Cicada killer males, though lacking a stinger, will attack their reflection in a window as they are highly territorial, but I think they are solitary and there should be no mistaking them as they are HUGE (almost an inch and a half long)
I got a closeup view of a female taking down and stingng a cicada to death a couple weeks ago and it was both fascinating and gruesome at the same time.
Cicada Killer Pic