I was standing on a sandy Lake Huron beach when this wasp ran up to my shoe and grabbed a previously unseen caterpillar off the sand. Then it dragged the victim to a piece of driftwood, wedged it into place, and worked on its head for a few minutes.
I think this may be a sphecid in the genus Podalonia; another page lists noctuid moth caterpillars as prey of a Podalonia species. I don't know what kind of caterpillar this is but I've read that wasps paralyze them, drag them to a burrow and lay eggs on them, so newly-hatched wasps have fresh food to eat. This can't be much fun for the caterpillar (imagine lying paralyzed on the floor and being eaten alive by a pack of rats) but maybe the wasp also injects a painkiller, so the caterpillar doesn't feel a thing. Yeah, let's say that's what happens! ;)