The Surprising Connection Between Grizzly Bears and Army Cutworm Moths in Wyoming

The barren mountain slopes of north-west Wyoming serve as an unlikely buffet for grizzly bears during the summer months, thanks to the presence of the army cutworm moth. The moths migrate to the area in the hundreds of millions each year, providing a high-calorie food source for approximately 200 grizzly bears. Biologists estimate that each gram of moth offers bears around eight calories, meaning some bears can consume up to 40,000 moths per day. The moths, which migrate from as far as Canada’s Northwest Territories, have remained a stable food source for the bears even as other sources such as whitebark pine nuts and cutthroat trout have been affected by climate change and invasive species. However, human interference and the effects of the climate crisis pose threats to this unique relationship.