Garlic is a naturally acidic substance that will kill and repel caterpillars. You can use garlic in a variety of ways. In a spray bottle, mix two cups of water with two spoonfuls of garlic powder. Add a teaspoon of dish soap, which will create an adhesive element that will allow the spray to stick to caterpillars and plant leaves. Spray onto the caterpillars as well as surrounding shrubbery and soil.
If you prefer to use garlic cloves, dice and sprinkle around vegetation, which will repel but not kill the caterpillars unless they come into direct contact with the garlic. To use fresh garlic most effectively, grind a handful of cloves into a dusting, and add to three cups of water in a spray bottle. Spray onto plant leaves and surrounding areas to kill caterpillars, and repeat every few weeks to keep them away.
After you have gotten rid of the caterpillars, make sure none return. You can make a simple repellent from natural ingredients. Hot pepper is a natural insect repellent. Grind and sprinkle hot peppers around the lawn and garden, or mix two cups of water with two spoonfuls of hot pepper powder (cayenne pepper, chili pepper or jalapeno pepper). Spray onto plants and surrounding areas to keep caterpillars at bay, and repeat every few weeks or after a hard rain