The first signs of trouble appeared in the summer of 2006. That July, locals began posting queries on fishing blogs, asking about the strange plants they’d seen on the waters hugging the bank at Jeems Bayou, a popular fishing hole on a northern finger of Caddo Lake. A few people guessed duckweed, an invasive species common to swampy wetlands, but others recognized the real danger: giant salvinia, an aquatic fern capable of doubling its biomass in mere days. Scientists call it the world’s worst weed. Caddo residents took to using another description: the lake-eating monster.

Australian researchers have calculated that, given the right conditions, an M&M-size salvinia plant could blanket 39 square miles of water in just over three months. As the advancing front reaches maturity, it swells into a carpet of vegetation up to three feet thick, smothering other life in its path by consuming nutrients and blocking sunlight from penetrating the water below. Fish can’t survive. Native plants and amphibians struggle. Lake recreation halts as viny roots clog boat engines and become ensnared in propeller blades. In some areas, the dense layer of salvinia can even become a substrate for other opportunistic weeds, making it difficult to tell where the lake ends and the shore begins.

Salvinia is bright green and oddly pretty—fuzzy, with small oval leaves. The aquarium and water-garden industries began importing it from Brazil more than three decades ago for use as an ornamental plant. In Texas, it escaped for the first time in 1998, inexplicably appearing in a schoolyard pond in Houston. That year also marked the first invasion into U.S. public waters, at Toledo Bend, a vast reservoir one fourth the size of Rhode Island along Texas’s border with Louisiana. For the next eight years, officials in Texas and Louisiana raced to keep pace with its spread, but in 2006, the plant began hopscotching from lake to lake on the bunks of contaminated boat trailers. It eventually infested almost every freshwater body in Louisiana and about a third of those in the eastern half of Texas.

Salvinia growth over time. Hover over lakes for current salvinia status.

MAP BY DYLAN MORIARTY

Caddo, the largest naturally formed lake in Texas, fell prey early. Straddling the Texas-Louisiana border just north of Interstate 20, it is the only ecosystem in Texas (and one of just 38 in the country) protected under the Ramsar Convention, an international treaty adopted in 1971 to preserve rare wetlands. The Texas side is more flooded forest than lake, and its towering cypress trees, some over three hundred years old, are draped with long Spanish moss. This otherworldly environment has inspired generations of legends. In 2015, Animal Planet dispatched a film crew there in search of Bigfoot. Don Henley, Eagles co-founder and Rock and Roll Hall of Famer, owns property on its shores, and in July he dedicated $100,000 of the proceeds from his concert at American Airlines Center, in Dallas, to the Caddo Lake Institute, which he founded. Every year, thousands of anglers, duck hunters, canoers, kayakers, and camera-wielding tourists flock there.

Australian researchers have calculated that, given the right conditions, an M&M-size salvinia plant could blanket 39 square miles of water in just over three months.

When locals first spotted the salvinia, at Jeems Bayou, on the lake’s Louisiana side, the fish and wildlife departments from Texas and Louisiana teamed up and began to saturate the surging mass with herbicides. Residents, meanwhile, removed what growth they could find. But to no avail. Three months later, a front-page story in the Shreveport Times warned, “Giant salvinia threatens Caddo Lake.” By then, the plant had claimed 250 acres of water. One lakefront property owner, who was trying to clear her shoreline with a kitchen strainer, told the newspaper that the growth “will get so solid that a man can walk on the water.” (Not true, though a toddler could likely pull it off. An herbicide contractor once set a 2.5-gallon jug of chemicals on a mat of salvinia to see if the container would sink. It did not.) Alarmed residents in Texas strung a bright orange barrier two miles across the lake in a desperate attempt to halt the invasion. Each day, volunteers motored out to the fence, scraped it clean with oversized nets, and loaded the captured plants into black garbage bags. This proved somewhat effective until September 2008, when the remnants of Hurricane Ike swept through and destroyed the barricade—and all hopes of containment. By 2013, half the Texas side was covered, including Johnson’s Ranch, the oldest inland marina in the state and the only one on the Texas side with public gas pumps.

