Great Plains Miller Invasion Is Bear Feast

Great Plains Miller Invasion Is Bear Feast

Most of us living in western Kansas open our mailboxes or newspapers to find multitudes of miller-moths hiding in dark crevices. After slapping at the annoying creatures, we scrub away miller dust that  their wings deposit. If they escape, they squirt orange fluid that scientists call meconium to provide an idea of its ingredients. Most people can’t find anything good to say about this insect invasion except, “Thank goodness they don’t eat fabric, wood, or carpets.”

In pre-miller life, these invaders were army cutworms that sometimes wreaked havoc in winter wheat fields and alfalfa patches. In high population years, cutworms assume the “army worm” custom of massing in Biblical plague formations to travel over fields or highways. 

After they mature in spring, they tunnel into soft earth to pupate. Following a three to six week period underground, they emerge as flitting moths, squeezing their way through door and window cracks to slink into inviting darkness.

Fortunately, they do not hang around all summer. These are high elevation, cool weather, wildflower- nectar loving creatures. They migrate from the plains into the high reaches of the Rockies. By August, life balances itself, and army cutworm moths that survived this journey may build winter fat stores of four-legged eating machines.

Grizzlies and black bears love miller-moths. Recall that these insects love dark crevices. Vast mountain rockslides provide innumerable hidey-holes for migrating throngs. Bears follow them to boulder-strewn slopes to feast. According to researcher Hillary Robison who observes bears in and around Yellowstone Park, “It’s kind of like a salmon stream. We’ve seen bears feeding within several hundred yards of each other. . . .”

Some people with sensitive noses may notice unpleasant odors coming from dead moths. This scent results from a high fat content that turns rancid when miller-moths die. This ½ calorie of fat content per moth draws grizzlies to high mountain slopes and triggers their focused digging into rocky crannies. Bears can eat up to 40,000 moths a day.

Robison’s research examines how far Yellowstone moths travel from Great Plains farmlands and reveals an unexpected connection between the Great Plains and bear survival in Yellowstone. Of interest to Yellowstone tourists, silvertips looking for moths in high elevations each summer will not be inclined get in trouble bothering summer park visitors at lower elevations. According to Robison, “If they are spending a month up in these Yellowstone moth sites in the summer, they could eat close to half their needs for the year.”

While I don’t like moth dust, orange splats on the woodwork, or having winged hordes fly out of my newspapers, I have a new appreciation for these metamorphic wonders. I enjoy knowing miller-moths that hovered about my yard light help fatten grizzlies for winter hibernation.