we have some predatory wasps here that will wander through the herb garden and catch green inchworms, ones i cannot find because they blend in so well. i see their poop, but almost never find them, but these wasps get right in there and catch them. it's cool to watch, and now that i know why they prowl through the garden, i leave them alone. i used to shoo them away thinking they would build a nest, but they were just grocery shopping. it's part of the fun of gardening to see nature in effect. do you know what kind of caterpillar they are? catch one and go to a garden center (a good one) if not and they should be able to recommend something. if it's a good place, they won't think you're weird for bringing a bug to show them, and with any luck they have something or can tell you what wasp or natural predator might help you and how to obtain or encourage them in your area.