Residents have continued to fight back, sometimes in unorthodox ways. Someone once took a 2,000-degree blowtorch to a metal tub full of salvinia. The plant appeared to die, but a week later, green sprouts emerged from the blackened mass. After three weeks, the plant had resurrected itself in full. The state has spent almost $3 million applying herbicides to affected lakes in the past four years, about 40 percent of that on Caddo alone, but the poison must be dispersed repeatedly because the salvinia inevitably rebounds or drifts back into a previously cleared area on breezes and currents.

In recent decades, Caddo has faced a series of assaults, both natural and man-made, including mercury contamination, encroaching water hyacinth, and oil spills. None, however, rival the threat posed by giant salvinia. The ecological and economic damages are mounting, but for those who call the lake home, the stakes are even higher. John Winn, who grew up on the lake and now runs Caddo Outback Backwater Tours, told me, “I would liken it to finding out a good friend of yours has cancer.”

A lane marker in the Big Lake section of Caddo, July 13, 2017.

The plan to enlist an army of insects to save the lake came from Australia. Salvinia had arrived there the same way it had in the U.S.—imported for water gardens before escaping to rivers and lakes and thriving in the sunny climate. For answers on how to stop its spread, researchers from Queensland turned to the plant’s origins. They captured and tested Brazilian weevils: tiny bugs, some two millimeters long, that evolved in their native habitat with an appetite for nothing but salvinia.

In 1981, in the scientific journal Nature, the researchers reported that the weevils were showing spectacular effectiveness on a large test lake, with no damaging side effects (the history of using one nonnative species to fight another is fraught with disaster). The salvinia was eventually contained in much of the country. Similar success stories played out across the world and in parts of the southern U.S. In 2010, scientists from Texas A&M University set up a research station to raise and release weevils at Caddo Lake National Wildlife Refuge, funded largely by grants secured by former U.S. senator Kay Bailey Hutchison. Around Caddo, the weevils soon developed a cultlike following.

In 2013, though, word spread that the A&M research facility was in danger of closing—its backing was drying up—so a band of volunteers from the Greater Caddo Lake Association of Texas got the idea to open a weevil factory and launch their own campaign for salvinia control. Leading this troop of armchair entomologists was an affable exterminator named Daren Horton. Horton, now 57, grew up in the Oak Cliff neighborhood of Dallas, and he later started a pest-control business in the city. After discovering Caddo with his wife, Becki Horton, on a canoeing trip, they started visiting so often that they realized they should up and move there. “The bald cypress trees and the Spanish moss and the way the sun comes through at certain hours and the fog on the water—it’s got to be one of the most beautiful places in the country,” Horton said. They sold their home and business and, in 2008, built a house on Cypress Village Island, a spit of land that juts into the center of the lake. He joined every civic organization that would have him, and he became president of the Greater Caddo Lake Association about the time everyone started talking weevils.

After hearing about the A&M station’s impending closure, Horton’s group scheduled a meeting at a local community center. They expected a smattering of interest. Instead, word of their weevil plans circulated through Facebook posts, and 125 people packed the room. “Fear No Weevil” became their rallying cry. Not everyone was convinced—Are they going to get in my garden and eat my lettuce? How is that little bitty weevil going to take care of all that salvinia?—but they managed to cobble together $200,000. It mostly came from grants and government agencies, but they also collected $14,000 over brisket and coleslaw at a Labor Day picnic. “To have a barbecue cookout and see somebody that you know doesn’t have anything walk up and put in twenty bucks,” Horton said, shaking his head. “It’s mind-blowing that people love the lake that much.”

“To have a barbecue cookout and see somebody that you know doesn’t have anything walk up and put in twenty bucks,” Horton said, shaking his head. “It’s mind-blowing that people love the lake that much.”

Still, their campaign faced a significant obstacle: Caddo’s unfortunate latitude. The bug, like the plant it craves, is tropical. Problem is, weevils are felled by frost, while salvinia can stand slightly lower temperatures. This has proven to be Caddo’s curse, said Julie Nachtrieb, a biologist who raises and studies salvinia weevils at the Lewisville Aquatic Ecosystem Research Facility, part of the U.S. Army Corps of Engineers. In places with mild or even nonexistent winters, weevils can be released a few times and then “you can walk away and let nature take its course,” she said. But at Caddo, the weevil populations must be reconstituted every spring, giving salvinia a running start.

