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Very much a fly of the early spring...I have not heard of it having an autumn generation at all. It has wholly black legs, as well. Bibio pomonae is the large late summer species.
My Flickr photos...
I was quite surprised to find 4 of these in my moth trap this morning.
I think you would expect them, given the location. I had one in a moth trap in the Vale of York a few years ago...an unusual record for what is very strongly an upland fly. There may be a population on the Wolds, though, I suspect.
Lat/Lng: 54.2, -2.1
OS grid ref: SD9788