In the middle of a riffle on the Madison River, Jackson Birrell is sprawled across river rocks, pushing all his weight on a metal bucket. He’s looking for bugs.
Birrell, an aquatic entomologist and executive director of a nonprofit called The Salmonfly Project, has the look of a surfer: an angular face and athletic build with shoulder-length dark hair. But Birrell spends most of his time in freshwater, not the ocean. Today, he’s clad in waders and a trucker hat.
The bucket, known as a Hess Sampler, was named after scientist A.D. Hess who invented it in 1941. The Sampler captures exactly one square foot of the river bottom. Birrell grabs rocks, scrubbing and scraping until they’re bare of all mud, moss and, of course, larvae. A net dangles from the sampler like a tail, wagging in the current, to capture everything that comes off those rocks: a smorgasbord of macroinvertebrates.
We’ve hit this stretch of the Madison at what Birrell expects to be the very beginnings of the area’s legendary salmonfly hatch. Salmonflies — Pteronarcys californica — are an iconic and instantly recognizable species for anglers. Black with splashes of bright, pumpkin orange, they’re huge; as large as a pinky finger. They crawl out to the banks and hatch from larva stage to magnificent winged arthropods.
“They’re kind of the grizzly bear of the angling bug world,” Birrell says. “And they’re one of the few aquatic insects that we know are in decline.”
For mediocre flyfishermen like me, the salmonfly hatch is the most exciting time of the year on the river. Your casts can be sloppy. Rather than spooking trout, slapping the water with the weight of a fly can alert fish to the presence of a tasty meal. Trout rise for the easy pickin’s. In lots of ways, salmonflies are the region’s most charismatic microfauna.
Birrell is one of the small smattering of scientists paying attention to the underwater entities we all tend to overlook, and how we can better grasp their little-understood plight. These bugs are a lens into the world of the unsung and the taken-for-granted, but also a much larger picture. Aquatic insect communities show us the history of abuse on our waterways, as climate change and development take their toll. According to the data Birrell is collecting, changes in these invertebrate populations in the Greater Yellowstone Ecosystem could portend monumental shifts in fisheries, economies and ecosystems.
“On our fisheries, especially in Montana — the Madison, the Yellowstone, the Gallatin — the fishing is still awesome,” Birrell says. “The bugs are still diverse, the hatches are still really good. But what we’re starting to see is early warning signals of more changes to come.”
A Serengeti underwater
Most aquatic insect aficionados are anglers. But growing up, Birrell never so much as held a fly rod. He had no interest in bugs as he started pursuing science in college. As an undergrad at Brigham Young University, though, he was looking for field experience. “The labs that I wanted to work with, like fish labs and reptile labs, didn’t have any room,” he says. “The only option was a bug lab. I thought that was lame.”
Soon, he found himself in class on the Provo River in Utah, flipping and scrubbing rocks. When he lifted his net above the surface, he was blown away.
The richness of insect life in trout streams like the Madison, Gallatin, Yellowstone or Henry’s Fork — or, in Birrell’s case, the Provo — is staggering. More than 100,000 species of insects spend some part of their life underwater. Compare that to life above rivers and seas: scientists have documented roughly 11,000 bird species, about 6,500 mammals, and approximately 21,500 species of reptiles and amphibians. According to Birrell, bugs represent about 70 percent of aquatic biodiversity overall.
How many bugs are there? Surveys show more than 1,000 insects per square foot on most trout streams, Birrell says. Not mile. Foot. It’s a dizzying array of life. Even casual anglers often know the big three: stoneflies, caddisflies and mayflies. There are also true flies — things like midges and mosquitoes and black flies — along with dragonflies and damselflies and aquatic beetles.
Most aquatic insects lay their eggs underwater or near it. The bugs hatch and crawl as squirmy larva, clinging to riverine cobbles. When they reach maturity, they undergo metamorphosis — much like a butterfly — and emerge with wings, flying into the air. They’re extremely promiscuous and also short-lived. They die naturally within hours, days or weeks, or else become food for birds, fish, amphibians and reptiles, or even splatters on our windshields.
Some bugs eat algae. Others, known as “shredders,” feed on leaves and other detritus, cycling nutrients through the ecosystem. “Aquatic insects in general are bioindicators of water quality,” Birrell says. “The aquatic insect community will change faster and more strongly than trout or other critters in response to stress.”
