Monarchs live as caterpillars for 10-14 days. During this time they grow and consume mostly milkweed. From here they enter a chrysalis stage, and emerge as an adult butterfly. I assume the gaudy colors of these caterpillars serve as a warning to predators that the caterpillars are poisonous. This type of warning is called aposematic coloration. I found this caterpillar on a milkweed we planted in Erika's garden in hopes of attracting monarchs.