Clinging to rocks and other substrate and munching on algae below Wyoming’s glaciers are tiny insects no longer than 5 millimeters. A handful of stonefly species populate these high-mountain, Wyoming streams, but this particular one, the western glacier stonefly, holds the unfortunate distinction of being the only federally listed threatened insect in Wyoming. 

Researchers once believed it lived exclusively in a few select streams in the Absaroka and Beartooth wilderness and Grand Teton and Glacier national parks. 

But a team of western scientists recently discovered the endangered western glacier stonefly in not one but eight new streams in the Wind River, Absaroka and Beartooth ranges. 

“We thought it was something that only existed in certain places,” said Lusha Tronstad, invertebrate zoologist with the Wyoming Natural Diversity Database, who led the study. “But that’s the thing about invertebrates, they’re really hard to study.”

Researchers search for stoneflies high in Wyoming’s mountains. (Lusha Tronstad)

Whether or not the news changes the species’ threatened status is undetermined, but what researchers do know is that biodiversity, even for teeny insects in frigid streams, matters.

“An ecosystem is a very connected network, and as one species is affected, you can’t know how the impact will ripple through the system,” said Scott Hotaling, an assistant professor at Utah State University who has studied stoneflies and other alpine aquatic insects for years. 

Where field work and technology meet

Few people outside of the niche science community have likely heard of the western glacier stonefly, known formally as Zapada glacier. As larvae, the insects are between 2 and 5 mm long, living in streams as cold as 34 degrees Fahrenheit and as warm as 43 degrees. 

Few creatures much bigger than a stonefly live in these creeks where the water rushes or trickles out from the bottom of sheet or rock glaciers, Tronstad said. By late summer, the stoneflies emerge from streams as adults, fly around furiously mating for a week or two, lay eggs in those same streams and then die. 

While their range is isolated, Tronstad wondered if it might be a bit more expansive than previously thought. So she applied for and won a grant from the U.S. Forest Service to find out. She and a team studied streams in most of Wyoming’s largest mountain ranges, from the Snowy Range and Bighorns to the Beartooths and Wind Rivers. 

Western glacier stoneflies are diminutive invertebrates that live in cold mountain streams. (Lusha Tronstad)

Unlike counting deer or elk from the air, or estimating grizzly bear populations based on sightings and hair samples, finding an endangered larvae can be a finer art. 

The western glacier stonefly resembles, to the naked eye, five or six other species, Hotaling says.

So to find them, researchers use a specialized net to strain every living thing in sections of water, then collect the samples of stonefly larvae and bring them back into a lab for DNA analysis. A portion of their mitochondrial genome is used for barcoding the individual species.

“It’s cool because it requires old-school, in-the-field work in hard-to-reach places where these stoneflies might occur with new-school genetic conservation techniques to actually understand what we’re looking at,” Hotaling said.  

Small bug big importance 

The western glacier stonefly was placed on the endangered species list in 2019 because of their exceptionally small range which is contracting in response to loss of glaciers due to climate change. The news of additional populations found in other streams may or may not change the threatened status, said Jim Boyd, listing and recovery biologist for the U.S. Fish and Wildlife Service. Scientists always learn more about a species once it is listed, and re-evaluate the status every five years. 

An expanded range “increases the redundancy of species across the landscape, so it lessens the risk to the species from a catastrophic event,” Boyd says. “That’s the good part.”

The bad part is that the creatures are still threatened by melting glaciers. 

“If we don’t know what lives in these areas, we can’t know what we will lose.”

Scott Hotaling, assistant professor at Utah State University

In a world where scientists say species extinctions are increasing at an “alarming rate,” it’s easy to wonder if a 5-mm stonefly existing in only a few streams and indistinguishable from other 5-mm stoneflies really matters. 

They do, Hotaling says, for a couple of reasons. 

The first is the intrinsic value of a variety of species. The second is that humans don’t actually know what role those stoneflies play in a broader high-mountain dynamic. Perhaps none, or perhaps quite a significant one. 

“If you lose enough biodiversity, you will eventually run out of species to fill that role, and the crops we eat and air we breathe depend on functioning systems,” Hotaling said. “Messing up those connections can only go so far, and we don’t know what that tipping point is.”

Rosy finches, for example, are the highest elevation nesting bird in North America and a favorite of birders. They feed on aquatic insects that emerge from streams. The western glacier stonefly could be a crucial source of food for rosy finches and their young at a critical time of the year. 

Researchers don’t know the answers to questions like that yet as they race to document what still exists.

“With headwater biodiversity, the more we look, the more we find, which is a bit of a scary thing when we think about climate impacts on biodiversity,” Hotaling said. “If we don’t know what lives in these areas, we can’t know what we will lose.”

Christine Peterson

Christine Peterson has covered science, the environment and outdoor recreation in Wyoming for more than a decade for various publications including the Casper Star-Tribune, National Geographic and Outdoor...

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  1. Edward O. Wilson, known for his farseeing recognition that little things run the world wrote, “…invertebrates as a whole are even more important in the maintenance of ecosystems than are vetebrates.”
    While the entirety of a stonefly’s connection to an alpine environment may never be known, our lack of understanding does not diminish its importance. I applaud these scientists and appreciate Wyofile disseminating the efforts of their ongoing study.