Curious, I’d thought I’d seen a rise in these small pollinating flies since the bees took a hit. I agree that the bumble-bees have taken up some of the slack.
They are very small- much smaller than a German or paper wasp. One trick to tell them apart from actual wasps is to look at the antenna. Wasps have long, pendular antenna. Flies not only have 2 wings (not 4, sometimes you can see balancers), they also have shorter rigid antenna.