This is a medium sized (FW length 14-17mm) Geometer of coniferous forests. It is grayish tan with fine speckling, antemedial and post medial lines comprised of dark spots where the pale veins cross them, a diffuse medial line that reaches the costa, and pointed but not hooked (falcate) wingtips.
It is most likely to be confused with Thallophaga taylorata, but that species has falcate wingtips, the medial line does not reach the costa, and the ante- and postmedial dots are smaller and are bordered by continuous brown shading.
Thallophaga hyperborea is a moth of coniferous forests. It’s preferred larval host is Western Hemlock, but the larvae will also defoliate other members of the family Pinaceae (conifers), as well as occasionally being found on alder. They are bivoltine (two broods) in our region with adult flights peaking in March/April and again in June. And possibly, as hypothesized by Powell and Opler in ‘Moths of Western North America’ (2009), trivoltine in California when conditions are right. The larvae which do overwinter will pupate, and spend that time buried in soil in diapause.
Size- FW length 14-17mm
Habitat- Wet Coniferous forests
Range- Primarily west of the Cascade crest in our region
Eats- Larvae feed on foliage of Western Hemlock and other Pinaceae, and occasionally on alder
Flight Season- January to September in our region