I found this caterpillar on a path in the woods near my house yesterday. It was alive, but just lying there to be run over by a bicyclist or a runner. It didn't object too vigorously to being picked up with a leaf and carried to my backyard.
It looked like there was some black encrustation around the caterpillar's body behind its head. During the photo session, a wasp got interested in the caterpillar and kept landing on the encrusted parts. I don't know what the deal was.
After the photo session I placed the caterpillar in a secluded place in my yard. When I checked on it about an hour later, it wasn't there anymore.
Later, a quick search thru the caterpillar pictures on BugGuide revealed that this was a Hickory Horned Devil, the caterpillar of the Royal Walnut Moth (or Regal Moth, Citheronia regalis).