The richness of a bug’s life, along with its unique life history, flipped a switch for Birrell. In fact, Montana State University ecology professor Lindsey Albertson underwent a similar metamorphosis. She fell in love with bugs pursuing her Ph.D. at the University of California-Santa Barbara.
Albertson calls insects like net-spinning caddisflies “ecosystem engineers,” a term often reserved for much larger fauna like beavers. They’re tiny. But bugs matter. These caddis, for example, construct tiny structures, almost like spider webs, that capture floating detritus. And they’re territorial; they chirp at one another, claiming, in insect terms, “This is mine!” Birrell calls these interactions “rap battles.”
“In the terrestrial environment, it’s kind of easy to see what’s going on,” he says. “You’re hiking through the woods, you see the birds, you see elk. In a river environment, everything’s flowing. You can’t really see it. You can’t really interact with it. But then when you start learning about it there’s this invertebrate Serengeti down there in the cobbles.”
Anecdotes and a dearth of data
For years, anglers have picked up on declines of major hatches they depend on for livelihood and leisure in Greater Yellowstone. But absent rigorous scientific data, angler evidence exists only as anecdotes.
Richard Parks moved to Gardiner, Montana, in 1953. At 10 years old, he occasionally relieved the clerk up front and cut his chops tying flies for his dad, the founder of Parks’ Fly Shop. “Nothing like captive child labor,” he tells me over the phone in late June from the back of his shop.
Not long after, Parks witnessed a major shift in the region’s aquatic ecosystems. During his early teens in the 1950s, the federal government picked a fight with a menace in the timber in and around Yellowstone National Park: the spruce budworm. To win the battle against the bug, the federal government recruited pilots to spray the infamous chemical insecticide DDT over roughly 275,000 acres encompassing both the park and the Gardiner basin to the north.
The spray rained down on the river and forests alike. It wrought destruction, but not only of the kind the government hoped for. Osprey, eagles and mink suffered. So did insects and fish. According to Parks, the brunt of the visible damage to the watershed came months later, when brown trout began to spawn. “We had miles and miles of the Yellowstone River literally lined with dead fish,” he says.
The “spray job,” as Parks calls it, was featured in Rachel Carson’s 1962 landmark book, Silent Spring, which ultimately led the federal government to ban DDT. “Aquatic insects and other stream-bottom fauna were reduced to a tenth of their normal population,” Carson wrote. “Even by the end of the second summer after spraying, only meager quantities of aquatic insects had reestablished themselves, and on one stream — formerly rich in bottom fauna — scarcely any could be found. In this particular stream, game fish had been reduced by 80 percent.”
The insects recovered, Parks says, with one exception. Today, the Mother’s Day caddis hatch is among the most famous in the region. In early May, the tiny flies explode with life on area riverbanks. During years when runoff doesn’t cloud the water, it can be an angling bonanza. But back in the DDT days, Parks says, the hatch wasn’t around Mother’s Day at all. It came in March or April. “It was earlier and lasted longer,” he says. “But just as prolific.”
After DDT doused the landscape, anglers reported just two individual caddisflies, separated by dozens of miles. It took decades for the beloved hatch to recover. Today, the bugs are back, Parks says. “But it took literally 35 years to reestablish the population.”
“If we lose our wild rivers and our clean air and clean water in this Yellowstone area, we’re going to lose everything. It’s going to have a cascading effect.”
craig mathews, founder, blue ribbon flies, west yellowstone, Montana
While some changes come from single, cataclysmic events, others are harder to pin down. Craig Mathews started Blue Ribbon Flies in West Yellowstone in 1979 and he literally wrote the book on fishing Yellowstone (and many others). He’s been paying close attention to the region’s aquatic insects, and the trout that feed on them, for decades. “I could never build model planes when I was a kid,” says Mathews, now 76. “But I could tie flies that caught fish.”
He’s noted declines of salmonflies, pale morning duns, caddis and more. The absence of one hatch in particular, he says, has him and other anglers flummoxed. “We used to fish tremendous hatches of mayflies,” Mathews says, referencing the summer-month hatches of small insects with long, arcing tails and wings that sweep up into the air, rather than down onto their backs. “They have just really been on the decline.”
