On Marsh Marigold in urban park pond, Bristol
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Thanks Ian. Having gone back to Stubbs and Falk, I'm sure you are right about the genus. It isn't Dasysyrphus. It's a female Melangyna sp. But I wish I had had my net with me. I'll have to wait until next spring now to get a specimen - and if I get one, it might still not be the species this particulat individual is.
Lat/Lng: 51.4743, -2.5874
OS grid ref: ST592752