We believe this is likely the Western Spruce Budworm Moth (Choristoneura occidentalis). It is common in forests throughout the Rocky Mountain Region, where the larvae feed on needles of Douglas Fir, as well as hemlocks, true firs, spruces, and larches. Periodic outbreaks of immense populations can cause massive defoliation, garnering them a reputation as a “forest pest.” Moths emerge from their pupal cases usually in late July or early August, with the next generation hatching and seeking a sheltered place under bark scales or among lichens to wait out until the following spring. 

Photo by: Rose Marchak on 7/6/21 or 7/7/21 in the Red Cliff Campground near Big Sky, MT