Limenitis arthemis. And it's bizarrely small, maybe 3 inches wide at most. I've heard of small generations of other Lepidoptera being born but it was always attributed to poor leaf quality, occasionally species having to eat leaves that had already fallen off of trees. I don't think that's what happened here. In the last two instars I was picking leaves fresh off the tree in groups of four to seven and the caterpillar consumed them all in one sitting. My only thought on this is either it's somehow beneficial to be smaller than typical during the winter months (when these dwarf versions tend to occur) and must be somehow triggered by either chemicals in the tree leaves it consumed and/or hours in the day.
I did notice the White Snowdrift Crabapple retained its leaves, and still has them on the tree even now, where as the native American Plum, Beach Plum and Black Cherry have all already dropped their leaves. It also had ripening fruit on it, so maybe it's just a result of hosting on Apples instead of Plums at this time of year. (They can use both).