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Ants Go Marching

More than an expert traveler, the fire ant is the ultimate invader.

Five World War II bombers took off from a Florida airfield on Oct. 5, 1967 to bomb the American South. An article that ran that morning in the Sarasota Herald-Tribune said that three B-17s and two PV-2s laden with 10,000 pounds of death-dealing cargo each would carry out their missions “with the City of Sarasota and eastern Manatee as their targets.”

While the bombers were certainly at war, they weren’t dropping explosives. Their enemy was a millimeters-long, brownish-red insect known to scientists as Solenopsis invicta, meaning “invincible ant,” and to lay people as the fire ant, aka “ants from hell” and “them devils.” The bombers were to unload mirex, a poison usually applied to grits, onto the critter.

By the late 1960s, the fire ant had been in the American South for more than 30 years. Southerners spoke of ruined crops, destroyed wildlife, and the ants’ fiery sting. How much damage the ants had actually caused was uncertain, but it was enough for the U.S. Department of Agriculture (USDA) to declare war on the pest. During an 11-year campaign, more than 143 million pounds of mirex1 were dropped across 77,220 square miles of land from Texas to Florida, costing close to $200 million. The outcome? The ants nearly doubled their range. The mirex, which was later found to be a carcinogen, persisted in the environment for decades, accumulating in birds’ eggs, mammals’ milk, and human tissues. The world’s leading ant researcher, E.O. Wilson, dubbed the mirex program the “Vietnam of entomology.”

Today, if you draw a line from Virginia Beach to Nashville to Abilene in west Texas, you’ll find fire ants everywhere below it, as well as in Southern California.2 The ants’ annual impact on the economy, environment, and quality of life in the United States totals $6 billion, according to entomologists at Texas A&M University. In Texas alone they rack up $1.2 billion each year: $47 million at golf courses; $64 million at cemeteries (the ants love the open and slightly overgrown habitat around tombs); and as much as $255 million in the cattle industry. They cause other problems too. In Virginia Beach, 30-year-old former marine Bradley Johnson was stung by fire ants while working outside—and died of anaphylactic shock. On at least one occasion, fire ants invaded an elementary school in Tennessee to get candy stashed in kids’ lockers. At Greystone Retirement Community in Huntsville, Ala., a staffer found 79-year-old Lucille Devers3 covered in fire ants, which were crawling from her mouth, nose, ears, and hair: The ants frequently enter nursing homes, attracted by crumbs left in residents’ beds. And scientists anticipate that the ants will keep expanding their range. Climate change and crossbreeding with species more tolerant of cold may enable them to settle farther north.

I, on the contrary, moved south. Last August, my girlfriend, Karen, and I sold most of our belongings, piled two cats, a terrier, and a pudgy brown Chihuahua named Jazzy-B, into a minivan and drove from New York City to New Orleans. A few weeks later, we toasted our arrival with a picnic in City Park. As we rolled up our blanket, our legs suddenly caught fire. Under the glow of a streetlight, we slipped off our pants to find our legs crawling with ants. I received more than 200 stings, which formed welts the size of drink coasters, and my ears and throat swelled up. Half a dozen Benadryls later I was fine, except for hundreds of very itchy pustules. Luckily I wasn’t anaphylactic, but between 0.5 and 5 percent of the U.S. population is.4 For the most allergic, such stings can cause spasms of the bronchial muscles or coronary arteries, preventing oxygen from entering the bloodstream and causing death within minutes. When a few weeks later Jazzy-B stepped on an ant mound and howled, spending the rest of the day licking his paw, I was ready to declare my own war on the fire ant. But first I had to research my enemy.

