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A medium-large (4.5-5.5 cm wingspan) moth with powdery grey forewings with darker markings and white hindwings. Forewings with the normal markings somewhat broken and blurred, the outer part of the postmedian line and a partial reniform spot most prominent. The orbicular spot a small, hollow ring. There is no basal dash. The anal "dagger mark" is blurred but obvious. The male hindwings are white with grey scales along the veins. The female is larger and is more heavily dusted with grey on the hindwings. Antennae in both sexes are simple. Most likely to be mistaken for the American Dagger Moth, which is darker grey-brown on both wings and has a doubled, white-filled postmedian line, or the Cottonwood Dagger Moth, which is smaller and has narrower wings with a basal dash on the forewings. This large grey heavy-bodied dagger-moth is fairly common and widespread in Alberta. The large, pale and poorly marked western populations of A. dactylina found in Alberta were until recently treated as a separate species, A. hesperida (Large Grey Dagger-moth). Both "species" were listed for Alberta by Bowman (1951). Occassional grey-black melanic specimens have been seen from the coast of BC.

A. dactylina is a solitary defoliator of a variety of deciduous trees and shrubs, and is usually associated with poplars in Alberta. There is a single annual brood, which overwinters as pupae. Adults come readily to light. The larvae (see Ives and Wong, 1988 p.124) are covered with stiff brown hair dorsally and yellow or white hair laterally, with several small tufts of longer black hair.

In Alberta, larvae have been collected from poplar (Populus). Elsewhere reported larval hosts include a variety of deciduous trees and shrubs, including including Red alder (Alnus rubra), birches (Betula), hawthorn (Crataegus), willows (Salix) and other deciduous trees and shrubs (see Prentice et al, 1962 and Rings et al, 1992 for more comprehensive lists).

Newfoundland west to the Pacific coast and Vancouver Island, south to NC and CO. In Alberta it has been collected throughout most of the wooded areas, including the southern half of the Boreal forest, the mountains and foothills, the Aspen Parklands and along the wooded river valleys of the arid southern grasslands.