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A medium-size (3.5-4.0 cm wingspan) light grey moth. Head and body grey, with a contrasting black thoracic collar. The forewings are light grey, with the costa even paler, especially near the base. The normal lines are obsolete or nearly so, indicated by a few dark scales at best. There is a prominent black basal streak, and the area proximal to the orbicular and between the orbicular and the reniform is filled with black scales. The subterminal line is faintly marked with dark scales, especially near the costa. The fringe is grey. The hindwings are dirty white, with the veins lightly marked with darker scales. The fringe is white. Form nesilens lacks the prominent black markings on the forewings and the thoracic collar. The relatively large size, pale grey color and sharp black markings will separate most tristicula from other Euxoa sp. Euxoa tristicula belongs to the subgenus Pleonectopoda, characterized by the prominent twist or subbasal coil in the vesica of the male. There are no characters that can be used to identify females as members of the subgenus. Keys to the subgenus and species are presented in Lafontaine, 1987. See also Agrotis vetusta.

There is a single annual brood, which overwinters as nearly mature larvae. The larvae feed just below the surface, with the main feeding activity in the fall and early spring. Because of the late season-early season feeding period it is not a serious crop pest. The adults are nocturnal and come to light.

Apparently disjunct, with colonies in Nova Scotia and Maine. The main population occurs from Manitoba and Minnesota west to Vancouver Island, and from the Northwest Territories south to Arizona and southern Califormia. In Alberta it has been collected throughout much of the cultivated region, from Edmonton south.