Polyphemus moths are found in every state except Nevada and Arizona, and of course Hawaii and Alaska. In northern states, they emerge in mid to late spring, and only have one brood per year. In southerly states, adults have been found in almost every month of the year, and there are often two to three broods per year. Larvae feed on oak and maple, and the large green mature caterpillars may be seen crawling across lawns and parking lots in late summer looking for a place to spin their cocoon and overwinter.
I won't overload this site with an entire series of the photos I took, but here are a few that best show the complete process from emergence to flight. To give an idea of scale, the cocoon is approximately 1.5 inches long, and the adult wingspan is about 5 inches.