The range of Solenopsis invicta covers a vast wetland in southern Brazil and Paraguay known as the Pantanal. Sometime in the early 1930s the ants stowed away in coffee sacks, soil, or hollow logs piled in the bottom of a cargo ship. The voyagers were probably just a handful of queens, each about the width of a thumbnail. They ate what they could find down in the hold—cockroaches, beetles, sugary cargo, and, when the pickings got slim, themselves, digesting their own wing muscles and fat reserves. Their ship may well have steamed past Rio de Janeiro, the mouth of the Amazon, and the lush peaks of the Antilles, all while their first batch of eggs gestated in their abdomens. In Mobile, Ala., the ship docked, the sacks or soil or logs were unloaded, and the queens disembarked. Beneath the port’s loading cranes and circling seagulls, perhaps in a patch of newly cut grass, the ants established their first colony: a mound of soil honeycombed with chambers and tunnels that ran as much as four feet deep. They like to build mounds in disturbed habitats such as the edge of a road, the side of a building, pastures, lawns, or near a busy port.5 They eat pretty much anything—seeds, nectar, worms, weevils, butterflies, and even baby sea turtles, snakes, and alligators—catching the young as they hatch.

Colonies consist of queens, workers, and sexuals, also called alates. Queens lay eggs that hatch into larvae—tiny, white, ricelike kernels that develop into adult ants. Alates are born at the end of winter or the beginning of spring, and spend their lives fattening up and preparing for their mating flight. Workers begin life as nurses, grooming and feeding the brood and the queen. They move on to tasks like nest maintenance and sanitation. In their golden years, workers become foragers, handling the colony’s most dangerous job, as it exposes them to predators and the elements. As the life in them winds down, workers act as their own pallbearers, lying down to die in a mass ant grave called the refuse pile.

To trace the ants’ seemingly unstoppable march through the South, I decided to follow their path from where they first staked their claim to American soil. Just before I left, as if an ominous sign from some myrmecological god, a mound swelled up in our backyard. I headed out on my odyssey nonetheless, undaunted.

As the life in them winds down, workers act as their own pallbearers, lying down to die in a mass ant grave.

Mobile, the twelfth largest port in the nation, which last year handled 26 million tons of cargo, greeted me with loading cranes that looked like characters from some gigantic industrial alphabet, a stench of diesel fuel, sea spray that hung in the air, and—sure enough—fire ant mounds. Near the port, cattails poked out the top of one. Its surface was lifeless, but when I kicked it lightly, seeking revenge for my itchy pustules, the creatures swarmed out. They might have been the great-great-great-great-great-great-great-great-great-great-great-grandchildren (queens live about seven years) of the group that had steamed here from South America back in the 1930s.

A short walk from the port was a neighborhood of arching oaks and trim ranch homes with well-clipped lawns. I stopped at 550 Charleston Street, the childhood home of E.O. Wilson—to ponder the fact that the planet’s most famous ant biologist grew up at the epicenter of the planet’s most famous ant invasion. In the weedy vacant lot next door, a young Wilson studied beetles, butterflies, spiders, and all manner of ants, including Solenopsis invicta, whose mound he first discovered in May 1942, at age 12. “I still remember the species I found, in vivid detail,” Wilson wrote in Naturalist, a book about his insect-happy childhood. Now the neighborhood appeared to be fire ant-less—thanks to the tireless, creative, and brutal efforts of its human inhabitants.

Sitting next to a table that held a rifle and a dead squirrel, Lonnie Rayford, a 72-year-old farmer, told me he “done got bit” many a time. In his opinion, one science does not really confirm, just plain grits were good enough to kill the pests. “Dig a hole and put grits in there, they gonna take it down to the bottom and give it to the queen,” he said. “Them grits will kill them.” Down the street, a husky man pulling weeds from his garden told me he used poison.

From Mobile, I headed northeast to Montgomery, where I drove by the state capitol, a creamy white dome calling to mind a magnificent wedding cake. I stopped at Dixie Hardware to learn about fire ant control from the pros. A bearded worker named John showed me to aisle nine, which was an exterminator’s nirvana.

“You got roach and ant killer, you got ant killer, you got Ant Max—it’s some kind of trap,” he said, holding up a rectangular red-and-yellow box that looked like it could have contained movie theater candies, except for a drawing of a vicious fire ant on the side. The best seller was a big orange bag that read “Spectracide Fire Ant Killer Mound Destroyer.”

