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A medium-size (3.5-4.0 cm wingspan) dark grey-brown moth, with normal lines and spots all present, but not contrasting strongly against the brown background. The transverse lines are doubled and filled with slightly paler brown scales. The orbicular is round, and both it and the reniform are thinly outlined with dark scales and filled with lighter brown. The hindwings are smoky-brown, paler toward the base in males, with the veins lightly marked with brown scales and a light brown fringe. May be confused with E. comosa, which has different genitalia. Euxoa terrenus can be identified by the following genitalic characters: sacculus triangular with prominent angle on dorsal margin (in most species the dorsal margin is irregular and lobed, or sinnuate, anterior to this angle and straight posterior to it); saccular extensions stout and bladelike; harpe c-shaped and densely pubescent; saccus constricted mesially and extended anteriorly; aedoeagus bilobed. Euxoa terrenus is a member of the large subgenus Euxoa, characterized by the shape of the male vesica, which is 1-2 times the length of the aedoeagus, bends above the apex of the aedoeagus to project dorsally or to the right, and lacks a prominent twist, coil or loop subbasally. The valves are all bilaterally symmetrical except for the lengths of the saccular extensions. Keys to the subgenera and species and illustrations of the genitalia are available in Lafontaine 1987.

A moth of the mountains, found from southwestern Alberta and BC south to northern Utah, Nevada and California. In Alberta they have been collected from Banff -Bragg Creek area and Nordegg south in open coniferous forest at low to medium elevations.