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Looking in Stubbs and Drake, I could not be sure from this photo. What makes you certain that it is this species?
Thanks for any pointers...I do not find many horseflies, apart from hundreds of Haematopota pluvialis, which ruin many a day bird ringing, locally!
My Flickr photos...
Lat/Lng: 51.23236, -0.3511
OS grid ref: TQ152494