Northern Prairie Wildlife Research Center
Wingspan 4.1 cm. Forewing is pale red-brown with a darker median area, wing edge dentate. This geometrid is common and widely distributed in wet conifer forests of the Pacific Northwest, especially abundant west of the Cascades. Moths fly in mid to late summer. Caterpillars are generalist feeders on the foliage of flowering trees and shrubs, such as maple (Acer), madrone (Arbutus menziesii), snowberry (Symphoricarpos albus), ocean spray (Holodiscus discolor), and oak (Quercus) and conifers, such as Douglas-fir (Pseudotsuga menziesii) and western hemlock (Tsuga heterophylla).
Similar species: Populations in the southern Rocky Mountains are considered to be a separate species, Pero giganteus.