The world’s oldest winged insect is in trouble. How frightened should we be?

It moved slowly up and down with what seemed to be the rhythm of a gentle song, its long body and tails hanging below the wings. I was reminded of something I couldn’t quite recall. UFOs came to mind. Then ballet dancers. And finally sprites. I had seen mayflies plenty of times over the years — trout love to eat mayflies, and I love to catch trout — but this one was enchanting.

In the spirit of the moment, I tried to summon what I knew about them. This mayfly had lived for a year or so underwater as a nymph with gills and an outer skeleton of armor. It had probably emerged into the terrestrial world that morning with new wings. It was in search of a mate and didn’t have a moment to lose: In a day or two it would be dead.

When we think about the environment, we tend to think big. As in air, ocean, rainforest and the globe itself. The same holds true about species in peril. Whales, elephants, California condors and other large animals get a lot of press. But insects? Unless they’re the darlings of the bug world — think honeybees and monarch butterflies — they’re pests to be avoided. “It’s really hard to get people to care about an insect,” says Richard Knecht, a paleobiologist at Harvard University’s Museum of Comparative Zoology. “People say, ‘Well, what’s that got to do with me?’ ”

When it comes to the mayfly, I have learned that the answer is: more than you might imagine. Mayflies are a mainstay of the world’s many food chains. The nymphs consume algae, plant matter and decaying leaves. The nutrients and energy gained as a nymph are passed on to other animals when they are eaten by such predators as trout, bass, spiders, frogs, lizards, birds, bats and myriad other animals. Even some people eat mayflies.

Mayflies require relatively cool, clean water to live, which makes them among nature’s best ecological sentinels. For those who know how to look, their bodies hold precise clues about the state of the water and land around them. Some scientists call them “biosensors.” Overly warm water, pesticides, silty runoff from development and other pollution will wipe them out or force them to move to cleaner environs.

In other words, these little-known creatures are invaluable narrators of environmental change. They are also, unfortunately, victims of the very trends they can identify — and they are now fading at a disturbing pace from freshwater streams, rivers and lakes around the world.

Mayflies are the oldest surviving winged insects on the planet. Knecht discovered a mayfly impression from some 300 million years ago in rock behind a strip mall in Massachusetts. The bug’s short-lived elegance has inspired wonder and rumination by artists and poets since the first reference to them in the Epic of Gilgamesh, a Mesopotamian poem and one of the world’s oldest pieces of literature. In an allusion to its brief life span, Aristotle dubbed the insect ephemeron. The Chinese scholar and poet Su Shih used the idea as a metaphor. “We exist no longer than mayflies between Heaven and Earth,” he wrote in 1082. Near the peak of the Renaissance, Albrecht Dürer made an engraving called “The Holy Family With the Mayfly.” The insect is sitting at the feet of the Virgin Mary.

Today, more than 3,700 species live worldwide in freshwater creeks, rivers, ponds and lakes. That includes hundreds of species from Maine to Louisiana to Washington state. I’d heard that a species of tiny mayfly inhabits a creek near my home in Arlington County, Va. I wanted to see for myself. The creek, Pimmit Run, is part of a storm-water drainage network with natural-looking stretches punctuated by concrete tunnels. I arranged my visit at the end of April to coincide with an effort by local citizen-science volunteers to help the county assess the stream’s water quality. The continued presence of mayflies would be a good sign.

Under the direction of a county water specialist, Lily Whitesell, the volunteers worked in pairs, walking in the creek, kicking up rocks and sifting the water with hand nets. Whitesell suggested I look at one of the nymphs they had captured through a field microscope set up on a card table near the creek. I laughed out loud when it came into focus: It was horrific-looking, a veritable sci-fi movie monster with claws, bulging eyes and long, thrashing tails. “Isn’t that cool?” Whitesell said.

When such nymphs transform and take flight, they can offer a great spectacle for people who happen to be near the right water at the right time. Clouds of them hover and bob in the air as they search for mates. The spectacle can verge on the sublime.