John’s coworker Richard explained to me the challenges and intricacies of mass insecticide. The problem with poison was that ants often simply moved into the neighbor’s yard, requiring neighborhood-wide poisoning efforts—in other words, it took a village to rid itself of the pests. Another trick involved two people shoveling ants from separate mounds into one another—according to Richard, the ants will assassinate the foreign queens. And then there is gasoline, apparently Alabama’s preferred eradication method. “Take a broom handle, stick it down the mound, pour gas on it, and I know it’s gonna burn whatever is in there,” Richard said excitedly.

Eliminating fire ants seemed a bit like making cornbread; every Southerner had his own favorite recipe. By this time, my welts were long gone and I began to feel bad for the little ants. Especially since I understood that their inexorable spread was, in large part, our own fault.

Naturally, ants don’t really spread that fast: During the 1930s and 1940s fire ants migrated out from Mobile at the rate of about 4 to 5 miles a year, a distance thought to be covered mostly in mating flights. On warm days following soaking spring or summer rains, alates exit the mound surrounded by a gang of worker bodyguards and launch into the air to mate—which they do in large clouds called mating swarms. Males inject females with a lifetime supply of sperm and then die. Newly mated queens land, kick off their wings, and scurry away to start new colonies, avoiding predators like dragonflies, which love to gobble their sperm-filled abdomens. Queens typically fly a few miles during mating flights, and if the wind is right, they can fly more than ten. But that’s it.

Ants can also move when disturbed. In such a case an entire colony moves, but typically only a few feet, a migration initiated automatically by the workers. And a good many fire ant colonies across the South—known as polygyne colonies, meaning those with more than one queen—can actually move without mating flights, by budding off like yeast. A queen and some workers will simply wander off to start a new colony, but, again, they won’t go far. The most successful means for fire ant migration, however, is us. Humans.

Eliminating fire ants seemed a bit like making cornbread; every Southerner had his own favorite recipe.

In 1949 fire ants were mostly situated in a roughly 50-mile-wide radius around Mobile and in a few spots in central Alabama and Mississippi. But as Americans moved to the suburbs during the 1950s, desirous of white picket fences, front lawns, and ornamental shrubs, the nursery trade boomed. Soil, plants, and pots were shipped across states and counties. Hidden in the dirt caked on a bulldozer, in the root ball of a nursery plant, or in the bed of a pickup truck, a newly mated queen can travel hundreds of miles. Thanks to our horticultural aspirations, by 1957 S. invicta were in every Southern state except Kentucky and the Virginias.

It was around then that the U.S. Department of Agriculture set out to eliminate the invaders.6 In 1958 it established a quarantine that restricted the shipment of soil, nursery plants, and baled hay from areas infested with fire ants to those without, unless the products were first treated with insecticides. Between 1957 and 1962 the USDA coated 2.5 million acres with clay granules containing the insecticide heptachlor. It did indeed kill fire ants, but also blackbirds, quail, geese, frogs, dogs, cats, crabs, and millions of fish—a famous fiasco that helped inspire Rachel Carson’s Silent Spring. Few at the USDA seemed to heed her warning, so the war continued. That entomological Vietnam, which lasted from 1964 to 1975, according to The Fire Ants, a book by myrmecologist Walter Tschinkel, left 24 to 33 percent of Southerners with mirex in their body tissues.

Meanwhile, the invincible creatures nearly doubled their range, and some scientists speculated the insecticide was the cause. The poison often eliminated all the ant species where it was applied, giving S. invicta, which is thought to be a better colony founder, a chance to become the dominant type upon recolonization. The secrets of their survival are not entirely known, but Tschinkel thinks it has something to do with large colonies, large numbers of alates, large dispersal distances, and a long mating flight season.

The fire ant front line runs through the middle of Tennessee. I continued north on the ants’ path and pulled off the highway in McMinnville, the heart of the state’s nursery industry and just inside the line. Here, nursery growers have to douse plants’ roots, where newly mated queens sometimes cling undetected, with Chlorpyrifos, a toxic and expensive insecticide. Tommy Boyd, co-owner of Boyd & Boyd Nursery, told me his workers did the task while wearing gloves and respirators. He refused to touch the stuff himself because the insecticide gave him horrible headaches. “I don’t want to die over some chemical,” Boyd told me.

