This is Citheronia regalis, the hickory horned devil. When this caterpillar reaches maturity it will be called a regal moth, or royal walnut moth. Their larval food plants include walnut, hickory and ash. This one had wandered onto a maple tree when its braches crossed with the walnut it had been living on. Maple is not supposed to be one of its food plants, but it had actually been eating it. I'm not sure if that is what gave it its odd yellow coloration, but this specimen is certainly not colored normally for this species. This is in the family Saturniidae, the giant silkworm moths.
