Pacific Northwest Moths

Identification

Adults

Acronicta lepusculina, the Cottonwood Dagger Moth, is one of three pale whitish Acronicta species in the Northwest. It is a medium-sized moth (FW length 18 - 19 mm) that flies in riparian areas during the summer. It has black dashes and angular orbicular and reniform spots on a pure white background that is scattered with black scales. The forewing is usually lightly peppered with black scales, most heavily distal to the postmedial line near anal angle. The basal dash is long and thin, with shorter anal and apical dashes in most individuals. The transverse lines are evident as black spots on the costa except for the postmedial line that is evident as a serpentine white area devoid of black scales. The fringe is white with black lines between the ends of the veins. The orbicular spot is a narrow black diamond filled with white, while the reniform spot is chevron-shaped with a dark lower half and faint upper half. The claviform spot is absent. The hindwing is pure white with a thin dark gray terminal line and faint gray checkering in the fringe. The head and thorax are very light gray. The male antenna is filiform.

Acronicta lepusculina is most similar to Acronicta vulpina in our area, another pure white moth with powdery black markings. The black marks on A. vulpina are usually more extensive than those of A. lepusculina, but its basal dash is shorter.

This species is geographically variable and numerous names have been proposed for the many forms. Specimens from the Pacific Northwest are paler white than those from many other areas, including those from California which are gray and resemble Acronicta cyanescens.

Habitat

This species is widely distributed throughout much of North America in riparian habitats along creeks and rivers at low elevations, and in quaking aspen forests at higher elevations in the mountains.

Distribution

Pacific Northwest

This species is found in forests in southern British Columbia and along rivers and streams in the dry interior of the Northwest. It is rare west of the Cascades but has been found occasionally in western Washington and Oregon.

Global

The range of A. lepusculina extends across North America from Coast to Coast. The distribution in the East extend in a narrow north-south band near the Canada-United States border. It is more widely distributed in the mid-Continent and in the West where it occurs from north-central Alberta to Texas, Colorado, Utah, and California.

Life History

Larvae

This species is a foodplant specialist feeding on Salicaceae including willows (Salix spp.), cottonwoods (Populus spp.), and quaking aspen (P. tremuloides).  It is also recorded from Betulaceae including birches (Betula spp.) and alders (Alnus spp.).

Adults

This species has been found from late spring to early fall in our region, most commonly in June and July. It is nocturnal and comes to lights.

Economic Importance

None.

Literature

Covell (1984)

Crumb (1956)

Moth Photographers Group

 Powell & Opler (2009)