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Adults are large (6.6-10.0 cm wingspan) long-winged moths that occur in two color forms, purple-grey and yellow-brown. Until recently the yellow-brown form was thought to be a separate species, S. quadriguttatus. The forewings have a darker oblique median band, a darker terminal area and darker spots along the costa. There are two small, silver spots near the wing base. Hindwings are even purple brown or salmon pink, unmarked except for one or two small spots on the outer part of the leading edge. The antennae in both sexes are greatly reduced and hair-like, and separate them from all other large Alberta moths. The similar S. argenteomaculatus (Harris) does not occur in Alberta, and the literature reports for argentomaculatus are errors (Schmidt and Lawrie, 1999).

Females deposit eggs in the vicinity of the host while in flight. The larvae bore into the roots of poplars, willows or alder where they complete the life cycle. The larvae apparently take two years to complete the lifecycle, and adults in Alberta are more common in odd-numbered years. Mature larvae are about 50-60 cm long, with cream-white bodies, brown heads and brown bases of the setae. The adults are crepuscular and are poorly attracted to light.

Labrador and New York north and west to British Columbia and the Northwest Territories, south in the mountains to Arizona. In Alberta, it is most common throughout the Boreal forest and Aspen Parkland regions, less common in the Foothills and Mountains, and along wooded parts of the valleys in the Grasslands region.