In particular, the Drunella flavilinea, or flav — a small relative of the western green drake — more or less disappeared. Mathews’ shop tied thousands of flies in preparation for the spectacle. Then, he says, “all of a sudden one year, they didn’t show after they had showed for 30-plus years in huge numbers. You saw maybe 100 where you saw 100,000 before.”
Guides, he adds, are already sensing these changing hatches. Clients seek the hatch in new areas or abandon plans entirely. It’s a disaster that could hit ecosystems and the angling market at the same time. Fishing generates about $1.27 billion a year for the Montana economy alone. Greater Yellowstone rivers are among the most popular in the state. Anglers spend hundreds of millions more in Wyoming and Idaho, too, fishing the Shoshone, Henry’s Fork, Snake, and other prized trout waters.
After the flavs began disappearing, Mathews says, old-time anglers and guides began scratching their heads. They weren’t just concerned about their stockpiles of unsold flies. They were worried about the ecosystem. “I’m not a scientist,” Mathews says. “But it goes hand in hand: fewer insects, fewer birds, fewer rising trout. It could be a real disaster.”
And it’s not just flavs, either: Mathews has also seen salmonflies decline on the Lower Madison, and Parks has watched as the salmonfly hatch moved more than 30 miles upstream over the decades on the Yellowstone. Parks is also an angler, not a scientist. “But that could be pretty directly correlated with, if not caused by, water temperature,” he speculates.
“If we lose our wild rivers and our clean air and clean water in this Yellowstone area, we’re going to lose everything,” Mathews says. “It’s going to have a cascading effect.”
The new science of salmonflies
While anglers like Parks and Mathews can paint a colorful picture on the water, their accounts are purely anecdotal. For the most part, nobody’s rigorously tracked what’s going on with salmonflies and other stoneflies, caddis or mayflies — even on the country’s most famous trout streams.
But in 2023, the United States Geological Survey and Environmental Protection Agency published a study analyzing nearly three decades of macroinvertebrate data across 6,100 study sites on U.S. waterways. The richness of species diversity declined by more than 23 percent over the study’s timespan. The density of insects dropped by about 7 percent. In short, the study found, bugs are undergoing an alarming and rapid decline across the country. “Without protections for stream communities, especially those in anthropogenically modified habitats,” the authors concluded, “they likely will continue to degrade and perhaps lead to a loss of ecosystem functions and services.”
The study, though, doesn’t speak much to specifics or to the unique factors impacting rivers in the Northern Rockies. While some factors — like rising temperatures — echoed everywhere they looked, urban streams and midwestern rivers laden with runoff from industrial agriculture face very different challenges than, say, the Gallatin or the Upper Snake.
“To know that there is a problem you have to know what things were like before,” MSU professor Lindsey Albertson says. “And unfortunately, our long-term records are not that great.”
On streams throughout the GYE, surveys of these little-loved macroinvertebrates are few and far between. To remedy this, Albertson started monitoring hatches on the Madison and Gallatin a decade ago. That work, she hopes, can help create a baseline of data to help scientists and anglers alike understand what’s happening with the hatch.
In particular, she focuses on salmonflies — both in the field and in the lab. “Even though they’re charismatic and iconic, we actually don’t know a whole lot about them,” she says.
Her studies reveal unique adaptations and point to a major stressor, especially on the Madison: warming water. Although it’s a different watershed, her findings echo Parks’ hunch about the cause of salmonfly decline on the Yellowstone. Salmonflies have a relatively narrow thermal tolerance. When water gets warm enough, they can’t survive at all. But even slightly hotter temperatures breed differences in physiology and behavior, Albertson says. For example, as water heats up, salmonflies do the arthropodic equivalent of push-ups. Getting their reps in helps them stay oxygenated in slightly warmer water. It also requires more energy, and that can take away from energy necessary for essential life functions, like producing eggs.
Albertson’s research shows higher numbers of salmonflies at cooler sites and lower numbers at warmer sites. “So as temperature goes up, salmonfly numbers are lower,” she says. Cooler water, she finds, also breeds larger salmonflies. In water that’s slightly warmer, salmonfly body size is smaller. Even this impact could have big consequences for the ecosystem. For female salmonflies, a smaller body could mean the potential to carry fewer eggs. It’s also a smaller snack for trout and birds. “If you eat one big juicy hamburger,”she says, “that might keep you full longer than eating a bunch of carrot sticks.”
