I believe that this may be a northern crescent. The northern crescent is a butterfly that can be found in a variety of habitats in Canada and the northern half of the United States. They look very similar to the pearl crescent, which over laps most of their range. When I help survey butterflies in the early Summer with the St Paul Audubon Society our guide and butterfly expert usually will not try and distinguish between the two species because they are so similar.
The northern crescent larvae, caterpillar, feeds on plants of the aster family. Eggs are laid in the summer with the butterfly over wintering in the third stage of its larval form. When spring comes the caterpillar wakes from its dormant state and begins to eat. They will go through their final metamorphosis around middle of June to the middle of July.