On swamp milkweed.
I had difficulty with this one, it did not key out to being a Bristle Fly because in my key, to get to Tachinidae, a clean arista is needed. This identification though is courtesy of John Carr via BugGuide.
https://bugguide.net/node/view/2151467
Insect that was sitting on that flower for at least a day or two, and even stayed while my wife planted it. I'm curious as to what it is.