Parasitic wasps are the main predators of caterpillars, and we have a healthy wasp population in our back yard :) They lay eggs on/in the caterpillars and then the wasp larvae eat the caterpillar. I took the natural let it balance itself out approach last year but I didn't really comprehend the amount of damage that even a couple of caterpillars could cause once they were larger. They don't just hole up in one place, they eat their way into the bud until they get next to the main stem and then they will eat their way along the main stem, which damages the base of every single individual bud that wraps around the main stem. But you can't see this damage from outside! You have to totally crack open the bud to even see it at all!