Photography: John Francis Peters

Bullhead City, Arizona Was a Retiree Paradise. Then Came a Biblical Plague of Flies.

Meet the small, greasy insects upending life in an idyllic community.

WWhen Craig Vallon and his wife Denise moved to Bullhead City, Arizona, in 1973, he thought he was the luckiest man in the world. The two had met as teenagers in the suburbs of Los Angeles. Denise was a party girl, and her wealthy family had hoped she’d settle down with a doctor. But Craig proved irresistible to her: A sportsman with the stature of an NBA player, Craig’s career aspiration was to become a real-life version of his childhood idol, Tarzan.

Like many other residents, the Vallons were lured to this small city on the lower Colorado River by the low cost of living, the nearby casinos, and the outdoors opportunities. Craig and Denise were educators, and Craig liked to give talks costumed as Jedediah Smith, the legendary Mojave mountain man who helped blaze what would become part of the Oregon Trail. After his retirement, Craig enjoyed sitting in the back room of the house, which was stuffed with hunting trophies, and watching the river flow by through floor-to-ceiling windows.

In the spring of 2015, Craig began to notice a few moth-like insects flitting around under the lights outside. They were about the size of houseflies, dull brown in color with long fuzzy wings, big black eyes, and whiplike antennae. With each passing evening, their numbers grew. Soon they became an uncountable mass, a swirling, kinetic cloud that hung over the river’s edge like a new state of matter.

Caddisflies cluster together on a window at Denise Vallon’s home, Bullhead City, AZ.

During the day, the insects would settle on the windows, their grimy black silhouettes marring the view like dead pixels on a television screen. When the flies took flight again, they left behind grease marks on the glass. Denise complained that the swarms were so thick she couldn’t have dinner parties outside. They’d stick to the hamburger patties coming off the grill.

Craig learned that these insect interlopers were caddisflies, a native species that thrived in places with clean, clear water. “Caddis,” as they’re known to anglers, are an important part of the Colorado River ecosystem, serving as food for native fish. Other stretches of the waterway were actually suffering from a dearth of the aquatic insects, and local officials insisted that their abundance in Bullhead was an auspicious sign, an indication of just how healthy the lower Colorado River was. But Craig felt like he was being gaslit, that officials were refusing to acknowledge an insect run amok. “I’m going to expose this thing,” he told Denise. He decided to run an ad on a digital billboard on Highway 95, the main drag into town, that highlighted the crisis and offered an easy solution.

Don’t buy property near river in Bullhead City.
Enjoy the Swarm — You’ll Need a Net

“You’re going to get your ass sued,” Denise told him. Craig paid for the first week, and then his neighbors gave him donations to keep it up for another week. “The city was getting pissed,” Denise remembers. Craig drove around the neighborhood with a stack of flyers that he had her stick in people’s mailboxes — at least until the post office warned them it was a federal offense.

Whatever triggered the outbreak undoubtedly had something to do with the river, where the caddisflies spend most of their lives. The 1,450-mile long Colorado River begins in the Rocky Mountains and quenches much of the thirst of the Southwest before terminating as a trickle into Mexico’s Sea of Cortez. Once a famously muddy river, it has been made crystal clear by over a dozen major dams on its main stem and many more on its tributaries — a transformation that has upended its natural ecology.

Denise Vallon looks out at the Colorado River behind her home, Bullhead City, AZ.

Wild rivers that churn and pulse and rise and fall have become a rarity. Around the world, two-thirds of the longest rivers have been dammed, creating massive man-made reservoirs and halting the flow of critical sediment downstream. Dams have obvious consequences for wildlife: They prevent fish from reaching their spawning grounds and flood former habitats. Environmentalists often decry the loss of species diversity in rivers that have been dammed. But while some species lose when we meddle with rivers, others win, sometimes in dramatic and unforeseen ways.

Craig Vallon passed away last year, but the ecological horror story unfolding in and around Bullhead shows no sign of letting up. To battle the caddisflies, local officials brought in PhD entomologists from across the country, tested out pesticides and deterrents for homeowners, and dumped hungry trout in the river, hoping they’d consume the caddisfly larvae. Now, 2019 marks four years of trying to beat back the infestation, but nothing seems to be working very well.

On TripAdvisor, you can still find reviews of the once-popular riverwalk in Laughlin, Nevada. The titles tell the story: “Attack of the Bugs,” “Bug City,” and “Nice walk if you don’t mind bugs.” One reviewer wrote, “If you’ve ever read Stephen King’s The Mist, you’ll have an idea of what this is like.”

