My guess is that it's a black swallowtail, though the image leaves a lot to be desired.

Underwing pattern is like that of the Pipevine Swallowtail. Many orange spots are missing because of HW damage.

The incessant fluttering (when nectaring) is also a habit of this species.

I was looking at the underwings of both on the web and the orange spot that is visible really looks circular like the pipevine's. Hope to see it again to confirm.