Narrow-winged Horsefly Tabanus maculicornis

Steven Falk's Flickr photos really helped me out here. The fly was found on the inside of my patio doors and I initially attempted to key it using Stubbs & Drake. I felt the alula was slightly wider than shown for maculicornis and although the pattern on the tergites was similar to that shown for maculicornis, it wasn't very clear-cut so I continued through the key past maculicornis. I reached a choice between miki (very unlikely) and bromius, but although the single band through the eye supported an ID of bromius (and for what it's worth, which isn't much, ObsIdentify was 100% sure it was bromius) but I was troubled by the presence of black hairs in the corner of tergite 2 which was supposed to be a feature of miki rather than bromius. Admittedly there were yellow hairs here too, but this was enough to make me want to investigate it a bit further and I turned to Steven Falk's Flickr albums. Looking at one of his photos of Tabanus bromius it was immediately obvious that the alula on that species is in fact much wider than shown on my specimen, so I looked up his photos of Tabanus maculicornis. Not only was the alula closer to mine (though a bit narrower - more exactly matching the diagram in Stubbs & Drake than mine did) but it was also similar to mine in terms of the pattern of the tergites.

female Narrow-winged Horsefly Tabanus maculicornis showing face, left alula, right wing. corner of tergite 2, tergites (right wing removed) and sternites, North Elmham (Norfolk, UK), 26th June 2025