The wingspan of an adult is between 80 and 175 mm (3+1⁄8 and 6+7⁄8 inches). There is a high amount of variation within this species. The colors of the adult are always primarily yellow with red, brown, and purple blotches but can vary distinctly on this.
Imperial moths (their many regional morphs, subspecies, and sibling species) range from Argentina to Canada and from the Rocky Mountains to the Atlantic Coast.