Identification
Adult: forewing dull grayish-brown with brown shading along costa; lines black, toothed, accented with white; large white discal spot outlined in black
hindwing pale grayish-white with lighter dusting of fine brown striations or speckles
Larva: body color variable but usually reddish-brown with low, transverse dorsal ridges and light yellowish-brown lateral patches; head brownish with dark brown herringbone pattern on lobes; middorsal stripe multicolored and expanded posteriorly on segments into circular or diamond-shaped area; abdominal segments thickened at distal end, which, in combination with light lateral patches, give them a "bumpy" appearance, much like a conifer twig
Range
coast to coast in Canada and northern United States, south in the east to Florida
Habitat
coniferous and mixed woods
Season
adults fly in June and July
larvae from August to October
Food
larvae feed on foliage of coniferous trees: Balsam Fir, Eastern Hemlock, spruces, and White Pine in the east, and mainly Douglas-Fir and Western Hemlock in the west
Life Cycle
overwinters as a pupa in soil or debris; one generation per year
See Also
Spodolepis substriataria is somewhat similar, but flies in early spring, usually lacks the large conspicuous white discal spot, and the median area is not darkened to form a broad band (
compare images of both species)
Internet References
pinned adult image plus description and other info (Jeff Miller, Macromoths of Northwest Forests, USGS)
common name reference [Twin-spot Girdle] plus description, biology, distribution, food plants (Strickland Entomological Museum, U. of Alberta)
pinned adult image (James Adams, Dalton State College, Georgia)
caterpillar image plus description, biology, food plants, season (forestpests.org)