Walking down a trail and looking under leaves for larvae, I came across this large caterpillar on an elm leaf. I wasn't sure which Polygonia species it was, but was sure I had not seen this larva before! They all have some similarities (the spines for one), but thanks to Ross Layberry (local butterfly expert), I know now which species it is, and no, I had not seen this caterpillar in the past, and I rarely see the adults either. Here is a photo of the butterfly it becomes: http://www.pbase.com/laroseforest/image/122852819