Some of the biggest hatches involve Hexagenia, a genus of large mayflies that burrow in silt and mud and in summer erupt from big lakes like Erie and rivers such as the upper Mississippi, Ohio and Illinois. Billions of bugs have emerged in a single day, enough to feed tens of millions of birds. So many Hexagenia have fallen dead in some hatches that municipalities have used snowplows to clear them off roads.

In the mid-20th century, at a time when industrial activity sometimes poisoned lakes and rivers where Hexagenia live, their numbers plummeted in the Great Lakes region. Eventually, clean water legislation curbed much of the pollution, spurring a decades-long rebound in Hexagenia populations.

In recent years, however, scientists and conservationists have been troubled by anecdotal reports that Hexagenia hatches were tailing off again. Roadways did not need plowing as often. And car windshields — an informal measure of upper Midwestern bug life — regularly appeared to be less splattered.

No one had enough data to say for sure what was going on, and there were not enough funds or biologists to test all the water where Hexagenia live. But a few scientists had a clever idea: Perhaps they could use weather radar to see if Hexagenia clouds showed up. The technology had been used to track migrating birds. Why not Hexagenia? When they ran tests of the radar at night, the researchers realized they could see and record images of Hexagenia. They also could use the method to examine how the images of hatches now compare to those previously recorded by weather radar. “The real beauty of it is you can look at patterns through time to see if there have been changes in the timing and the amount of those clouds of insects,” Sally Entrekin, an entomologist at Virginia Tech and one of the researchers, told me.

In 2020, Entrekin, meteorologist and ecologist Phillip Stepanian and four other scientists published startling findings in the Proceedings of the National Academy of Sciences. Year after year, the size of Hexagenia hatches was dropping. The fact that Hexagenia are thought to be among the most resilient of mayflies made the insight especially troubling.

Some scientists contend that the Hexagenia decline may be part of a natural cycle that has been occurring for thousands of years. In any event, they say there are not enough long-term data to make sweeping pronouncements. But Entrekin and her colleagues argue that the evidence points to something ominous. “[P]ersistent environmental changes could threaten to once more extirpate Hexagenia mayflies from North America’s largest waterways, making this ephemeral spectacle — and its vital ecological functions — a thing of the past,” their paper said.

The evidence compiled by the researchers suggests the main culprits behind the Hexagenia decline are humans: our pesticides; the way we treat our sewage; the fertilizers we use on crops and lawns; how we build and spread. The byproducts of so much of what we do leaches into freshwater and fouls it. “There’s no doubt,” Entrekin told me, “that we’re losing the habitat that supports a lot of species that have very narrow environmental requirements.”

It is impossible to draw definitive conclusions about what this means on a planetary scale. The Hexagenia research applies only to one region of America and one type of large mayfly. But the evidence of a global problem for mayflies — and other insects — is mounting.

In the United Kingdom, for instance, a nonprofit group called WildFish Conservation examined chalk streams from 2015 to 2017, and again last year. Such streams can be some of the purest waterways on the planet. They are fed by cool springs that bubble up from aquifers through a form of limestone called chalk, and they’re often home for pollution- and temperature-sensitive insects and fish such as trout. WildFish estimates that the diversity of mayfly species in the streams has declined by as much as 44 percent since 1998. The researchers believe that sewage runoff, silt and a “poisonous cocktail” of pesticides and other chemicals are disrupting these once pristine habitats.

“Mayflies are reliable ‘canaries in the coal mines’ for freshwater systems,” says biologist David Wagner. “And their future prospects, especially in areas that are drying or warming, are bleak.”

I reached out to David Wagner, a biologist and lepidopterist at the University of Connecticut, for context, thinking that perhaps the problems were isolated or overblown. He has studied insects for decades and reviewed numerous scientific studies about them from around the globe. He did not provide much comfort. There’s a growing body of research suggesting that the world is in the midst of its sixth mass extinction, he said. The losses of all kinds of creatures appear to be driven by climate change, habitat degradation, pollution and other ecological stressors.

In a paper for the Proceedings of the National Academy of Sciences last year, “Insect Decline in the Anthropocene: Death by a Thousand Cuts,” Wagner and several other scientists delivered a stark warning about the disappearance of insects. The report did not focus on mayflies, but Wagner told me they are among the most vulnerable of the world’s insects because of their need for clean, well-oxygenated water. “Mayflies are reliable ‘canaries in the coal mines’ for freshwater systems,” he explained. “And their future prospects, especially in areas that are drying or warming, are bleak.”

