I've watched these small flies, buzzing around just above the water's surface, over several seasons, but never been able to get a good enough shot to identify what they are. In the past I've tried using a very high ISO and a very fast shutter in natural light. This is about the best I could manage that way (all shots here are 180L on 7D; this one is 1/4000, f/5.6, ISO 2500).
Then I thought if I set up a couple of flash guns (430EX II's) on low power (I think I used 1/8) for a short flash, maybe I could get better detail and contrast. Knowing that they paid special attention to anything on the surface, I focused on a very small fly on the surface (it also seemed to be carrying a parasitic mite):
Sure enough a fly soon came to carry it off, and I captured the moment (1/250, f/8, ISO 200):
This was about the best I got (the hit rate is not very high, as they fly quite fast), as it came to look at a winged aphid in the water. The front pair of legs are held upwards out of the way.
This shot should give me sufficient detail in the wing veins to narrow down identification. However, from appearance and behaviour, I'm already suspecting that these are Hilara maura, a type of Empid fly, also known as dance flies.
