I think this is a Buckeye, but it is so hard to tell from the photos in the books.
If anyone knows, I would appreciate the information. He is beautiful on the Purple Coneflower.
Thanks to jypsee I'm told it is a Common Wood Nymph. It is on the edge of its range here, so I am very excited to see them. They were not here last year, but there are several this week. Thanks, jypsee!