When Birdgirl was visiting in the fall, her sharp eyes spotted this cocoon, attached to a board in the corner of the dark, enclosed entrance to the barn. She thought it was a Polyphemus cocoon. The Polyphemus is a large, handsome silk moth. An exciting find! However, when I read up about cocoons, I learned that Polyphemus moths generally hang their cocoons from a tree branch. Their cocoon is enclosed with a leaf, which may stay on the tree all winter, or fall to the ground.
This cocoon is probably that of a related moth, the Cecropia (Hyalophora cecropia). Cecropia cocoons are fastened to a branch or board or some other flat surface. They are not constructed with leaves and don’t hang down from branches. Cecropia cocoons are typically three to four inches long and vary in colour from pale tan or grey to brown. The outer covering is somewhat angular. Inside, a tightly woven second cocoon with rounded ends surrounds the pupa. Even though it is so tightly wrapped, the pupa is not completely safe. The cocoon may be probed by a bird or investigated by a mouse or squirrel. Parasitic wasps may also lay eggs in the larvae, eventually killing it.
I’ve just been fortunate enough to see a Cecropia on one occasion. These largest of North America’s native moths are spectacular. The photograph below was taken by Slomoz (Marvin Smith). He has an excellent post about Cecropias at Nature in the Ozarks. Smith notes that the release of large quantities of the parasitic fly Compsilura concinnata, introduced to North America to control the also introduced gypsy moth, has contributed to a decline in the Cecropia population.