Caterpillar Prolegs

caterpillar showing true legscaterpillar showing true legs and prolegs

Although caterpillars of different families have a different number of legs, they all have 3 pairs of true legs attached to the thorax, one pair attached to each thoracic segment. The true legs are segmented and often have a claw at the end. They are retained through pupation and transform into the legs of the adult during metamorphosis. The six true legs can be seen quite clearly in the first photo above.

Caterpillars have additional paired legs called prolegs, which are used for walking and attachment. They are cylindrical, unsegmented and each pair is attached to one abdominal segment (although not all abdominal segments bear them). Each proleg has crochets, or microscopic hooks, that act like suction cups to facilitate movement on, and attachment to, various surfaces such as leaves and branches. In the second photo above, the true legs and prolegs can be easily distinguished: the six true legs are small and positioned close to the head while the prolegs are large and are used to cling to the branch.

During metamorphosis the prolegs disappear and the butterfly or moth emerges bearing only the six true legs.

Photos courtesy of Keith Power, Toowoomba, Qld.