This is footage of a Monarch caterpillar feeding on a Common Milkweed plant. Monarch caterpillars are specialists, meaning they can only feed on one type of plant. They are specialists on milkweed plants making milkweeds the only host plants for this caterpillar. Milkweed plants contain a substance that is toxic to typical predators of most caterpillars, causing Monarch caterpillars to be somewhat unpalatable.