MSU Scientist Counts Moths Munched by Grizzlies



MSU Scientist Counts Moths Munched by Grizzlies

By Evelyn Boswell

9/95 updated 11/96 BOZEMAN -- A grizzly bear is a farmer's friend when it comes to getting rid of army cutworm moths. Grizzlies eat the moths in large quantities, says a former MSU biology graduate student. The larval stage of the moth plagues farmers by "cutting" through grain stems. Don White Jr. spent four summers watching grizzly bears in Glacier National Park, and he's come to the conclusion that army cutworm moths are invaluable when the bears can't find enough huckleberries.

Each moth has enough fat in August to make it worth half a calorie, said White, who completed his doctorate in biology at Montana State University-Bozeman in 1996 and then took a position at the University of Southwestern Missouri. Since grizzly bears eat 20,000 to 40,000 of these "lipid Chiclets" in 24 hours, they're getting a significant number of their calories from moths. In 30 days alone, the grizzly bears devour at least 300,000 calories from moths, which amounts to about one-fourth to one-third of the total number of calories they need to live for a year.

Grizzly bears in Glacier Park eat moths from about mid-July to the first week of September, with August being the prime month for fat moths. Based on past studies of the American black bear, moths could play an important part in reproductive success and litter size for the grizzly bears when huckleberry crops are poor, White said. A bear can spend almost 70 percent of its day eating moths. They find them on rocky alpine slopes that heat up quickly in the summer sun. Temperatures can reach 120 degrees.

For as many as 14 hours a day, White has sat on ledges and watched the bears through a spotting scope as they overturned rocks to find and eat moths. When White and his assistants looked closer, they found up to several hundred moths in a square meter. For the first time since his research began, White went up in a helicopter this summer to look for bears and also help make a documentary about his work. Busch Production, Inc. is including White's research in a wildlife film expected to be released in about a year. Besides gathering more data in general, White buried thermometers this summer to see how the temperature varies within one of the rocky slopes he is studying. White is studying 11 sites in Glacier National Park, six in the northern part of the park and five in the south. The phenomenon of moth-eating grizzly bears has raised so many questions that it could take him 10 years to answer them all, White said. One immediate question is why bears were four weeks late this summer in eating army cutworm moths.

He wants to know more about the biology and ecology of the moths, which divide their time between farms and Glacier National Park. Why do the moths hide during the summer in the crevices and cracks of Glacier National Park? What do the moths do in the rocky debris? How does their location in the rocky slopes relate to temperature? "The moths are really pulling off some interesting things," White said. Harold Picton, White's advisor, added, "Since the army cutworm moth is an agricultural pest, you know there's some obvious links between agriculture, perhaps, and grizzly bears. Do grizzly bears have any effect on army cutworm infestations in the grain crops or not? Even though they eat tremendous numbers, is that pretty much incidental because there are just so many?" Damage to crops is caused by the larval stage of the army cutworm moth, Picton said. White is studying the adult moth that migrates to Glacier National Park during the summer. White's research is significant for several reasons, Picton said. For one, it has implications for park management since climbers hike the peaks where moths are found. "It also has some long-term implications concerning the relationship between Glacier Park and the surrounding area and how the grizzly bear ecosystem in Glacier Park actually operates," Picton said. "It also has significance because white bark pine trees have been driven extinct in Glacier Park by blister rust which is an introduced plant disease and, thus, cannot serve as an alternate food source for the bear," Picton said. Funding for White's research was provided by the Peter W. Busch Family Foundation, the National Park Service, National Biological Service and the Mountain Research Center at MSU-Bozeman.

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