The Giant Silk Moths of North America

Forrest M. Mims III

Around 42 species of giant silk moths inhabit the continental United States.

Many of these moths are quite attractive, especially the Polyphemus moth (Antheraea polyphemus). This giant moth is among the largest, and its wing span can exceed 14.5 cm (5.75 inches).

The Polyphemus moth has been found in all the adjoining United States except Arizona and Nevada. The adult female Polyphemus moth may lay two or three eggs on leaves of certain trees, including oak (Quercus), willow (Salix), maple (Acer), and birch (Betula).

When the baby caterpillar emerges from its egg case, it first eats the shell. It then begins munching on its leaf.

As the bright green Polyphemus caterpillar grows, it devours entire leaves and slices off what remains.

If the Polyphemus caterpillar survives hungry birds and other predators, it will eventually grow up to about 9 cm (3.5 inches) long. It then spins a silk cocoon around its body and begins to transform itself into the beautiful Polyphemus moth.

When a male Polyphemus moth emerges from its cocoon, it has only one goal in life. That it to find a female with which to mate. The female attracts the male with a special perfume called a pheromone. The male detects the pheromone by means of its antennae, which are much larger than those of the female.

The adult life span of the Polyphemus is comparatively brief. That’s why neither male or female has a mouth. They fly only at night to avoid birds and other predators.

The most characteristic features of the adult Polyphemus are its large eye spots. These are pairs of matching patterns on each of its wings. The larger eye spots on the rear wings closely resemble the eyes of an owl, and some scientists believe that this scares away potential predators.

It doesn’t scare away all of them, for the specimen in the nearby photograph (Fig. 1) was captured by a bright red male northern cardinal (Cardinalis cardinalis) near where we live. Much to the bird’s displeasure, I rescued the moth and brought it home to make photographs.

Polyphemus moths rarely cause significant damage to trees. So there is no need to kill the moths by spraying your trees with insecticide.

You can learn more about the giant silk moths of the US from various insect books and the “Moths of North America” web site of the Northern Prairie Wildlife Research Center, where I found some of the facts in this column.

Forrest M. Mims III and his science are featured online at www.forrestmims.org and www.sunandsky.org.