This was one of five swallowtail caterpillars I found in the woods at the conservation area, one of them a very early instar. They were on some small prickly ash saplings. I hope they manage to survive the cold nights and that their food supply doesn't run out, because there is no way they could move to the next patch of prickly ash which is a km away.

These caterpillars turn into the very large, spectacular butterfly seen here: https://pbase.com/laroseforest/image/157084467