Still, the news isn’t all bad. Over the decade since she began her study, Albertson hasn’t found evidence of major change in salmonfly populations (save for a small but statistically insignificant decline near Ennis). That said, the finding comes with a major caveat: in ecological terms, 10 years is a blink of an eye.
Albertson mustered a way to look at a longer timespan, unearthing a Montana State University graduate student’s work from the 1970s. The student sampled sites downstream of Ennis Lake where, at the time at least, salmonflies were present. Albertson returned to several of his study sites. She couldn’t find a single bug.
That finding matches up with anecdotal accounts of anglers: salmonflies are functionally extinct on the Lower Madison. “There is just no way they play the same role in the ecosystem that they used to,” she says.
Since the 1970s, according to Albertson, salmonflies have lost about 25 percent of their habitat on the Madison River. As the water continues to warm due to climate change, Alberton’s models suggest the bugs will lose an additional 25 percent of their current habitat on the river by 2100. The water will simply be too hot for them.
“To know that there is a problem you have to know what things were like before.”
Lindsey Albertson, ecology professor, montana state university
“The plight of salmonflies is a good representation of the plight of aquatic insects in general,” says Birrell, adding that data show salmonflies have declined or undergone local extinctions in at least 12 blue ribbon and gold metal trout streams nationwide. In some places, like the Logan River in Utah or the Arkansas River in Colorado, they’ve disappeared entirely.
Birrell and his colleagues at The Salmonfly Project, working with local organizations, have started monitoring programs across the West. Like Alberton’s initiatives on the Gallatin and Madison, their goal is to create the data that could contextualize the anecdotes of anglers across the region and pave the way for conservation efforts that could, as his trucker hat professed, “Save the Hatch.” While The Salmonfly Project is named after this single, iconic insect, salmonflies are just their entry point — they monitor for all kinds of bugs, from caddis to mayflies.
There are a few buckets into which pressures on salmonflies and other aquatic insects fall: dewatering, temperature, nutrient loads and sediment, Birrell says. “Aquatic insects are indicators of water quality,” Birrell says. “They are the canary in the current.”
Like Albertson, Birrell says there’s no evidence of a broad bug collapse across the region’s most productive trout streams. “It’s more subtle,” he says. Invertebrate communities are likely quietly, slowly shifting. Species with a higher tolerance for warmer water and pollution flourish, while those that are more sensitive suffer.
Protected by the cold, clean headwaters in and around Yellowstone National Park, local streams are actually better off than many across the country, or even in other parts of Montana. “We have perhaps a little bit more time to protect these areas, to make the changes that will make them the most resilient,” Birrell says. “But if we don’t do anything about it, it’s probably just going to follow the eventual trend.”
Changing bug communities: What can we do?
Connor Parrish, Gallatin Project Manager for Trout Unlimited, overlooks a meadow on the Taylor Fork, a major tributary of the Gallatin River north of West Yellowstone. Parrish is a good friend of mine, and we spent the morning fishing (mostly unsuccessfully) and looking for salmonflies. The high peaks of the Taylor-Hilgard peer down at us in the distance, and the river meanders through a meadow below. To the untrained eye, Parrish says, the place looks absolutely pristine.
But look closer. “You can see the scars on the landscape that still persist,” he says. This stretch of the Taylor Fork has little streamside vegetation. There are few cottonwoods or willows. Those that do exist are small and scraggly. The banksides are sheer and deep. While this looks natural to most passers through, this is the legacy of a lengthy history of use and abuse — and it has big consequences for bugs both in the Taylor Fork and downstream on the Gallatin.
Here, Parrish says, the first major impact came from early fur trappers who removed beavers. Without natural dams holding back the water, the river system had nothing left to constrain the waterway’s energy. Then came agriculture. Cattle tramped through streambeds. They overgrazed. Ranchers drained wetlands and removed riparian vegetation in the name of cow habitat.
As railroads expanded across the West, that development came with a demand for timber for ties. Logging to meet that need took a toll as well. In remote areas like the Taylor Fork, “splash-dam logging” was the easiest way to get timber to market. That meant building huge dams out of logs and letting water back up behind those dams containing thousands of downed trees. Finally, loggers would blow up the structures, unleashing a surge of water and timber downriver. “It made for geologic-scale flooding and erosion events,” Parrish says.
