I was lucky.
An Eastern Tiger Swallowtail on Asclepias tuberosa, otherwise known as...butterfly milkweed.
On my way out of the BBG yesterday, post a nice hot day of deadheading (it was really nice, once a plateau of hotness had been reached), I swung into the Native Garden, to see what had been happening in the last week. I'm so glad I did. Pictures will follow. And then I saw the brilliant orange of the milkweed, with the butterfly fluttering down as I took the picture. It was perfectly quiet, no one there, just the orange milkweed, the butterfly, the tall trees, me.