Pacific Northwest Moths

Identification

Adults

Apamea occidens is a common, relatively large Apamea species (FW length 18–23 mm) that is found east of the crests of the Coast and Cascade Ranges. It has a mottled gray forewing that is often red-brown in the median area, a strongly medially deviated postmedial line below the reniform spot, and a black spot near the anal angle. The forewing is mottled medium dark gray, lightest blue-gray in the subterminal area, with a black basal dash and long spot at the anal angle that is bisected by the pale subterminal line. The entire median area is often red-brown and the subterminal area lighter red-tinted. The terminal are is mottled darker gray, nearly black above the anal angle. A black median dash is present across the fold in some specimens.  The transverse lines are dark gray, double, and filled with lighter gray. The antemedial line is excurved with apex in the fold and is drawn basad at the veins. The postmedial line is weakly scalloped, is drawn sharply toward the base of the wing so that the horizontal portion touches the large reniform spot and narrows the median area below the cell, curving slightly toward the anal angle near the trailing margin. The median line is gray, variable in strength. The subterminal line is pale gray or luteous, complete, sinuous without a strong W-mark. It is preceded by a black or reddish shade, sometimes forming a series of ill-defined black spots between the veins and a black spot above the anal angle as mentioned above. The terminal line is a series of black triangles between the veins. The fringe is checkered gray. The orbicular and reniform spots are black, filled with paler gray. The reniform spot is large and paler than the orbicular spot. The claviform spot is small and partially fused to the median dash. The hindwing is a pale tan-gray, darker gray on the outer third, with a darker gray discal spot and veins. The fringe is white with a gray inner line. The head and thorax are gray with a slightly barred collar and edges of the tegulae. The male antenna is filiform.

This species can usually be identified by its large size, mottled gray wing with a complete pattern of lines and spots, the abrupt medial course of the postmedial line below the cell, and the black patch at the anal angle. Specimens with red median and subterminal areas are unlikely to be confused with any other species. Entirely gray specimens could potentially be confused with Apamea unita, a very rare species that has only been found in eastern Oregon in our region. It is predominantly gray like A. occidens, but its postmedial line is smoothly angled toward the base below the reniform spot and the subterminal area lacks a black spot near the anal angle.

Habitat

This species is common and widely distributed throughout much of  western North America in various dry habitats.  In the Pacific Northwest, it is common in dry, open ponderosa pine forests, juniper woodlands, and on open sagebrush steppe at low to middle elevations east of the Cascades, but may also be found on dry, rocky ridgetops at higher elevations in the Cascades.

Distribution

Pacific Northwest

Apamea occidens is common throughout our region east of the crests of the Coast and Cascade Ranges as far north as the Lillooet region of south-western British Columbia.

Global

This is a western North American species. It is found from southern British Columbia and Alberta south to western Kansas, northern New Mexico and Arizona, and eastern California.

Life History

Larvae

This species is a soil-surface feeding cutworm that specializes on grasses (Poaceae), and may prefer short bunchgrasses based upon the habitat.

Adults

This species has a relatively long flight season but is most commonly collected during the summer. Records from our region span late May to September, with most records from June and July. It is nocturnal and comes to lights, but it has been observed visiting flowers during the day under cloudy conditions.

Economic Importance

This species is of no economic importance.

Literature

BugGuide

Mikkola et al. (2009) 

Moth Photographers Group