I recently noticed a number of these common buckeyes (Junonia coenia, Nymphalidae) fluttering around in a nearby prairie. They’re common in southern North America, but they migrate to the northern United States and southern Canada in the summer.
Members of the family Nymphalidae are known as “brush-footed” or “four-footed” butterflies. This is because in most species the front pair of legs are greatly reduced, and are sometimes atrophied. In the photo above you can see that only the middle and hind pairs of legs are noticable on this specimen. If you click to see the full-size image, you can see how small the front legs are.