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It is a male Beris. The description of B. morrisii by Steven Falk "rather long, pale yellow legs and relatively clear wings that have a yellowish base, thorax rather bright metallic green. Males have pale hairs on top of the thorax" (https://www.flick...905398599/) seems to fit quite well, as there are clearly no black hairs. The key http://www.brc.ac...014_v2.pdf is less helpful, as we cannot decide whether the abdomen is orange (with or without crossbands) or black. B. morrisii has a black abdomen, but your fly may well have one, too. So I vote for B. morrisii!