EEarth is in the midst of an unprecedented die-off, one in which a million plant and animal species are poised to be pushed into oblivion, many within the next few decades. But because most of us never see much wildlife anyway, the so-called sixth extinction is relatively easy to ignore in our day-to-day lives.

There’s a flip side of the extinction crisis, however. While most insect species’ numbers are withering under deforestation, pollution, and climate change, some are actually exploding. Certain insects, in particular, are poised to win the ecological lottery, taking advantage of a post-extinction landscape devoid of predators and competitors. That includes invasive species, which humans have spread around the globe, and some native species, which were quietly subsisting in their ecosystems until conditions changed.

Our warming climate, for instance, has contributed to mountain pine beetle populations exploding and expanding into new regions, killing tens of millions of acres of forest in the last couple decades. Meanwhile, silty runoff from farms in Pennsylvania may have contributed to so many mayflies emerging from the Susquehanna River that officials in the town of Wrightsville have to use street sweepers to remove their bodies, and have started turning off the lights on their bridge to prevent accidents.

The Colorado River and Bullhead City, AZ from the Laughlin, NV shore.

Biodiversity is not just about the sheer numbers of species in an ecosystem, but about the relative proportions of the players. Healthy ecosystems have both rare and common species, and periodic population explosions are the norm for species like rats and cockroaches with the ability to multiply quickly. But when a single species becomes overwhelmingly abundant year after year, that’s usually a sign that there’s a serious problem. “Everybody recognizes that there are native species that are breaking out and becoming pests,” says Ruth Hufbauer, an insect ecologist at Colorado State University in Fort Collins.

Dams are one of the most dramatic ways humans have altered the landscape, transforming a free-flowing river into a series of wide, deep lakes. While these changes wipe out some species, they make life easier for others. In the tropics, dams have been linked to booms in populations of mosquitoes carrying malaria. In the Pacific Northwest, dams on the Columbia River have created the perfect island nesting sites for birds known as a Caspian terns, which have doubled in numbers since 1980 and prey on endangered salmon emerging from hatcheries.

The nightmare future of the planet is not just one without pandas and polar bears, but where once diverse ecosystems are turned into monocultures as biologically barren as an Iowa cornfield. Dams can contribute to that transformation. “When dams go in you often get these simplified insect assemblages, where one or two species really dominates,” says Ted Kennedy, an aquatic ecologist with the U.S. Geological Survey in Flagstaff, Arizona.

Arizona’s caddisfly plague can be viewed as a warning of the threats faced by our rivers, and the communities that depend on them. “What can we do to make them go away?” asks Albert Graves, an engineer who once tried to stop caddisflies from taking over a water canal near Phoenix. “The answer is practically nothing.”

DDavis Dam, located just about 90 minutes south of Las Vegas, is a brutal, concrete bulwark as tall as five Walmarts stacked atop one another. When I visited one morning in April, a man stood on the bank casting a fishing line into the reservoir, and a couple peered off the bridge into the dark, still waters below.

This northwestern corner of Arizona was a wasteland when the Utah Construction Company began work in earnest on the Davis Dam in 1946. To house workers, the company established a settlement on the river’s bank. Residents named it Bull’s Head, after a distinctive rock that would eventually be submerged under the dam’s reservoir, Lake Mohave.

Cheap real estate and the lack of property taxes in Bullhead City lured refugees from the southern California sprawl and vacationers seeking some of the best fishing on the Colorado. Striped bass congregated below Davis, fattened by the pulverized fish parts spewing from the hydropower turbines like a smoothie. In 1977, an angler caught a striper weighing 59 pounds and 12 ounces, a freshwater world record that stood for over a decade.

The most common species of caddisflies in Bullhead are known to scientists as Smicridea fasciatella. They hatch out of eggs deposited in the middle of the river and spend most of their months-long lifespan as a kind of underwater caterpillar. With the river rushing above them, caddisfly larvae attach themselves to rocks, building tiny cylinder-shaped retreats out of debris where they feed on passing algae. Entomologists estimate that when the conditions are right, up to 1,400 caddisfly larvae can occupy a single square foot of river bottom. In the final phase of their lives, they construct a cocoon. Then, they sprout wings and emerge from the water to spend their final two weeks on Earth in a frenzied search for a mate.

On my first morning in Bullhead, I met the town’s mayor, Tom Brady, at his office in the brick municipal complex on the south end of town. “I love everything about Bullhead,” Brady began, cheerfully describing the area’s recreational opportunities.

Left: Bullhead City’s mayor, Tom Brady. Right: Rusty Braun shows off a vial of “fish guts” which are said to contain Caddisfly larvae.
Davis Dam.

