Caterpillars (butterfly and moth larvae) can be distinguished from larvae of beetles, sawflies, and true flies by the number and arrangement of their appendages. Caterpillars and larvae of beetles and sawflies have three pairs of true legs, one pair on each thoracic segment. Larvae of most sawfly species also have leglike protuberances (called prolegs) on six or more of their abdominal segments. Caterpillars have prolegs on some (five or fewer) abdominal segments, and never on their first two abdominal segments. Beetle larvae have true legs but no prolegs. Fly larvae (such as predatory syrphids) have no true legs, but some species have prolegs or fleshy protuberances on their abdomen or on both their abdomen and thorax. Credit: Adapted from an illustration by David Kidd