I wanted to hear from a true obsessive, someone who has built his life around mayflies. So I went to Indiana and connected with Luke Jacobus, an associate professor of biology at Indiana University-Purdue University Columbus and a visiting scholar at Purdue. He has spent his adult life exploring mayflies and runs Mayfly Central, an online clearinghouse of mayfly names and classifications.

I found him near a parking lot on Purdue’s campus, a little more than an hour northwest of Indianapolis. He took me to a basement warren in one of the science buildings and then into a room with concrete floors, painted cinder-block walls and rows of tall metal file cabinets. This was the modest home to a great treasure trove, perhaps the world’s largest collection of mayflies. Jacobus opened some of the cabinets. They were filled with clip-top canning jars. In the jars were vials, and in the vials were mayflies pickled in ethanol, nearly 700,000 of them. “Most of the world’s diversity is here,” he said.

The specimens hold untold secrets about the environment, world ecology and aquatic life. But because there likely will never be enough biologists to study them properly, many of those secrets will never be revealed. Mayflies and fieldwork are going out of fashion for young scientists, who are focusing more on genetics and molecular biology, Jacobus said. Many of those who know how to look beneath the surface sheen of water, who understand the aquatic habitats, anatomy and taxonomy of these tiny creatures, are retiring or dying. “I’m one of the last of my kind,” he explained.

His zeal for the bug was triggered in the winter of his freshman year at Purdue, when he was required to collect an aquatic insect for a biology class. On a lark, he looked in a drainage ditch on his parents’ Indiana farm. He had seen the water many times without paying attention. It was a revelation. “It’s amazing to me that there is so much life and so many interesting things that are in plain sight that we never notice,” he said. “I wound up falling in love with mayflies.” One measure of his devotion: Jacobus and his wife went on a mayfly collection tour for their honeymoon.

Indiana is home to one of the most diverse arrays of mayfly species west of the Appalachian Mountains, about 160 identified so far. According to state records, nearly a quarter of those are threatened, endangered or gone. In some streams in the state and across North America, mayfly populations are so depleted that they may not be able to reproduce in sufficient numbers for much longer. Jacobus calls these bugs “the living dead.”

The next morning, he retrieved me in his pickup truck, and we hustled toward the confluence of the East and West Forks of the White River, about 120 miles southwest of Indianapolis. The target of our field trip was Maccaffertium meririvulanum, also known as the fresh flat-headed mayfly. It was one of those thought to be endangered. Jacobus had received a small research grant to see if he could determine the fate of the species and several others on a state list of missing and endangered species.

As we passed by scrubby fields and small towns, Jacobus riffed on and on about mayflies. He explained that they are so evolved for mating that they don’t eat after they enter the terrestrial world. Their adult mouths don’t even work. He also told me there was no way to understand their fate without a grasp of ecology, the study of how organisms relate to one another and their physical environments.

There’s no global explanation for the disappearance of mayfly populations. The reasons are usually connected to the area around particular streams and lakes — and may include agriculture, construction, suburban runoff, and rising air and water temperatures. But more and more, such environmental stressors appear to be having broader impacts.

He believes that some mayflies will survive, no matter what insults come their way. The heartiest, and, in an evolutionary sense, luckiest, will probably live on after humans are long gone. But he admits that a decline in the variety of species would be a gloomy prospect. When mayflies go missing, he said, it’s a clear indication that yet another place in the world is out of balance.

Jacobus turned the truck into a grassy area near the river. As he gathered his net from the truck’s bed and tucked collection vials into his vest, a man in a pickup truck drove up rapidly. The man lowered his window and said we were on private property and needed to leave. Jacobus was calm. He explained who he was and why we were there. The driver grinned and gave us a why-didn’t-you-say-so look.

He got out of the truck and offered his hand. His name was Lowell. He described himself as a disabled former farmer. It turns out that he was enraptured by bugs. “I’ve been collecting insects since my daughter was born, and she’s 18,” he said. “You can look at God’s personality by looking at the bugs.”

