These images are of the same insect
No interactions present.
Yes, it is the front and mid tarsi which are pale in pertinax, so it is not that species.
The dark, hairy-fringed and slightly swollen appearance of the hind tibiae of tenax is a good back up criterion, here.
Most Eristalis species have the dark facial stripe, including pertinax, but in tenax it is particularly broad. I'm not sure that really shows up here.
The large size and broad abdomen are useful features.
Be aware that in a few weeks, more species of Eristalis will be around, and then it all gets far more complicated!
My Flickr photos...
Thanks for the tips, I find these hoverflies rather taxing now but looking forward to the challenge.
Chris Brooks - www.dragonfly-images.co.uk
My Flickr site - www.flickr.com/photos/ceb1298
The ones i found were looking for an over winter spot. Other end of the season.
Lat/Lng: 51.2, -1.0
OS grid ref: SU7451