If the caterpillar is big, you can guess the adult moth will be big too. Bedstraw Hawkmoths have a wingspan of up to three inches. Once the caterpillar is fully grown, this beauty will pupate and spend the winter underground in a loose cocoon. They are a far-ranging species, found all across the northern US and southern Canada, into Alaska and the Yukon Territory. They are also found in Eurasia.
Photo by Amy E Parsons on 9/7/20 in White Sulphur Springs, MT