I drove down a windy lane a short time later that brought me to Tennessee State University’s Otis L. Floyd Nursery Research Center. Here I spoke with a gentle entomologist in a flannel shirt named Jason Oliver, who works on a less destructive and more natural ant eradication method: A project to introduce phorid flies, who prey on the ants back in Pantanal. In the late 1990s USDA researchers went to South America to capture different species of phorid flies, which they studied at an Animal and Plant Health Inspection Service (APHIS) lab in Gainesville, Fla., to determine the best one to introduce to various parts of the American South. Oliver’s phorid flies are shipped from the lab to be released in Tennessee.

Phorids lay their eggs in the fire ants’ thorax, and when the eggs hatch, the ants’ heads fall off.7 Oliver showed me a video he had filmed in a petri dish, a fly implanting eggs in an ant. A tiny dot buzzed about some ants; in the blink of an eye it brushed one of them, then continued flying. In that moment the fly had injected the eggs. It happened so quickly I asked Oliver to replay the video. It seemed like a perfect solution. But as impressive as the tiny fly was, it wasn’t going to decapitate a whole colony, just make ants more scared to leave their nests. “We’re always going to have fire ants,” Oliver told me. “There is no way to eliminate them.”

Weaving through rolling hills dotted with nurseries, I drove northwest from McMinnville, skirting the S. invicta front line: To the south, elementary schools, nursing homes, and greenhouses were being invaded, while to the north, the land was, supposedly, fire ant-free. The road took me through the area inundated in the catastrophic floods of May 2010. In Nashville, the Cumberland River rose 33 feet, flooding much of the city, including the Country Music Hall of Fame, the Grand Ole Opry House, and an untold number of fire ant mounds. Contrary to expectations, the ants didn’t drown. Instead, they metastasized further.

The ants would have been well prepared, Louisiana State University entomologist Linda Hooper-Bui explained to me. In their homeland the Pantanal floods happen annually, so they learned to raft. As waters rise, ants evacuate lower tunnels and move higher in their mound, eventually gathering on top. Using hooks, called tarsi, on the tips of their legs, ants latch onto one another and create rafts. Late-stage larvae are covered in hook-like hairs that trap air, encasing them in bubbles. Worker ants stack these larvae three to five thick, forming pontoons that keep the rafts afloat. They place the queen in the middle with pupae and early-stage larvae, which don’t have the crucial hairs to form the bubbles. Save the clumps of eggs workers carry in their jaws and a small amount of liquid food stored in their bodies that will last only a few days, the ants bring nothing aboard. Moreover, as the raft sets off, tipped into the water by the workers, they fling male alates overboard. If the raft is afloat longer than four days, the ants will begin to eat the brood—although not the ones used to make the raft. Rafts can hold together for as long as 21 days, surely long enough to survive the swollen Cumberland River.

Or at least this is what Steve Powell, an entomologist with the state of Tennessee, believes. In February of this year he received a call reporting fire ants in Cumberland City, a remote town about 80 miles north from Nashville and far above the front line. “There’s no rhyme or reason why they should be there, so far from other fire ant infestations,” Powell said. “If I had to guess, I’d say it was the flood.”

Phorids lay their eggs in the fire ants’ thorax, and when the eggs hatch, the ants’ heads fall off.

Continuing my journey, I drove farther north into Cumberland City—a ramshackle collection of vine-ensnarled clapboard homes and shuttered storefronts on steep forested hills above the Cumberland River. On the edge of town sat a massive Tennessee Valley Authority coal plant with four 1,000-foot-tall smokestacks, some of the largest on earth. Beside the plant was a small restaurant with foggy windows, where farmers in overalls sat at low tables gobbling catfish and pork chops. I was looking for someone to speak with about the ants, expecting a thrilling validation of Powell’s rafting theory. Instead I found an unsurprising surprise: Bailey Gafford, a weatherworn cattle farmer in mud-splattered boots, told me fire ants had been in Cumberland City since before the floods. He even suggested an innovative method of eradication I hadn’t heard before: “Put snuff around the mound. They come out and you set ’em on fire.”

