by Jessica Johnsrud, Woodland Dunes Education Coordinator and Assistant Director
I recently received an email from someone who had a large moth in their basement. This was an unusual discovery because it was the middle of winter. They included a photo and after a quick look, I determined it was a Polyphemus moth.
Polyphemus moths are members of the giant silk moth family and one of the largest moths in our area. Other members in this family include: Luna, Cecropia and Promethea moths. Polyphemus moths are the most common of the silk moths and range from southern Canada, into all lower 48 states except Arizona and Nevada, and are found in Mexico.
Polyphemus moths truly are giants, with a wingspan of 4-6 inches. They are named after Polyphemus, the giant cyclops from Greek mythology who had one large eye in the center of his forehead. The connection is clear when you notice the moth has a large eyespot in the middle of both hindwings. The eyespot is ringed with yellow, white and black. Also prominent on this species are large, comb-like antenna. The antenna detects pheromones, chemical messages that are important in the mating habits of moths. In the evening, a receptive female will release pheromones and a male can identify those pheromones up to three miles away!
Once a male and female mate, they stay coupled throughout the day and will separate at dusk. The female will lay eggs the evening after mating and egg-laying may continue for several nights. They are laid individually or in small groups of two or three on the under-side of leaves or another substrate. The eggs are slightly flattened and creamy in color with two brown bands.
Caterpillars will hatch about 10-14 days later and their job is to eat and grow. They feed on the leaves of a variety of trees including apple, cherry, oak, maple, grape, willow and others. They have a clever way of hiding the evidence of their dining – they chew the leaf’s stem (petiole) so the leaves fall off and predators do not see leaves with large holes.
The caterpillar will develop through five instars or stages before transitioning to a cocoon. Once it’s time, the caterpillar will find a leaf or twig on the host tree and make a brown, elliptical-shaped case. The cocoon will over-winter and begin transforming into an adult in spring. Generally, the males hatch first and the females a few hours later.
Adult Polyphemus moths have one mission – to mate. In fact, they don’t even eat as adults and therefore only live for a short period. The moth that was found in the emailer’s basement did not have a mate, but she still laid eggs. Unfortunately, the unfertilized eggs won’t hatch.
The large silkworm moths in general have declined in number over the last several years, and its a shame that this one won’t be able to successfully reproduce. If you find a large cocoon attached to a tree branch in your yard, please leave it be. It might belong to a polyphemus or one of the other beautiful silkworm moths and if you’re very lucky, you may be able to experience seeing it for yourself.
photos- polyphemus moth from Wikipedia, polyphemus cocoon from University of Florida