Hungry caterpillars can cause a lot of damage to your precious plants. Your best defense is to scout your landscape on a regular basis. Look over your plants carefully a couple of times a week. If you see chewing damage, try to find the critter responsible. It's probably a caterpillar. Source: Gardening in a Minute, Caterpillars on Ornamentals

Caterpillars are the larval stage of insects in the order Lepidoptera, which includes butterflies and moths.