This caterpillar has me stumped.

unknown caterpillarIt is resting on a vining milkweed plant, although it might have crawled to there from some other type of plant nearby.

unknown-caterpillar-2

It looks like it has a single, spiky horn, which would be a sphinx moth of some sort. The head doesn’t look any sphinx moth I’ve seen.

Anyone have any ideas what it might be?