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A medium-size (3.5-5.4 cm wingspan) long-winged moth with streaky dull grey forewings and shining white hindwings. The forewings are pale grey heavily overlain with dark grey longitudinal streaking, and lack the sharp black markings found in most dagger moths. The cross lines are absent with the exception of the rather indistinct antemedian and postmedian line, which are jagged and partially filled with white scales. The reniform is usually indicated by a slightly darker blotch, and the area between it and the orbicular is noticeably paler than the rest of the wing. There is a terminal row of black dots between the veins. The hind wings are shining white, except for the terminal row of black dots and a few darker scales along the veins. The antennae are simple and the sexes are similar. The much rarer Acronicta longa is very similar, but has several small dark markings along the lower forewing that gives it a slightly more contrasting appearance.

The Smeared Dagger Moth is a defoliator of a wide range of plants, and in eastern North America has reached pest status on occasion. The larva, known as the Smartweed caterpillar, has bristly brown or reddish hairs dorsally, and a row of yellow, inverted V-shaped yellow spots laterally. There is a single brood each year, which overwinters as pupae. The adults come to light. This species is unusual among the dagger moths in the wide range of larval host plants it uses, including trees and shrubs, herbs and even grasses. These include a number of agricultural crops, and on occasion it has been recorded reaching pest status. Most Acronicta utilize deciduous trees and shrubs as hosts. The larva has been reported to have urticating (irritating) hairs.

No Alberta data; elsewhere a wide variety of trees, shrubs and herbs and even grasses, including willow (Salix), alder (Alnus), strawberry (Fragaria), cattail (Typha), smartweed (Polygonum), fireweed (Epilobium angustifolium), and grasses. See Rings et al (1992) or Handfield (1999) for more extensive lists.

Nova Scotia west across Canada to B.C., north to Lake Athabasca and south to Florida and Texas. In Alberta, it has been collected mainly in the Boreal forest and Aspen parklands regions, north to Lake Athabasca and south to about Red Deer, as well as in the foothills at Calgary.