This is a red admiral, Vanessa atalanta. This individual is getting old, as it has lost some of the crisp color of newer butterflies.
Red admirals are quite entertaining to watch. They put on a show that starts about two hours before sunset each evening. In areas that are shady they will find the one little patch of sunlight high up in a tree and perch there. They fly out and investigate anything that moves and vaguely resembles a butterfly.
A lot of wonderful information can be found on Dr. Royce Bitzer’s red admiral and painted lady web site which can be found here.
Look for red admirals and enjoy the show.