Additional photos that didn't seem to make the post:

Shoulda pointed out I'm in Northern NJ, zone 6.

Perhaps Sphex pensylvanicus, sometimes called the great black wasp. IF SO, it poses no threat to your caterpillars.

I agree, it also appears to be on one of its favorite plants for nectar and according to wikipedia it preys mainly on katydids and grasshoppers. Have seen many here in Michigan; they don't seem to be particularly aggressive, at least not while getting their pix taken, but I never attempted to provoke one to test that theory.