"Look for a slight but distinctive wing shade on E. horticola and E. intricarius which could be mistaken for Merodon equestris."
Also in Eristalis intricaria (sorry but I'm used to 'a' instead of 'us') the hind tibia has a pale section where Merodon equestris doesn't (if they are the only legs you can see). E. intricaria can also have some, or a lot of orange hairs on the thorax, I have had some in the past but don't have pics on this computer.
The wing shading can also be on E. pertinax so other features should be looked at for E. horticola, in particular male front leg femur with long yellow hairs, male and female hind femur "basal half yellow bicolor".
The Canadian key gives for E. rupium the stigma being more than 3.5x as long as it is wide (French site says 2x), and brown to black flagellum.
Now all we need to do is combine the two keys for the ones present on both
I have two pics of Eristalis intricaria taken on 22nd April 2009 and 25th August 2009. I have pics from last year taken in July.
