Caterpillar foods: willow, poplar; sometimes apple and cherry (Bugguide)
Larvae of both Viceroys and Red-spotted Purples spend the winter in hibernaculums like this one – made from a willow leaf tied to a branch with silk. I don’t know which species made it – it was empty, and the only one I’ve ever found.
6/26/2012 larva on poplar
6/2/2012 larva on poplar
7/8/2012 fully eclosed butterfly