I photographed this Grizzly Bear in Yellowstone National Park. The photo was taken in June, and the blood on her snout is from an elk that she was eating. Now, her diet has changed. What is she eating this time of year?

This time of year, many of the Grizzly Bears of Yellowstone eat Cutworm Moths. The moths fly from surrounding farmland to high, rocky mountain slopes, where they crawl under the rocks to hide. The bears turn over the rocks, and eat the moths by the thousands, getting more nutrition for less work than they could from other August food sources. The National Park Service estimates that each bear can eat as many as 40,000 moths a day. Each moth has about 1/2 a calorie, giving the bears a 20,000 calorie a day diet.

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