Catocala unijuga Walker, 1858
Once-married Underwing Moth
MN : Hennepin Co.
Minneapolis, 822 ft
July 12, 1980, LG Crabo.
Specimen courtesy of LGCC
Photograph copyright: Merrill A. Peterson
Catocala unijuga, the Once-married Underwing Moth is a large Catocala (FW length 34 - 37 mm) with a mottled powdery gray forewing and a banded dark red-orange hindwing that flies in the eastern part of the Northwest during late summer and fall. The forewing has a slightly pointed shape and strongly scalloped margin. The color is mottled medium-dark gray with a strongly powdered appearance due to a sprinkling of black scales, slightly bluish at the base and in the posterior median area. The median area medial to the reniform and subreniform spots, the anterolateral median area, and mid-subterminal area are lighter whitish gray, as is the filling of the large subreniform spot. The basal line is black, short, limited to the costa. The antemedial line is black, wide with strong lateral and weaker medial components filled with blue-gray, moderately irregular and oriented oblique toward the anal angle from the costa. The median line is dark gray, relatively narrow for the genus, limited to the costa. The postmedial line is black medially and pale gray laterally, thinner than the antemedial line, drawn toward the base adjacent to the lateral reniform spot on the costa, fairly evenly toothed across the mid-wing, connected to the subreniform spot and sharply drawn toward the base in the lower fold, oblique toward the anal angle from the costa to the lower cell, then toward the base to the inward tooth. The subterminal line is whitish gray medially and dark gray laterally, diffuse, evenly zigzag across the wing, parallel to the oblique postmedial line near the costa and parallel to the outer margin below the cell. The terminal line is a series of dark gray lunules between veins followed by a continuous dark gray line. The fringe is whitish gray with a striped gray base. The reniform spot is D-shaped with an irregular lateral border, dark gray with peripheral filling of the adjacent ground and a smaller dark gray D centrally. The subreniform spot is large, dark gray filled with powdery white. The hindwing is dark red-orange with black median and marginal bands. The median band is continuous to the inner margin. The head and thorax are powdery dark gray with darker transverse lines across the collar and along the edges of the tegulae. The male antenna is filiform.
This species can be identified by its large size, apically-pointed powdery gray forewing without a strong blue tint, and dark orange hindwing with a median line that reaches the inner margin. It is most difficult to differentiate from Catocala semirelicta, a more widespread and common species in the Northwest. It has a distinct light blue color on the median area and its hindwing is darker red with a blunt median line that ends short of the margin.
This species is widely distributed in moist forests of northeastern North America, extending westward across Canada to the northern Rocky Mountain region in quaking aspen forests.
Catocala unijuga is found in southeastern British Columbia and adjacent northern Idaho and northeastern Washington in the Northwest. It has been recorded from the Cascades and might occur there in low numbers; however, these records could be misidentified C. semirelicta.
Catocala unijuga is found to the Atlantic from our area, predominantly in the boreal zone of southern Canada and the northern United States. The range extends slightly south of the Great Lakes, with a few isolated records further south. It occurs in the Rocky Mountains in Alberta but not significantly further south.
This species is a foodplant specialist on Salicaceae including both willows (Salix spp.) and cottonwoods (Populus spp.), and it may prefer quaking aspen (P. tremuloides) in the Rocky Mountain region.
The flight period of C. unijuga is late summer and fall, typically in August and September.