Caterpillar/ˈkætərpɪlər/ Definition 1 of 3Pro Tip 1/3Metamorphosis Stage Remember, 'caterpillar' refers to the stage before it becomes a butterfly or moth. Children watched the caterpillar, anticipating its transformation. Pro Tip 2/3Natural Context Use 'caterpillar' when talking about nature, insects, or life cycles. The biology teacher explained how a caterpillar changes into a butterfly. Pro Tip 3/3Not Always Fuzzy Caterpillars can be fuzzy, but many species have smooth bodies. That smooth green caterpillar will soon be a moth.