These wasps belong to the Sphecidae family. All the experts say that they are difficult to identify to species, so I'm content to leave it as Ammophila. The females excavate burrows in the ground which they provision with a paralyzed caterpillar or sawfly larva. They lay their eggs on top of the paralyzed prey, thus ensuring that their youngsters (the larvae) can begin eating immediately. A bit gruesome, given that the prey is not dead, just paralyzed. These Ammophila wasps are interesting in another way too, for when they head off to capture prey with which to stock their burrow, they will roll a small stone along the ground to block the hole, and I've watched them do this several times. Quite clever, I think.