With a wingspan of up to six inches, the adult Polyphemus Moth is the largest species of giant silk moth in Montana …so it should come as no surprise that their caterpillars are pretty massive too (3 to 4 inches in length when fully grown). They are found all across the lower 48 states (except Arizona and Nevada) and southern Canada. The hungry caterpillars can eat 86,000 times their own weight over the two months it takes to grow until pupation, happily munching on a variety of trees and shrubs including oak, willow, maple, and birch.
Polyphemus Moths spend winter in the pupal stage. Typically, their cocoons are attached to a tree branch, or among leaves or grasses on the ground. Squirrels, woodpeckers, and mice are among the potential predators.
Size: 3 to 4 inches when fully grown
Photos by: Ella Balke on 9/2/22 in Missoula, MT