Caterpillar legs. Ventral view of an American dagger moth caterpillar (Acronicta americana). Caterpillars have two types of leg. The frontal three pairs (top), or thoracic legs are true legs. They are jointed and have hooks at the ends. These legs are retained throughout adulthood. In this species there are four pairs of abdominal prolegs and a single pair of anal prolegs. Prolegs are cylindrical structures which are have smaller, grasping hooks at the end. These are discarded in adulthood forms. Photographed in eastern Canada.