These guys are in the thick-headed fly family, Conopidae. And this species is in the special group in the genus Stylogaster. There are only two North American species in this genus: S. biannulata and S. neglecta. But clearly they are a well named genus. This is the male from Norm's yard. They tend to flowers and resemble Syrphids somewhat, though they lack the Syrphid wing vein. Larvae of this family are endoparasites of bumblebees and wasps.

The top view of the male, same individual. Fine splayed antennae.

The female has a dangerous looking ovipositor. Apparently they attach the eggs on bumblebees and wasps while in flight (!!?). I would want a long stick too. The sex act is tough to imagine though there is a shot on Bugguide of the event. Not for the squeamish.

Imagine no more. Here is the sex act from Norm's local group. Not quite as dangerous as I thought. But still. 

This is, I believe, another Thick-head. Only it is in a different genera from the Stylogaster above. Likely a Physoconops (twelve US species). Active nectar feeder in a low wet area at Bell. There were several of them working this field.

Another Thick-head from Cheryl in NE AR. Likely same genus. The hind femur is a separation along with the wing veins from the Physocephala genus.