(Thank you, bugguide.net, for the identification!)
The larvae feed on cypress, locust, and hawthorn. By far the most likely host plant for this individual was one of the numerous Black Locust or Honey Locusts along McDowell Creek.
The adults feed on shrubs, trees, or--as here--flowers!
In fact, this one had his head buried in the blossoms to the point that I never got a chance to see if it really is "flat."
I was struck by the differences between his thorax and wings--and the strange perforations in his wings. His wings look porous--like Triscuit crackers.
He has a look-alike cousin (Acmaeodera mixta) that apparently can be distinguised only by the colors on the wing tips. A. pulchella's are all black; A. mixta's are mixed with yellow.