Research efforts are under way to find a heartier weevil. A team led by Louisiana State University, for example, is harvesting and testing salvinia weevils from cooler parts of South America. Earlier this year, in the journal Biological Control, it reported finding weevil populations in Uruguay that could survive freezing temperatures longer than the weevils currently in use (twelve days versus eight, on average). Encouraging, but still years away from rescuing Caddo.

After months of fund-raising, the Greater Caddo Lake Association began construction on its very own climate-controlled weevil-production facility. In August 2014 it hosted a ribbon cutting for the Morley Hudson Weevil Greenhouse, appropriately located in the town of Uncertain. Uncertain is a community of about one hundred, on the lake’s western shore, and perhaps more than that of any other Caddo hamlet, its future hinges on the health of the lake. The building was named for a longtime resident whose family had given generously to the cause, and it was billed as “the first high-production weevil facility in the world.” (I could not verify this but won’t meddle with the bragging rights.)

Now, this summer, three years after opening, the greenhouse faced a crucial test. Winter was mild enough that the weevils had a chance of surviving. Could they beat back the monster before it began flourishing once again in the warmer months?

A small cove with young salvinia beginning to cover the water, July 13, 2017.

On a cloudy morning in June, I meet Horton at the Caddo Lake National Wildlife Refuge, an eight-thousand-acre reserve that was once home to the World War II–era Longhorn Army Ammunition Plant. Horton is accompanied by Tim Bister, a state fisheries biologist, and Robert Speight, a Caddo native who works for the Northeast Texas Municipal Water District. Speight, a large man with a salt-and-pepper beard, wears a T-shirt that says “Weevil Rancher.”

The headquarters of the refuge is a drab forties-era cinder-block building that was last inhabited by Thiokol Corporation, which used it to build rocket motors in the seventies. (The Cold War bomb shelter is still intact.) Room 518, the designated weevil lab, lies at the end of a dim hallway. Here, volunteers conduct a census of weevils grown in the greenhouses. Inside the room, I ask Bister if anyone in Texas has embraced the weevils quite as enthusiastically as the Caddo group. He pauses in thought. “I don’t see anybody else walking around wearing a ‘Weevil Rancher’ shirt,” he says, nodding to Speight.

Speight grew up on the banks of Caddo, in the region known as Pine Island Pond. His dad, a founding member of the Greater Caddo Lake Association, gave him his first johnboat when he was seven years old. Sometimes, when periodic floods rendered roads impassable, Speight would drive his boat across the lake to a friend’s house to catch the school bus. “It would be dark before I got home because I would fish all the way back,” he recalls.

For Speight, who is 53, Caddo still retains its allure. “Ten minutes from leaving the dock, you can be in an area that just looks so totally primitive you wouldn’t know what century you were in, let alone what day of the week it was.” Salvinia has robbed him of the serenity he once found in the quiet backwaters. “All I can think about now when I go out is what salvinia is doing to the lake,” he says. “The inner peace is gone.”

“All I can think about now when I go out is what salvinia is doing to the lake,” he says. “The inner peace is gone.”

We leave the refuge and drive ten minutes north, to Uncertain, where the Shady Glade Cafe advertises a fried baloney sandwich and fries for $6.99. Around the corner lies the weevil greenhouse, and inside its doors are ten shallow tanks, 10 feet wide and up to 27 feet long, filled with giant salvinia. Standing in one of these tanks, scraping muck from the bottom with a hay rake, is Ted Barrow. A former maintenance manager for the postal service, he and his wife retired and moved to the north shore of Caddo ten years ago. They had bought the property as a weekend retreat, in 1996, and then decided it was a place they never wanted to leave. The first summer that salvinia completely stranded their boat dock, they learned weevils were available in Houma, Louisiana, so they loaded 35 plastic containers into an air-conditioned trailer and made the six-hour drive south. They released the bugs on the lake, but nothing happened. Admittedly, he says, they were amateurs.

No longer. Barrow is now the greenhouse’s only hired hand, and he has pledged to keep the facility running until he can be permanently replaced. For him, there is little choice. “I’m very worried,” he says. “If we don’t continue, we’re going to lose this lake.”

