With a wingspan of up to 6 inches, the adult Polyphemus Moth is the largest species of giant silk moth in MT …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 AZ and NV) 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. Photo by Virginia Heinz on 8/24/19 in Stevensville, MT.