Over the course of our conversation, though, his tone took a turn. The caddisflies, Brady explained, were just the latest insect plague facing the city. Before the caddis, Bullhead saw a black fly infestation in the 1980s, the first sign that the ecosystem was out of whack. “I honestly believed when I moved here that our town would never grow because the black fly situation was so out of control,” he said. Like caddisflies, black flies are a native species, bloodsuckers whose aquatic larvae also grow up in the river. Brady remembers residents walking their dogs with insect head nets and helplessly waving their arms in front of their face. “The Bullhead salute,” they called it.

Black flies were finally controlled by introducing a strain of bacteria called Bacillus thuringiensis israelensis — Bti, for short — into the river. Bti produces a toxin that kills black fly larvae without making the water undrinkable or harming other creatures. “That has probably been one of the greatest things for Bullhead City’s growth,” Brady says. The city has expanded from a population of 10,700 in 1980 to over 40,000 today. But the Bti toxin is useless against the caddisfly infestation, which threatens to put a damper on the city’s future growth. “It’s a problem, and it could grow worse,” he said.

Although caddisflies don’t bite like black flies, their hairs and scales can send people into coughing and wheezing fits. Some unlucky souls have full-blown allergic responses, developing asthma, hives, and eczema. Befitting a creature that only expects to live a fortnight, their bodies are so mushy that if you try to brush them away, they’ll just smear across your skin and clothing. One angry resident told the town entomologist he had to wrap his kid up in plastic just to walk from the house to the car.

At night, the bugs are attracted to lights, and the riverfront casinos across the river in Laughlin draw them in from miles away. During the day, they hide out in the shade offered by waterfront vegetation and the alleyways between homes. Insecticides sprayed in the air don’t work well at controlling an insect that spends most of its life in the water, and you can’t just dump a poison in a river that’s headed straight for Phoenix. Some residents resort to household chemicals to kill them. “We spray a lot of Windex,” admits Brea Chiodini, who runs a dinner cruise on the Colorado called the Celebration. Others have taken out their frustration by incinerating masses of flies around their homes using handheld blowtorches.

Before the caddisflies came to Bullhead, they started pestering a small unincorporated community below Parker Dam, 88 miles downstream. Biologists caught 3.5 million caddisflies — about 12 pounds worth — there on a single summer night in 1999. Another 15 years would pass before they began laying siege to the more populous city to the north.

Denise Vallon on the shores of the Colorado River.

If there were gradual changes brewing in the ecosystem during that time, it went mostly unnoticed by Bullhead residents. In the spring of 2015, the caddisflies seemed to materialize overnight. They had been around in previous years, but never in such extraordinary numbers and never for such an extended period of time. Had there been just a single caddisfly season each year — as occurs with more northerly species — then life might be bearable. But Smicridea fasciatella can go through at least two generations annually on this stretch of the river, taking to the air from April to June and September to December. Sometimes those two emergences blur together into eight straight months of entomological ickiness.

As word of the infestation has spread, residents fear that home prices on the river will start dropping, and people will start moving away en masse. Then, the town will face another kind of extinction problem. “If you’re trying to sell a home to someone on the river,” says Rusty Braun, who runs a small marina and bait shop, “you’re gonna have to trick ’em.”

YYou wouldn’t know it from a visit to Bullhead’s waterfront, but caddisflies are, in fact, among the most imperiled insects in the world, beaten down by water pollution and farm runoff. A recent study in the journal Biological Conservation reported that 63% of caddisfly species are threatened with extinction. The prospects for other aquatic insects, including mayflies and dragonflies, are nearly as bleak, which doesn’t bode well for all the creatures that depend on them.

And yet there have been a handful of scientific studies from dammed rivers around the world, like missives from the Twilight Zone, where certain species of caddisflies have multiplied to freakish numbers. “The swarms appear as dense plumes of black smoke, which undulate slowly in the breeze,” an entomologist named Calvin Fremling wrote in 1960 about the town of Keokuk, Iowa, on the Mississippi River. “Masses of insects dart into the faces of passersby, flutter under their eye glasses and fly down their open necked clothing.” Similar reports have come from Uji, Japan, and Fort Erie, Ontario. The common variable between all these communities? They are all located just downstream from dams. Years after these dams went up, caddisflies seem to emerge like a phantom of an ecosystem destroyed.

Joe Iburg, Bullhead’s entomologist until a few months ago, says the Colorado River dams have turned the once-sandy river bottom into a giant pile of rocks, giving caddisflies a lot more nooks in which they can build their retreats. Prior to the completion of Glen Canyon Dam in 1963, 91 million tons of sediment flowed down the Colorado River. That number has since dropped to 15 million tons. The dam has upended the biological equilibrium of the river. Stripped of sediment, the river’s water grows clear and still in reservoirs like Lake Mohave, and floating algae have all the sunlight they need to proliferate. For the caddisfly larvae downstream, that translates into a year-round all-you-can-eat buffet.