The role of the mayfly in fly-fishing fits what scientists term “cultural services.” That’s the aesthetic, spiritual and recreational value that various organisms provide to the well-being of people.

Jacobus and I walked through some trees and sidestepped down a steep bank to the river. He plunged a canvas-and-mesh pouch on a long pole into the water and muck below. It came out with a splash. He put the mesh bottom close to his face and murmured at the minute bugs wiggling in the reddish silt. Then he scrunched his eyes, as though perplexed. Jacobus said a few of them could be the ones he was looking for. It would take time in the lab, looking at them under his microscope, to be sure. Jacobus was hopeful they would turn out to be the right species — partly for personal reasons but mainly, he said, because he wanted to establish with scientific precision the species that are, and are not, disappearing from Indiana waters.

On the drive home, Jacobus became philosophical. “Mayflies are the oldest group of winged insects still alive on our planet, and they’ve got stories to tell,” he said. “I’m trying to help tell those stories.”

When it comes to storytelling, some of the best practitioners on the planet happen to be fly fishers — who are also fussy, opinionated and more than a little crazy when it comes to trout and mayflies. Anglers and their fishing associations have been keeping a close watch on freshwater streams in America for a century or more. Groups like Trout Unlimited spend millions every year trying to preserve them.

Many fly fishers are worried. That includes Steve Schmidt, who owns a fly shop in Salt Lake City and is a former guide and something of a legend among certain anglers in the West. I called him to talk about Baetis, among the most common groups of mayflies in North America.

We met on a rocky stretch of the lower Provo River, in a Wasatch Mountains canyon east of Salt Lake. Baetis, sometimes called blue-winged olives, or BWOs, are treasured by anglers because they are so common and, like other mayflies, often entice trout to feed on the surface. They live in most streams where there are trout — and in many like Pimmit Run that are too degraded for the fish but healthy enough to support some aquatic invertebrates. They can emerge so prolifically that trout will eat them with abandon while ignoring the fake flies that anglers offer.

With our waders on, we strung up our rods and tied on tiny barbed fake BWOs that were about half the length of a pinkie fingernail. Schmidt had a task for us before the fishing began. He unfurled a large homemade seine net made of mesh attached to four-foot-long dowel rods. He told me to press the rods into the bottom of the stream while he shuffled toward me, kicking up silt and rocks and the aquatic insects among them.

After we lifted the seine from the water, Schmidt found bugs in the dark brown silt that had stuck to the mesh. He plucked them out with tweezers and put them in a plastic container holding river water. Blue-winged olives wiggled like miniature minnows among the golden stoneflies, aquatic beetles and other insects.

The haul showed the lower Provo was very healthy. Other rivers in Utah — and across the West — are not. Drought, rising temperatures and wildfires, coupled with pesticide runoff and silt, have diminished or destroyed freshwater streams here and across the country in recent years. Schmidt believes the populations of mayflies, stoneflies, caddis flies and other aquatic species beloved by anglers are hitting a “tipping point” in many places. And it’s happening at a time when there are more anglers than ever before — in part because so many people thought of fly-fishing as a safe outside activity during the pandemic. “We used to see caddis flies to the extent in the evening you’d get vertigo,” he said of one nearby river. “There were so many flying upstream in this continuous wave that if you didn’t stop looking at them, literally, they would give you the heebie-jeebies.” Schmidt paused. Now, he said, “they’re all but gone.”

Anglers have been driven to distraction by mayflies and other insects for hundreds of years. The first known description of artificial fishing flies comes from a Roman named Claudius Aelianus. In the second century, Aelianus described how anglers on a river in Macedonia tied red wool and rooster feathers to a hook to catch fish. It may be the first description of a mayfly pattern, or so said fly-fishing historian Paul Schullery when I asked him about it.

Fly-fishing as we know it evolved in England in the mid-1800s. By the end of the century, wealthy British men had developed rigid codes for the right way to tie flies and cast to fish on their beloved private chalk streams. When it came to mayflies, these patrician anglers were only concerned with imitating the bugs in their late, doomed hours. To fish for trout with flies imitating underwater nymphs — a routine practice now — was thought dishonorable.

