General ID

Earlier in the year, our garden pond in Peterborough (Cambs, but VC32) was notable for a couple of things. Firstly, it seemed riddled with caddisfly larvae, making their little capsules from the fist leaves of duck weed gathered from the surface and keepign the surface nice and weed free. Secondly, there seemed to be loads of weird grey, segmented leech-like creatures, which judging from the way they were making little circular depressions in the surface tension were breathing air like insect larvae. But they were insect larvae the like of which I hadn't seen before. I tried looking them up using Google and occasionally had hints they may be soldier fly larvae.

At the weekend, Eddie spotted an impressively large yellow and black fly near the edge of the pond. We saw similar flies last year round the pond and I have seen one or two this year to. This one was very passive and ripe for photography:

I am confident that this is a Stratiomys soldier fly and it is between Stratiomys potamida, the Banded General, and S. chamaeleon, the Clubebd General. I suspect the former, but await some ID advice. At the moment I am not sure how to tell the two generals apart...

Update: I have had some advice on general ID. This one is S. potamida. The other species has an angled mark on the scutellum and broader yellow bands (and is v rare); so that makes sense.