Late-flying Episyrphus often have this dark abdomen. Two of three seen today were like this.
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I was going to ask about a jet-black one of these seen today, which you've just explained.
It was impressive, but eluded me. As did a little orange Didea (bah!) and a dark little Chalcosyphus type (humph!). These two seemed to have emerged from the Ivy at it's thickest point, decided it was too cold and gone back in. Nice view of the Didea floating close in among the leaves, quite different it seemed to me from Eupeodes or Syrphus
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Lat/Lng: 53.8, -0.9
OS grid ref: SE7844