The role of the mayfly in fly-fishing fits what Jacobus and other scientists term “cultural services.” That’s the aesthetic, spiritual and recreational value that various organisms provide to the well-being of people. The more I looked, the deeper the current of mayfly culture went. Consider the British musician Paul Weller, founder of bands the Jam and the Style Council, who wrote a wistful song titled “Mayfly” not long ago: Oh, endless sleep / Perchance to dream / As a mayfly.

An angler and photographer named Ted Fauceglia told me he shot some 25,000 close-up film photographs of the bugs over two decades. He can’t explain exactly why. “I wanted to get the essence of mayflies,” said Fauceglia, who eventually published some of the mayfly photos in fishing magazines and as a coffee-table book. “But they’re a mystery, and I couldn’t put it into words.”

And there’s the Midwestern artist, printmaker and poet Gaylord Schanilec, who spent four years studying mayflies from Wisconsin waters and making wood engravings of them. His devotion to mayflies began one afternoon while fishing. When he saw one rise from the stream, he followed it and grabbed it with his hand. He examined it under a magnifier he uses for engraving. “I was amazed by what I saw: the hues vivid and fresh, the patterns evolving and converging — here was the perfect subject for a color wood engraving,” he wrote later.

Mayfly identification is exacting, so he sought help from a Wisconsin entomologist named Clarke Garry. Their 2005 book, “Mayflies of the Driftless Region,” is a hybrid of art, homage and science. Schanilec told me he was exploring a big question: What does it mean to be alive? “The mayfly,” he said, “really is a pretty obvious example of how fleeting everything is.”

Garry said the project gave him a chance to put his love of science to use in the cause of art. He’s alarmed by what the disappearance of mayflies and other aquatic insects may be telling us. “We’re taking bits and pieces away from the natural world that we may never be able to replace,” he said. “As ecologists like to say: How many rivets can you take out of an airplane before it finally can’t fly?”

In late July the biennial meeting of the International Conference on Ephemeroptera was held virtually for the first time. The conference was convened jointly with the International Symposium on Plecoptera, a group devoted to stoneflies and, as far as I could tell, every bit as committed in its efforts to understand that bug’s place in the world’s troubled environment. Mayflies and stoneflies often coexist in freshwater habitats, and the fate of the two seem entwined.

While most presentations explored aspects of the biology of mayflies and stoneflies, some sounded alarms about places where the bugs were disappearing. Conference organizer Ed DeWalt and another scientist from the University of Illinois, through work with computer models, concluded that certain species could disappear in the Midwest because of development, pesticide runoff and the region’s changing climate. Apparently, Illinois has already lost more than 1 of 4 native stonefly species. Meanwhile, a scientist from India said deforestation, development and climate change in the Western Ghats mountains are imperiling dozens of mayfly species and the freshwater they inhabit.

One study in the conference concerned the upland summer mayfly in the United Kingdom. Craig Macadam of Buglife, a conservation nonprofit at the University of Stirling in Scotland, has studied the bug for years. It’s the only Arctic mountain mayfly in the British Isles. A decade ago, he predicted it would be forced to move north because of rising water temperatures. And now it’s happening. Upland summer mayflies are moving to smaller, colder streams higher in the hills. The species no longer inhabits 4 out of 5 sites where Macadam found them in the past. The outlook for them is grim.

Macadam and several other scientists met with me in a session arranged by DeWalt. Macadam described a citizen-science project that documented a sharp decline of all insects, including mayflies, in recent decades. Volunteers working with his group photographed their license plates before and after trips. The plates serve as a standardized way to measure the number of splattered bugs of all kinds in particular times and places. Macadam said there’s been a 59 percent drop in insect splats measured since 2004.

But it’s his research on the upland summer mayfly that troubles him most. “The species I’ve been studying for over a decade now is disappearing,” he said. “And that makes me incredibly sad.”

Jacobus, the Indiana biologist, was on the video call. In an email exchange later, I asked for his impressions. He was uneasy. “We are losing mayflies and other things that support life as we know it and that make life worth living,” he said. “Nature’s foundations are buckling under global change. The world has always been changing, and it always will, but now it’s changing fast.”

Robert O’Harrow Jr. is a Washington Post contributing writer.