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A rather large (4.3-6.2 cm. wingspan) mostly dark black-brown and white moth. The forewing is white with a dark strip along the costa, widening near the apex, and along the entire lower margin. Hindwing white with a dark blotch in the anal angle. Some specimens, especially from the mountains, have most of the white on the forwing replaced with pale brown, and these greatly resemble P. portlandia from coastal BC. The two species are not known to occur together, with portlandia replacing rimosa on Vancouver Island and the lower mainland of BC. Both sexes are similar, but females are bit larger, darker and with a narrower antennae.

Adults are nocturnal and come to light. Fresh adults may be taken late in the season, indicating a very extended emergence, or more likely at least a partial second generation per year. Overwinters as a pupa. The larvae are solitary defoliators of deciduous trees. They have an anal horn and resemble small sphinx larvae.

Transcontinental across southern Canada, except for the lower mainland of BC and Vancouver Island, south to North Carolina, Nebraska and California. In Alberta, occurs throughout the aspen parklands, the foothills and mountains and the boreal forest north to at least the Ft. McMurray and northern Peace River areas. There are a number of closely related species in the Palearctic region.