In the past week since hatching, the caterpillars of the Cecropia moth have grown to lengths of about 1 cm in their resting position. Considering that 9 days ago they were each completely enclosed in an egg of about 2 mm diameter, this is an impressive gain in size.

Caterpillars have two kinds of legs, named according to which part of the body they are attached:

thoracic legs: these are attached to the body segments behind the head. These segments will become part of the thorax of the adult moth, and these legs in the adult moth will be much longer and will allow it to walk and grasp, and
abdominal legs: five pairs of legs, called “prolegs”, one pair of which - the anal prolegs - is located near the rear end of the caterpillar, with the remaining four pairs located between the anal prolegs and the thoracic legs. These legs will no longer be present in the adult moth.

The thoracic legs are segmented with hooked end, while the prolegs are fleshly and hydraulically-powered and have a ring of hooks called “crochets” at their ends.

When feeding, the caterpillars crawl along the margin of a leaf, with their legs straddling the leaf edge.

As they move, their prolegs serve as anchors and their thoracic legs as guides. Their bodies move in a rippling motion as they collapse the length of their bodies, pulling their anal prolegs forward and then sequentially reposition their other legs forward, and then extend their fore-bodies in their direction of travel.

Caterpillar locomotion: a Cecropia moth caterpillar walks along the edge of a lilac leaf.

1st instar Cecropia moth caterpillar in resting position.

In the resting position, the caterpillar’s head is facing down and is even curled under the front of the body slightly. The body behind the head is arched slightly upward with the largest spicules - the stiff projections that bear hairs at this stage - protecting the back and sides.

Within the next couple of days, the caterpillars should molt and become 2nd instar larvae.