It is apparently one of the most common butterflies, according to the
(so of course I haven't noticed it up to now!):
I came back, tried to google for "swallowtail butterflies" and got the id. Apparently, the pupa mimics bird droppings:
It also appears that the Eastern Tiger Swallowtail is the state butterfly of Alabama, Delaware, Georgia, and South Carolina, and is the state insect of Virginia!
The wiki says these butterflies are seen flying high over the tree canopy...so I guess I was very lucky today!
If you want some more photos,