The general form of larvae are useful for identification.

Eruciform larvae are caterpillar-like, with a well-developed head, thoracic legs, and abdominal prolegs. These prolegs are not true legs and will disappear with the adult form. However, the number of prolegs is often useful for identification. Eruciform larvae occur in the Lepidoptera, Mecoptera, and some Hymenoptera (sawflies).