Pacific Northwest Moths

Identification

Adults

Acronicta americana, The American Dagger, occurs in the southeastern part of our region and is the largest species in the genus (FW length 26 - 29 mm). It has a medium slightly brownish gray forewing with a black anal dash and complete but relatively faint markings dominated by the postmedial line and dark gray-brown hindwings. The forewing is powdery and even, sometimes slightly darker in the subterminal space near the anal angle. All specimens have an anal dash that crosses the postmedial line; some also have a smaller apical dash. The basal and antemedial lines are double, gray, usually indistinct and faint but occasionally complete. The antemedial line is very irregular. An irregular median line is usually present from the costa to the reniform spot. The postmedial line is double, gray, and filled with slightly lighter gray than the ground color. It is strongly scalloped between the veins, broadly convex toward the outer margin around the reniform spot and straight to the trailing margin below the reniform spot. The subterminal line is absent. A series of black spots between the veins forms the terminal line and are continued through the gray fringe. The orbicular spot is a thin dark circle filled with the ground color. The reniform spot is kidney shaped, dark gray, usually incompletely outlined, and filled with the dark gray color of the median line. No claviform spot is present. The hindwing is light tan-gray in males, gray-brown in females, with diffuse gray discal spot, postmedial line, and light shade near the margin. The terminal line is gray, broken at the veins, and the fringe is white in males and tan off-white with faint checkering in females. The head and body match the wing color, with dark gray-brown on the lateral palpus.

This species is only likely to be confused with Acronicta insita, a more common and widespread species in our region. That species lacks the brown or yellow tint that is present on both wings of A. americana, and usually lacks all dashes. If present, its anal dash is much shorter than that of A. americana.

Habitat

This species is common to abundant in hardwood forests and riparian zones throughout much of North America.  In the Pacific Northwest, it appears to be mostly confined to riparian zones along creeks and rivers at low elevations east of the Cascades.

Distribution

Pacific Northwest

Acronicta americana has been most commonly found in and near the Snake River Plain in southern Idaho, extending to the Blue Mountains of Oregon in our area. It has not been found in British Columbia or Washington.

Global

The distribution of this species is centered on eastern North America where it occurs from the island of Newfoundland and southern Ontario to Florida and Texas. It is found in the Canadian Prairie Provinces, Colorado, and Arizona further West but does not occur in California.

Life History

Larvae

This species is a generalist feeding on a wide variety of hardwood trees and shrubs in eastern North America.  In the Pacific Northwest, however, it appears to be mostly feeding on Salicaceae including both cottonwoods (Populus spp.) and willows (Salix spp.) in low elevation riparian zones.

Adults

The flight period of A. americana extends from late May to early August, with most records from June and July in the Pacific Northwest. It is nocturnal and comes to lights.

Economic Importance

None.

Literature

BugGuide

Covell (1984)

Moth Photographers Group