A very large (8.5-11.5 cm wingspan) long-winged moth. The body is brown edged with longitudinal black stripes. The doubled postmedian line on both wings is the only well developed cross line. There are also a number of black longitudinal streaks on the outer half of the forewing and small, light discal spots. Our other large dark sphinx moths from south of the boreal forest are grey, not brown. The adults are similar, but females are larger than males. The larvae are large, pale green with granular skin and pale diagonal lateral streaks. They are easily identified by the four prominent horns on the front end, hence the other common name, the Four-horned sphinx.