Bears, often associated with diets of berries, fish, or larger game, also consume moths. This specialized habit, observed in specific bear populations, highlights their adaptability and diverse strategies for meeting substantial energy requirements.
The Surprising Diet of Bears: Moths
Certain bear species, particularly grizzly bears (Ursus arctos horribilis) in regions like the Greater Yellowstone Ecosystem and Glacier National Park, seasonally incorporate large quantities of moths into their diet. Black bears also engage in this feeding strategy. The specific moth species is the army cutworm moth (Euxoa auxiliaris), also known as the miller moth.
These moths undertake extensive migrations from agricultural lowlands in the Great Plains to high-altitude alpine areas during summer months, typically July and August. They seek refuge from the heat by congregating in vast numbers within rocky crevices and under talus slopes. Bears access these hidden insects by meticulously flipping over rocks and digging into the scree fields. This feeding behavior is a specialized, seasonal activity, providing a concentrated food source.
Why Moths Are a Nutritional Goldmine
Bears consume moths due to their exceptional nutritional value, especially their high fat and protein content. Army cutworm moths are remarkably energy-dense, composed of up to 83% fat. This makes them more calorically rich than many other typical bear foods, such as berries, roots, or fish. A single moth can contribute approximately half a calorie, making them a concentrated energy source.
This rich energy source is particularly beneficial for bears as they prepare for hibernation. Lactating females raising cubs also greatly benefit from this high-calorie intake. Consuming these fatty moths allows bears to rapidly gain weight and build the necessary fat layers for months of inactivity. Biologists have even referred to these moths as “bear butter” due to their high lipid content.
Estimating a Bear’s Moth Intake
Quantifying a bear’s precise moth consumption is challenging due to the remote and rugged terrain of these feeding sites. Direct observation is difficult, and the feeding behavior is dispersed. Despite these challenges, scientific studies provide estimates of a bear’s daily moth intake.
A single grizzly bear can consume tens of thousands of army cutworm moths in a day, potentially up to 20,000 calories. Scientists primarily estimate consumption through scat analysis, examining bear feces for moth remains. Researchers also observe feeding craters and bear behavior on high-altitude slopes. The exact number of moths consumed varies based on moth availability, the bear’s energy requirements, and feeding duration.