Just spotted this today and luckily got an ID right away since it’s so distinctive. (Thanks to bugguide.net for the image.)
This is the four-toothed mason wasp, a solitary wasp that uses existing holes for its nest. Mine was eating the pollen on the clethra. It’s looking a little weedy here, but the scent is divine. You will just have to imagine the wasp cradling one of these blossoms. Find out more at this informative site.