On my way out of Cumberland City I stopped at a Civil War cemetery, where wildflowers cloaked weather-beaten tombs and atop a small hill stood a dozen crude cabins, campground for a long-forgotten battle. Our own battle against the ant was still in full swing, however, and it didn’t look like we were winning. The war on S. invicta suddenly fit into a broader picture, that of the Insecticide-Military-Industrial Complex. It was around the time that President Obama announced, concerning the nation’s ongoing war on terrorism, that we cannot remain on “a perpetual wartime footing.” The statement also seemed to apply to our war against the fire ants.

Besides, no matter how we perfect our tactics, these ultimate invaders seem to find new ways to advance. Somehow, Solenopsis invicta crossbred with Solenopsis richteri, another species that came from Pantanal by cargo ship8 to Mobile, in 1918. Originally S. invicta drove out S. richteri, a less aggressive variety that prefers cooler weather and might have found the South too hot. But in the 1980s a hybrid of the two was discovered. No one knows exactly how the hybridization occurred—in certain parts of the Pantanal the two species’ territories overlap, but they don’t interbreed. Here they do, which is perhaps the most ominous sign. Purebred S. invicta don’t survive more than three or four days in temperatures below freezing. Neither does S. richteri. But the hybrid survives freezing temperatures better than either pure species, according to a 2002 study in Environmental Entomology.

Could a hybrid—or perhaps a hybrid of a hybrid—one day push that front line farther north, to Washington D.C., and Philadelphia? What about New York City, with its 8 million residents as clueless as I once was? Recently the ants were brought by ship from the U.S. to Australia and also Taiwan; from there they invaded China. According to a 2004 paper in Biological Invasions, fire ants could potentially infest France, Italy, Greece, Japan, South Korea, Mexico, Central America, and large parts of Africa and India. Is there a way for us to coexist with the creatures? I was still hopeful.

Upon returning to New Orleans I discovered the fire ant mound in our backyard had quadrupled in size. It now towered above the grass blades like Kilimanjaro. As I stood dumbfounded, contemplating what to do, a potato bug ascended the northern flank, an agile alpinist indeed, somehow not inducing a swarm. I wanted to be like the potato bug and coexist with the mound, dance my fingers upon its slopes without getting stung, but I knew it was impossible. Even if Karen and I somehow avoided the nest, there were our animals to think of—the cats, the terrier, and Jazzy-B, who at that moment was watching me from inside with curious dog eyes. Last time he got off easy, but if he received hundreds of stings, the poison would surely overwhelm his little Chihuahua system. The choice was clear. I would have to eradicate the mound.

The abundance of killing choices was what puzzled me: Pit rival colonies against each other, grits, gasoline, a broom and gasoline, poison and, if poison, which one? In the end I decided on a less ecologically invasive technique no one had mentioned except for Oliver—he muttered it under his breath toward the end of our conversation as if revealing a secret that embarrassed him: hot water. Ant Max and Spectracide Fire Ant Killer Mound Destroyer don’t seem to want you to know about it.

I wanted to be like the potato bug and coexist with the mound, dance my fingers upon its slopes without getting stung.

With Jazzy-B and all the others safely inside, I emptied the cat litter box, dusted it with baby powder so the ants couldn’t crawl up the sides, and shoveled the mound into it, quickly adding boiling water to fill it. A second pot of boiling water went into the open mound, to seep down into the interior tunnels and chambers, and then a third and a fourth, too, just to be sure I got the queen. There was an initial explosion of red, with numerous of the brood being moved about, but the water cooked them instantly and, within the hour, the mound was dead.

I gathered my household armor and walked back toward the house, with far from a satisfying sense of achievement. I might have won this battle, but we were still losing the war. Inevitably, another mound would pop up. My “victory” was just a reprieve.


Justin Nobel’s stories about science and culture have appeared in Popular Mechanics, Orion, and Tin House. For his book, Standing Still in a Concrete Jungle, Justin spent extended periods of time in iconic New York City spots observing minutiae. He’s presently working on a book about forgotten small towns of the American South.

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