The question asks about the transformation of a caterpillar, and the correct answer is "a butterfly." Caterpillars undergo a process called metamorphosis, where they transform into a completely different creature. They start as eggs, hatch into caterpillars, and then form a chrysalis or cocoon. Inside the chrysalis, they undergo a remarkable transformation, eventually emerging as a beautiful butterfly. Therefore, the caterpillar becomes a butterfly through metamorphosis.