At the same time, other natural factors that might have kept caddisflies populations in check have also been disrupted. Dragonflies, which are native to this ecosystem and typically eat caddisflies, have become alarmingly rare. Native fish like the razorback sucker, which preyed on caddisflies, were decimated by the construction of the dam. Meanwhile, striped bass, an introduced species, preys on all those smaller fish that might have kept caddisflies in check. Locals say that bats, prolific consumers of flying insects, have also declined in Bullhead. The river had become just as much a desert as the land on either bank.

Denise Vallon’s neighbor uses a blowtorch to kill Caddisflies on the side of his home’s river deck, Bullhead City, AZ.

A lot of people in Bullhead, including Craig Vallon, saw a link between the caddisflies and the partial shutdown of a federal fish hatchery in late 2013 that had stocked the river with hungry rainbow trout. When the caddisflies first became a nuisance in 2015, officials voted to spend their pest control budget buying trout from a hatchery in Colorado. Iburg, however, has found that the trout being stocked just weren’t eating that many caddisflies before they themselves got hooked by fishermen or gulped down by stripers.

A historic attempt to prevent a caddisfly outbreak in Montreal during the 1967 World’s Fair was a failure, even with the help of the now-banned pesticide DDT. To deal with an infestation in a water canal in Scottsdale, Arizona, engineers built a 12-foot-wide steel brush to scrape them off the concrete surface. But the bugs would just reattach downstream. “Most entomologists in the world say there is nothing you can do with caddisflies,” Iburg told me. He gave residents practical advice, like using yellow lightbulbs rather than white ones to make them less attractive to caddisflies, and he launched a new research project just before his departure to see if the pheromones caddisflies use to attract mates could be used in traps.

But Iburg knows that a long-term solution to the caddisfly menace would require a more drastic measure. One possibility was periodically turning off the spigot on the dam: Let the river run dry to scorch all the bugs. It was a kind of check on the system that may have happened naturally in the past during periods of drought. But a dry river is a nonstarter: It would upend the local economy, harm endangered species, upset boaters and farmers, and, at least temporarily, ruin the views of many retirees.

OOur ecosystems have been so altered by humanity that keeping them functional has become a full-time job. Forestry crews now have to do controlled burns to make up for decades of fire mitigation. Beaches have to be artificially replenished with sand because of a combination of sea level rise and all the infrastructure we’ve added to the coast, which alters the natural movement of sediment. New insects are imported into ecosystems to try to control previous invaders. One rogue scientist has even dumped iron in the ocean in the hopes of facilitating a phytoplankton bloom that would suck carbon dioxide out of the atmosphere.

Meanwhile, the wildlife populations that rely on these systems are responding in unpredictable ways. Long before caddisflies began plaguing Bullhead, they became scarce upriver in the Grand Canyon. This too is a man-made disaster: The caddisflies upriver, a different species, lay their eggs on the water’s edge. But because the water levels depend on releases from the Glen Canyon Dam, they fluctuate on an hourly basis, often leaving the eggs high and dry.

Tourists take a morning stroll along the Laughlin River Walk, Laughlin, NV.

The U.S. Bureau of Reclamation has started experimenting with timing water releases from Glen Canyon Dam to help revive the aquatic ecosystem there. They run the river at high flow levels in the hopes of flushing more sediment into the canyon, and then they allow a few days of steady “bug flows” to improve the survival of insect eggs. So far, it seems to be helping. But for how long?

Across the West, dam removal has been championed as a way to reverse the damage we’ve caused to river ecosystems. The writer Edward Abbey once called the Glen Canyon Dam “an insult to God’s Creation” that will one day collapse to the delight of humans and “to other creatures which have an equal right to the enjoyment of the earth.” For now, however, dam removal advocates have gone after dams that have long since outlived their usefulness, and far too many people depend on the dams of the Colorado River for their removal to be taken seriously.

Bullhead City, of course, wouldn’t exist were it not for Davis Dam. For the foreseeable future, its residents will have to adapt to this strange new ecosystem we’ve created — or move away from the river. In the meantime, they’ve hired a new entomologist — or, as the town paper called it, a new “bug slayer” — whose standout resume included caddisfly experience in Nebraska. He is going to need it. After I returned to my home in Los Angeles, I got an email from Denise, letting me know the bug season had arrived. “Caddisflies are in huge swarms and landing all over the windows,” she wrote. “It has just started but I believe it is going to be biblically epic.”

Journalist based in Los Angeles. Working on a book about the coronavirus vaccine race.

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