Answer: Moths

When you think of the diet of bears in the wild, you probably think of majestic photos you’ve seen of wild bears catching fish or adorably mowing through patches of wild berries. While bears certainly do partake of fish, wild berries, various vegetation, and even (in the case of larger grizzly bears) hunt the young of other large mammals like deer or bison, their diet is more diverse than most people realize.

What many people are surprised to learn is that bears eat insects and that in Yellowstone National Park…they eat a lot of them. Specifically, in the summer when hordes of miller moths descend on the mountain peaks in Yellowstone, grizzly and black bears alike will climb high up above the timberline in search of them.

The moths, by the hundreds of thousands, land on the rocky slopes and burrow down into the loose slide rock on the mountain slopes. The bears will come up the mountain, dig through the loose rocks, and gorge on the moths. The bears can eat upwards of 40,000 moths a day which, thanks to the high fat content of the moths’ bodies, works out to around 20,000 calories. A bear who systematically works the slopes for a month in the summer can consume close to half their calorie needs for the entire year.

The entire cycle of mountainside-moth-infestation to delicious-bear-snacks isn’t just a fascinating one, but a highly beneficial one too. Not only do the bears get lots of calories (a boon in the face of shrinking sources of other high calorie foods in their environment), but the period during which the bears climb high up the slopes of the park coincides with a busy time of year for Yellowstone, which means there are fewer bears down in the timberland areas where the bulk of the visitors are.