There were hundreds of these small insects flitting around a creosote bush. Mostly they weren't landing but this one did for a few moments when this picture was taken. I am not sure whether this is a fly, a bee or a wasp. I can only see two wings so maybe it's a fly but maybe there's another pair that isn't obvious in the image. Is there something obvious that would make it clear whether it is a bee, wasp or fly? What are the yellow capsules near where the leg and body meet?