A caterpillar is the larval stage of an insect, specifically a butterfly or moth. We know you think the creature in our fanart Caterpillar on Leaf Sticker is an ugly duckling among animals. But look at this cutie! Even before its changes into a beautiful butterfly, it looks so adorable here! By the way, caterpillars play a vital role in the ecosystem as herbivores, and they are also an important food source for many other animals.