What insect order's larvae are called caterpillars?

The insect order whose larvae are called caterpillars is Lepidoptera, the group containing butterflies and moths. Caterpillars are the larval, or feeding and growing, stage in the complete metamorphosis of these insects.

A caterpillar hatches from an egg and spends much of its early life eating. It has three pairs of true legs on the thorax and usually up to five pairs of fleshy abdominal prolegs. As it grows, it molts several times; each interval between molts is called an instar. Most caterpillars eat plants, although a small number are predatory, scavenging, or associated with other insects.

The name can cause confusion because sawfly larvae in the order Hymenoptera may look like caterpillars. In strict entomological usage, however, “caterpillar” normally means a lepidopteran larva. After the final larval stage, the insect becomes a pupa, then emerges as an adult butterfly or moth. The order’s name comes from Greek words meaning “scale” and “wing,” referring to the microscopic scales covering adult lepidopteran wings.