Acronicta dactylina Grote, 1874

93-1424

Fingered Dagger Moth

Identification

Adults

Acronicta dactylina is a large powdery medium gray moth (FW length 24 - 26 mm) found in forests throughout the Northwest that lacks forewing dashes that are typical of the genus. The subterminal area adjacent to the postmedial line is usually shaded with gray or brownish gray. The median area is similar due to a diffuse median line that runs through the reniform spots. The basal and antemedial lines are gray, double, but usually incomplete or evident as smudged gray marks. The postmedial line, in contrast, is usually prominent, double with pale gray filling. The inner component is relatively faint, but the outer portion is black, forming a series of lunules between the veins. This line is straight across the distal wing closer to the outer margin than the reniform spot, is drawn sharply toward the base of the wing at the costa and above the fold, and the posterior part is straight to the trailing margin slightly lateral to the position of the reniform spot. The subterminal line is absent, while the terminal line is a series of black spots between the veins that contine as thin lines across the gray fringe. The orbicular spot is variable, absent or a small black oval filled with the ground color. The reniform spot is heart-shaped, gray, but usually incomplete. It is filled with the same dark gray or brown-gray of the median line. The hindwing is white in males, light brownish gray in females, with scattered dark scales, dark veins, very faint gray discal spot and postmedial line, dark gray terminal line that is interrupted by the veins, and a lightly checkered fringe. The head and thorax match the forewing color except that the lateral palpus is dark gray. The male antenna is filiform.

This species can be distinguished from Acronicta americana, an uncommon species that occurs in southern Idaho and southeastern Oregon in the Northwest, by the lack of a long basal dash and less brown tint on both wings. Only rare specimens of A. dactylina have an anal dash, and this is short and inconspicuous unlike the long thin dash of A. americana. Acronicta dactylina could potentially be confused with Polia piniae, a common large blue-gray member of the tribe Hadenini with which it flies. This species has fine hairs on the surface of the eye, lacking in the subfamily Acronictinae. Its orbicular and reniform spots are much larger than those of A. dactylina, and it has two prominent dark spots at vein 1A+2A near the anal angle that A. dactylina lacks. 

Larvae

Larva is densely covered with tufts of bright orange hair dorsally and white hair laterally.  In addition, there are two different forms of the larva in the Pacific Northwest.  One form has three long black tufts of hair on the back, and is illustrated under the name of A. dactylina by Powell & Opler (2009).  The second form lacks these black hair tufts, and is illustrated under the name of A. hesperida by Miller & Hammond (2003). 

Habitat

This species is common and widely distributed in cool, moist forest habitats.  In the Pacific Northwest, it occurs in coastal rainforests and mixed hardwood forests at low elevations west of the Cascades, in mixed hardwood-conifer forests at middle elevations in the Cascades and Rocky Mountains, and in riparian zones along creeks and rivers at lower elevations east of the Cascades.

Distribution

Pacific Northwest

Acronicta dactylina is nearly ubiquitous in forests in our region, including on both sides of the Cascade Range.

Global

This species is found in northern California and across boreal North America to the Atlantic. It is most commonly found near the Canada-United States border across most of its range, but it is found from Newfoundland to Georgia near the Atlantic Coast. It has been found to central Alberta and Manitoba in central Canada and as far south as western Wyoming in the Rocky Mountains.

Life History

Larvae

This species feeds on various hardwood trees and shrubs, but appears to particularly favor birches (Betula spp.) and alders (Alnus spp.) in the Betulaceae, and willows (Salix spp.) in the Salicaceae as larval foodplants.

Adults

Acronicta dactylina has a long flight season that begins in late May and lasts through the summer. The peak flight is in June and July. It is nocturnal and comes to light.

Economic Importance

None.

Literature

BugGuide

Covell (1984)

Miller & Hammond (2003)

Moth Photographers Group

Powell & Opler (2009)