by Greg Kornelis
When you think of grizzly bear feeding frenzies, visions of the thousand pound brutes gathered at the stream gobbling up migrating fish come to mind, or you might think of their muzzles smooched against the ground vacuuming up kinnikinnick berries by the thousands, or even the more imaginative could conjure a bear banquet adorned with overflowing pots of honey ala Winnie the Pooh. But what I had never dreamed of was the sight seen by many of the visitors of Yellowstone – bears gathered along talus slopes, digging for moths! Yes, moths. The army cutworm moths of Western Montana are actually an important source of pre-hibernation fat for Yellowstone’s grizzlies with as many as many as 40,000 moths per day ingested by an ambitious furry exterminator.
The moths themselves begin as “army-cutworms” in winter and spring, feeding on plants they cut down as caterpillars and damaging crops and gardens in Colorado, Wyoming, Nebraska, Kansas, and Oklahoma. Summer migrations take many of the adult moths to Yellowstone, Montana to feed on the nectar of mountain flowers. Nutritional content is as much as 72% fat, 28% protein, and 1% carbohydrate. The moths feed at night to avoid the daytime sun and find shelter underneath large rocks of talus slopes where it remains cool and moist. This is where the smorgasbord awaits a swarm of hungry bears whose claws make great tools for overturning grubby hideaways.
As the former abundance of pre-hibernation foods such as whitebark pine nuts and cutthroat trout declines, it is predicted more and more bears will focus on moth feeding, affecting how population counts are conducted in the park.
Fessenden, Marissa. “Grizzly bears find fall feast in well-traveled moths.” Yellowstone Gate. 21 Oct, 2013. Web. 22 Oct, 2013. <http://www.yellowstonegate.com/2013/10/grizzly-bears-find-fall-feast-in-well-traveled-moths/>
French, Stephen P., French, Marilynn G., Knight, Richard R. “Grizzly Bear Use of Army Cutworm Moths in the Yellowstone Ecosystem.” Int. Conf. Bear Res. and Manage. 9.1(1994): 389-399. Web. <http://www.bearbiology.com/fileadmin/tpl/Downloads/URSUS/Vol_9/French_French_Vol_9.pdf>
Cranshaw, W. “Miller Moths.” Colorado State University. Web. 22 Oct, 2013. <http://www.ext.colostate.edu/pubs/insect/05597.html>