Giant Silkworm Moths

By William T. Hathaway

Giant Silkworm Moths

The Cecropia or Robin Moth is the largest of our silkworm moths, having a wingspan that may reach 6 in. (12-15 cm). Its overall color may vary to reddish and gray-brown depending on the type of plant consumed by the caterpillar. The male Cecropia, pictured above, has larger antennas and a smaller abdomen than the female of the species.

Cecropia caterpillars are known to feed on the foliage of at least ten species of local shrubs and trees. In winter with snow on the ground Cecropia cocoons are often visible, since the cocoons are spun around and including a twig or branchlet. This cocoon is above the ground and can be seen as it is silhouetted against a snowy background.

Cecropias produce one generation a year, whereas the Polyphemus Moth (lower picture) produces two generations a year. Both moths are similar in size and feeding habit. A large eyespot on the hind wing of the Polyphemus readily distinguishes it from the Cecropia. Tough egg-shaped cocoons of the Polyphemus, although attached to a branchlet by a fibrous stand, tend to fall with the autumn leaves.