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A medium-sized (2.0-2.8 cm wingspan) broad winged geometrid moth. The fringe on the upper third of the forewing is dark, resulting in the forewings appearing slightly pointed or falcate. They are dull powdery brownish grey or grey over a dirty white ground, crossed by fine dark antemedian, median, and postmedian lines, and with a small dark spot or blotch just distad to and midway down the postmedian line. The hind wing is dirty white, heavily speckled and blotched with dark grey, with two partial faint crosslines, most prominent where they meet the inner margin, and with a fine black discal dot. There is a narrow dark terminal line, and the light brownish fringe is checked with dark scales at the veins. The larvae reach a length of about 25 mm. The head is yellow-green with darker herringbone pattern. Body is light to medium green with grey and white lines along the back and sides. The larva is described and illustrated in color in both Wagner (2001) and Wong and Ives (op. cit). Adults are very similar to those of M. submarmorata, sexpunctata, unipunctaria, and banksiana. M. unipunctaria and banksiana are restricted to the mountains along the western edge of the province. Sexmaculata is smaller in size and is found only in association with Larch (Larix laricina). Previously known as Semiothisa granitata.

There is a single annual brood, which overwinter in the pupal stage Up to about 150 eggs, usually at the base of needles or on strands of Alectoria lichen. Eggs hatch in 5-14 days, and there are 5 or occasionally 6 larval instars (McGuffin, 1972). The adults are nocturnal and come to light.

Transcontinental in both Eurasia (ssp. signaria) and North America (ssp. dispuncta). In North America found across the boreal forest and mountains in Canada from Newfoundland and Labrador to Vancouver Island and the Queen Charlottes; south in the east to Georgia and Alabama. In Alberta found wherever native conifers are present.