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Euxoa westermanni is a medium-size Euxoa (FW length 15-17 mm) with dark red-brown, almost black, forewings with the basal two-thirds o the costa and the large orbicular and reniform spots contrasting pale rusty yellow-orange. The hindwings are sooty brown. The light rusty-orange center in the dark red-brown thorax is diagnostic. Euxoa westermanni is superficially most like E. castanea and E. idahoensis. In addition to genitalic differences it can be separated from castanea by the darker ground and the chestnut thorax, and from idahoensis by the smaller, less contrasting spots and the chestnut thorax.

Euxoa westermanni has a northern distribution, ranging from southern Greenland and eastern Labrador west to Great Slave Lake and central Yukon, south in the Rocky Mountains to Lake Louise, and to near Calling Lake in the boreal forest of central Alberta.

Euxoa westermanni is an arctic species of Euxoa, reaching our area along the eastern front of the Rocky Mountains and in the boreal forest south of Calling Lake. I have found westermanni at Brown Creek Recreation Area just northwest of Nordegg, in well-drained mature pine-spruce forest along the creek floodplain. Chris Schmidt and I also collected a single specimen in a large fen over permafrost in the boreal forest just south of Calling Lake.