So far, the Caddo volunteers have successfully released about 370,000 weevils, but Horton still finds that he has to dispel myths. Some folks expected the weevils to gobble up the plant like miniature Pac-Men immediately after release. “This is a marathon, not a sprint,” he says often. When it comes time to release this batch of bugs, the weevil-laden salvinia will be loaded into 25-gallon plastic bins and ferried onto the lake. Volunteers will dump their cargo over the side of the boat and, Horton says, offer a sort of parental encouragement: to live long and eat well.

Horton is realistic about their prospects. He knows that Caddo is probably stuck with salvinia forever. The plant has now metastasized into every last alcove, despite two state-contracted boats spewing herbicide five days a week. “What we’re hoping for is what they have in Brazil,” he says, “where the salvinia may be there, but the weevils keep it under control.”

A week after my visit to the greenhouse, I travel with a crew of biologists from Texas Parks and Wildlife in a Pro-Drive mud boat engineered to traverse shallow muck. We launch at the state park into Big Cypress Bayou and motor past Big Pines Lodge, the popular restaurant where you could once leave with a bellyful of all-you-can-eat catfish and a brand-new .38 Special (catfish is still on the menu; guns and ammo are not). At a fork in the bayou, we take an abrupt left turn to enter the swamp known as Willowson’s Woodyard.

Willowson’s has long been the most picturesque spot amid a sea of picturesque spots. At its mouth, it spans the width of two football fields, but it gradually narrows as it stretches back more than a mile, and some passages are so thick with cypress they can be navigated only by kayak. As a child of East Texas, I grew up fishing waters like these. My dad would wake me in the Saturday morning darkness so he could launch his two-seat aluminum boat by dawn. With my hook dangling from its red-and-white bobber, I’d watch the sun rise through Caddo’s foggy labyrinths. It seemed primeval—the only place, before or since, where I have seen acre upon acre of lily pads.

Yet as we pull into the cove, I’m stunned by what it has become. The entire expanse, which used to be brown, glassy water, is a virtually impassable meadow of alligator weed and grass. The air has the acrid stench of rot. In a distant corner, I spot a lonely flotilla of lily pads, brown and curling on the edges, trying to hold its own. The bottom layer of vegetation, the raft for this floating horror, is a packed tangle of salvinia.

It’s an encouraging sign, but no one celebrates. Salvinia has proved relentless too many times.

Much of salvinia’s most insidious damage occurs beneath the surface. Whenever the plant dies, after either a winter freeze or an application of herbicide, the mass sinks to the lake bed, depositing silty layers of organic matter more rapidly than natural forces can absorb. The buildup along the bottom depresses water levels, making the lake more shallow and disrupting life for fish like bass and crappie that lay eggs on hard, muddy surfaces. A Louisiana biologist had told me that in salvinia-infested lakes, he’s seen fish nesting on the sides of submerged trees.

As our boat slows to a stop, Thomas Decker, one of the biologists in our group, leans over the side and scoops up a handful of salvinia. Examining the plant, he finds several brown patches, a sign that it is slowly perishing. This site is the main testing ground for the weevils from Uncertain, so it’s an encouraging sign, but no one celebrates. Salvinia has proved relentless too many times.

We make our way out of Willowson’s Woodyard and eventually arrive at Pine Island Pond, the community where Robert Speight spent his youth catching bream. Last November, the area was choked in salvinia. But it was also a spot where state wildlife officials had dispersed weevils, and the biologists with me hope to discover that the insects have persevered through the winter. As we turn into the inlet, we’re astounded to find nothing but open water. We ride farther, past boat docks and rows of cypress and a channel marker that’s become a favorite perch for a great blue heron, and see few signs of growth. Decker scans from shoreline to shoreline in delight. “This is amazing!” he shouts.

We eventually reach a marsh where a stand of trees forms a delicate canopy, and there, hovering around the tapered trunks of cypress, we come upon a thin layer of salvinia. Its density is sparse enough that the plants swirl into lacy patterns of green as the boat passes through. In another context, it would be beautiful. As the biologists dip buckets into the water to search for weevils, I can’t help but wonder if I’m looking at the last gasps of growth at Pine Island Pond or the beginnings of the next onslaught.

Laura Beil is a freelance journalist based in Cedar Hill.