
Appearance
Adult: forewing white with thick black or dark gray lines and one or more dark-scaled veins; AM and PM lines scalloped; discal spot dark, usually surrounded by dark lines; terminal line a series of dark spots; hindwing similar but discal spot not surrounded by dark lines, and veins not dark-scaled.Larva: head green with ten prominent black spots; body yellowish-green dorsally with faint green middorsal stripe; subdorsal stripe white, edged on either side with fine dark green line; supraspiracular area green with pair of wavy broken dark lines; spiracular stripe yellow.
[adapted from description by Canadian Forest Service]
Food
Larvae feed mainly on foliage of Western Hemlock and Douglas-fir; other hosts include Grand Fir, Amabilis Fir, Sitka Spruce, Western Redcedar.References:
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http://bugguide.net/node/view/88329