I found a lone Hogweed which was a Hoverfly party, particularly for five or six specimens that turned out to be Syrphus ribesii. I always start optimistically when trying to ID hoverflies because the field guide by Ball and Morris is so helpful. I try and make sure that my photos include face, legs and eyes as well as the thorax patterns and importantly the wing veination so I take quite a few in the hope I have all the info I need. This particular hoverfly is difficult to separate from S. torvus and S. vitripennis but I got lucky that my main photos were of a female (determined by the gap between the eyes) and that I had a good focus on the femur (which is black only at the top in the female S. ribesii). It turns out that this nails the specimen as being ribesii rather than one of the others.