The moth buzzed its wings as it lay on the ground for a bit, then quieted, letting me get a very good look, and take this not so good picture. The moth wasn't in either of my mickey-mouse guides, and a search of the web didn't turn it up, or at least produced lists of images of possibilities so long that I didn't have the patience to wait for each to load so that I could compare them. So once again I turned to the BugGuide. And I wasn't disappointed. Within the hour I had my answer: Pandorus Sphinx (Eumorpha pandorus).
This is a very beautiful moth, with a quite stunning caterpillar. There are better images at the Moth Photographers Group here. The caterpillar feeds on Wild Grape and Virginia Creeper, which we have in abundance around here--grape for ever, and Virginia Creeper starting to catch up (because of the warmer winters perhaps). Another caterpillar to keep my eyes open for.
The moth was motionless on the ground when I left it, and gone by morning.