Winter in the Pacific Northwest is the time to search the naked branches of deciduous trees and shrubs for the cocoons of the Giant Silkworm Moths. As you walk to a steelhead stream or a lake, through the quiet and apparently lifeless woods, look for leaves that appear to be hanging straight down from the branches. If you examine one of these shriveled leaves closely, you might well see that it is wrapped around a silken case containing the pupa of a moth. There is a good chance that the pupa you have found is that of a Giant Silkworm Moth.
Our native silkworm moths are large, beautiful creatures. Silkworm moths are, in fact, our largest moths. The largest and most common of the silkworm moths found in the Bella Coola Valley, where I often fish, is the Polyphemous Moth (Antheraea polyphemus). This particular moth has a wingspan of four to six inches. The wing coloration varies from yellow-brown to cinnamon-brown, and both the forewing and the hindwing contain eyespots. The eyespot on each forewing is small and transparent, whereas the eyespot on each hind wing is much more spectacular. They are large and connected to large blue-black patches. The other silkworm moth that can be found in this Valley is the Ceanothus Silk Moth (Hyalophora euryalus).
The cocoons are interesting to examine, and well worth interrupting your day for. Later in the season, in May, you can look for adult silkworm moths, flying around night-lights. If you see one, count your blessings, for they are not common – they do not feed and are very short lived. Enjoy them if you see them, but avoid the urge to kill them and put them in your collections. As with many of our rare and beautiful North American creatures, Giant Silkworm Moths are on the decline or have disappeared from many parts of Eastern North America.
The best way to see these moths is to find the large, papery cocoons, put them in a well-aerated box, and wait for the adults to emerge in May. Then set them free.
As they fly about the night sky, female silkworm moths release chemical attractants known as p
heromones, which the males, using their large furry antennae, can detect in extremely low concentrations a kilometer or more away. After mating takes place, the female lays her eggs. Caterpillars emerge from the eggs and begin feeding on the foliage of such plants as alder, birch, gooseberry and wild rose.
When full grown, the caterpillar selects a leaf to hide in over the winter months. First, the stem of the leaf is attached to the twig with silk. This ensures that the leaf will not fall off the twig once the autumn storms hit. Next, the caterpillar uses silk to draw both edges of the leaf around itself, like someone wrapping a blanket around them on a cold winter night. Finally, the caterpillar weaves a cocoon around itself, within which pupation will take place. An adult moth emerges from the cocoon the following May or June.
Our native silkworm moths are not related to the famous domesticated silkworm moths found in Asia, which are the source of most of the silken fabrics. But our Giant Silkworm Moths do produce a strong, copious, lustrous silk. Unfortunately, the caterpillars have proven difficult to rear in large numbers, so they are not useful for commercialization.
Giant Silkworm Moths aren’t of interest to fly fishermen as attractor patterns. They are discussed here, just as a reminder that the natural world you walk through on your way to the fishing waters is far more complex and beautiful than many people realize.
Editors Note: Andrew A. Skolnick is a internationally renowned science journalist and photographer who has won numerous national awards and honors for his reporting in biology, medicine, and human rights. You can see more of his work on his website at: http://www.aaskolnick.com
