Bears’ Last Chance for a Nutritious Feast: Moths


The temperature drop before the formal onset of winter means that bears around the country will be foraging for food to sustain themselves through their upcoming hibernation periods. Bears are known for their varied and undiscriminating diets, which can include berries, fish, deer, elk, and even looting the occasional trash bin. However, one of their most important dietary staples are in fact moths, specifically the army cutworm moth.

Beating out elk and deer in calories pound for pound, cutworm moths are vital for bears building their winter reserves. Every year moths from across the Great Plains and the Intermountain West fly to higher elevations during the summer. Right now Rocky Mountain bears and Yellowstone grizzlies will be feasting on the last of the migrating moths before they fly back to the lowlands to lay eggs. According to University of Nevada researcher Hillary Robinson, bears can consume half their annual energy intake in about 30 days while on a diet of cutworm moths. This is not surprising, since mating moths make an easy meal and bears can eat tens of thousands of cutworms a day.

While a boon to bears, farmers consider the moths to be a worrisome nuisance. Cutworm moths are named for the primary characteristic of its caterpillars, which are voracious plant eaters. Cutworm caterpillars will eat the first plant they see, cutting it down and dragging it into the dirt before feeding. Cutworms will often destroy a plant and eat a little before moving onto the next one, a wasteful behavior that is all the more devastating when they hatch near agricultural crops. The hatching of thousands of cutworms can result in widespread damage.

Despite their detrimental effects on agriculture, cutworm moths are a vital food source for bears across their range. Moth migrations in early summer and fall can cause bears to move around in search for high-energy meals, which can sometimes lead to conflicts with humans.

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