The western glacier stonefly is an elusive insect.
It lives in only a few remote areas and spends most of its life hidden among the rocks as an aquatic nymph. When the roughly half-inch adult insects finally emerge from the icy high-mountain streams they call home, they die in just a few short weeks, easily escaping detection.
Researchers require a microscope to identify the bug’s genus and a DNA test to confirm its species while in the nymphal stage, said Lusha Tronstad, an invertebrate zoologist with the Wyoming Natural Diversity Database.
Scientists believed for years the insects lived only in seven streams in Glacier National Park and nowhere else in the world.
So when Tronstad heard of a possible sighting of the rare stonefly in the Tetons, she had to investigate.
Her findings not only confirmed the stonefly’s existence hundreds of miles from Glacier, they also could keep the insect off the endangered species list.
Tronstad spent three summers collecting samples from glacial-fed streams in the Tetons, looking for the hard-to-identify western glacier stonefly.
Also known as Zapada glacier stoneflies, the bugs make their homes in melt-water streams often directly below glaciers. They are small and a nondescript gray, black or brown. They have long antennae, chewing mouthparts and two pairs of membranous wings, Tronstad said. They are hard to identify, even for experts, yet they play an important role in the ecosystems where they live.
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Western glacier stoneflies are shredders, Tronstad said. They take organic matter like leaves and cut them into smaller pieces. The job is important to the carbon cycle, Tronstad said.
“If we didn’t have shredders, that organic matter would just accumulate in the world,” she said.
To find the insects, Tronstad and colleagues backpacked above treeline and collected samples from 15 high high-elevation streams. They found the western glacier stonefly in four.
Tronstad doesn’t know how many western glacier stoneflies exist in the Tetons, or in the world, since proper identification is so difficult. Nor does she or other scientists have evidence that the population is declining. What they do know is that the insects are found only in very specific habitats — glacial-fed streams — and the glaciers that create that habitat are disappearing.
That threat to an already limited habitat is what led the U.S. Fish and Wildlife Services to consider listing the insects as a threatened species under the Endangered Species Act. The agency reported the insects warranted listing in December 2016, but it noted that new information about the western glacier stonefly’s range in August 2016 wasn’t incorporated into its assessment. The agency reopened the comment period Oct. 31 to incorporate Tronstad’s findings, as well as the discovery of the western glacier stonefly in Montana’s Absaroka-Beartooth Wilderness.
Without baseline population data, there isn’t a threshold to keep the insects off the Endangered Species List, she said. The issue is really their future as glaciers melt, she said.
Tronstad didn’t offer an opinion on whether the insects should be listed as a threatened species. Her job is to provide data that can be used by agencies to make management decisions, she said.
But discovering the insects in the Tetons and the Absaroka-Beartooth Wilderness is significant, she said. It’s an expansion of their habitat and range. It also means they could be found elsewhere.
She’d like to search for the stonefly in other places, but future research depends on funding, she said.
In the meantime, she and colleagues have submitted their findings to the scientific journal “Freshwater Biology.” Their submission is under review.
The new public comment period on whether the U.S. Fish and Wildlife Service should list the Zapada western stonefly as a threatened species closes Nov. 30.
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