We walk down to the stream. Parrish grabs a fistful of sediment. It’s a soggy mass of tan mud, nearly clay. Then he grabs a fistful of cobbles — perfect habitat for bugs. “What salmonflies and the other macroinvertebrates that we think about in these kinds of systems need is this coarse loose stuff,” he says. All the fine, loose, sticky sediment rushes downstream, packing in gaps between rocks and clogging up habitat. “For bugs, it’s like having less rooms at a hotel to stay at,” he says.
Today, the Taylor Fork also lacks shade from larger vegetation that cools water and the natural dams or woody debris that captures sediment and cool water alike, slowing the flow into the main stem of the Gallatin. He calls it a “double whammy” of warm water and more sediment.
All that sediment is a major source of phosphorus. Low flow, warm temperatures and high loads of both phosphorus and nitrogen have led to severe algal blooms on the river in recent years. The Montana Department of Environmental Quality listed the middle section of the Gallatin — which includes where the Taylor Fork — as “impaired” in 2023.
Here and across the region, the historic scars on this landscape can heal. “A big thing that we could do is just try to reverse all that,” Parrish says. A possible solution sounds simple: Add logs and manmade beaver dam analogs back to the stream at large scale along the Taylor Fork corridor. Reverse-engineering natural river systems means accepting things we collectively often avoid, namely: messiness. A healthy river system is a mosaic. Logjams, woody debris and beaver dams add a beneficial complexity to the system.
Right now, this project is purely hypothetical, a dream of Parrish’s. If it gets realized, he says, the water table could rise higher. Trees and shrubs could grow where now only sparse vegetation flourishes. That could provide the raw material necessary for beavers to naturally recolonize. Slowing flow could also capture sediment that would otherwise rush into the mainstream, clogging up cobbles crucial for insect habitat. Instead of cold water flushing out after runoff or a storm, the new structures in the stream could slow things down. Cooler water could enter the Gallatin later into the summer, providing better habitat for both fish and bugs.
Political will, public buy-in and sheer capital make for immense barriers to realizing a project like this one. Parrish hopes to see it realized by the time he retires (he’s in his late 30s), but time, climate change and the glacial pace of bureaucracy are against him. Getting the work done at the scale necessary — even on this one tributary — would take years of public scoping and millions of dollars. But the technology could be relatively simple: logs and labor.
The Taylor Fork is but one example. Across the GYE, nearly every river and tributary bears its own scars, both past and present. The scope of the work necessary to restore fish and insect communities alike is stupefying.
If the sky is falling — fish and bugs dying, state-mandated closures called Hoot Owls shutting down angling when the water heats up each summer — the picture can seem too dreadful to make a meaningful difference, Birrell says. But the work at The Salmonfly Project and by scientists like Albertson, he contends, could provide the missing link between angler anecdotes and boots-on-the-ground conservation, like Parrish’s dream project on the Taylor Fork.
“The sweet spot between hope and concern is the sweet spot for action.”
Back on the Madison with Birrell, swallows swoop all around us, scooping caddis out of the air. But no fish are rising. Birrell expects us to encounter the very beginnings of the salmonfly hatch. So far today, we’ve only found one schuck, or exoskeleton. In terms of bigger bugs, we’ve mostly found “mutant stoneflies.” Mutants are no X-Men. Anglers gave them the nickname because their wings are malformed and they can’t fly. But the bugs can handle slightly warmer water than their larger, salmonfly brethren. The abundance of mutants here could reflect the subtle ecosystem shifts we’re seeing throughout the region.
“If you care about biodiversity, if you care about birds, if you care about fish, if you care about local fishing industries and economies, the bugs are what’s holding all of it together,” Birrell says. “They’re the nucleus of the ecosystem.”
As we talk, the heat of the summer isn’t yet here, but it’s coming fast. Rivers are dynamic systems; the only thing certain is change.
Birrell talks about bugs with the reverence often reserved for wolves, bears or beavers. “If we want to protect these rivers, these hatches, fishing experiences for generations — we need to pay attention,” he says.
As he finishes his sentence, waxing poetic about the future of the region’s iconic fisheries, Peter Merz, a fishing guide Birrell’s training to survey for insects, chimes in. “Hey!” he says. “We got a salmonfly!”
It’s black and large, almost sluglike, still in its larva stage. Soon, it will crawl its way to the riverbank and hatch. It will unfurl its wings and buzz into the air. It will become part of a feast for birds and trout and a marvel for anglers.
