The teeming masses of crazy ants descended on Estero Llano Grande State Park and World Birding Center in 2014. Long, brown drifts of them would pile up on the paved walkways alongside buildings in the park, which is just outside the Rio Grande Valley border town of Weslaco. The ants moved in great pulsing streams up and down the park’s trees. They crawled into electric meters and air conditioning units, short-circuiting them, and eventually spread across nearly every inch of Estero Llano Grande’s 230 acres. The insects displaced native species and generally wreaked havoc. When groups of schoolchildren visited the park, staff members taught them the “crazy ant stomp,” which everyone performed to pound their legs free of the skittering pests. Unlike its better-known cousin, the fire ant, a crazy ant does not have a painful sting or bite—but it does cause distress by swarming in large numbers on people’s bodies.
Javier de León, a young biologist who’d recently been transferred to the park and promoted to superintendent, had heard of crazy ant infestations in and around Houston, and he knew what their presence could portend. Scientists had noted that the species was spreading rapidly across the state, disabling electronics and crawling all over frightened people, pets, and farm animals. “It was scary,” he says. Especially because the park, which opened in 2006 as a natural oasis in the Rio Grande Valley, had become a beloved destination not only for locals, but also for bird-watchers from around the world. Visitors to Estero could spot some 340 species of birds, including the raucous chachalaca and the garishly colored green jay. De León worried that the ant infestation could threaten these and other vulnerable species.
In 2016, as crazy ants continued to expand their territory, a desperate Texas Parks and Wildlife Department official contacted Edward LeBrun, an ant ecologist at the University of Texas at Austin. LeBrun and his team had recently published a paper on the species, and the TPWD staff asked the scientists for help. It turned out LeBrun and Robert Plowes, his colleague at the Invasive Species Research Program at Brackenridge Field Laboratory, had just made a remarkable discovery. Their team had found a fungal pathogen that seemed like it might be the crazy ant’s kryptonite. It appeared that this microsporidian pathogen could enter the ant’s cells and replicate. Within a couple of years, the whole colony might be wiped out. LeBrun didn’t think he was quite ready to test that hypothesis in the field, though. “It was in the planning stages, and I was thinking, ‘Well, maybe next year we’ll get on this,’ ” he says. Nonetheless, he drove to the park. The severity of the infestation he saw there led him to change course: “It was apocalyptic.”
He learned that crazy ants had seemingly wiped out some species in the park already. A favorite activity among visitors was a bimonthly nighttime hike, in which participants would set out upon the trails after sundown to identify scorpions. The arachnids glowed bright green under black-light flashlights. Before the crazy ants arrived, de León says, they’d identify seventy to one hundred scorpions per hike. But the ants crowded out the scorpions, which soon disappeared from Estero Llano Grande. “We went from one hundred two years before to zero [by 2016],” de León says.
Spiders, snakes, and countless other critters had also been overwhelmed by the crazy ants, and the birds were next. Park officials found nests where baby birds had been swarmed and blinded by the acid that crazy ants discharge from their abdomens. One video from a wildlife camera showed a white-tipped dove inadvertently pushing a nestling out of a tree while trying in vain to remove the ants from its nest. Park staff even found a few dead baby chachalacas on the ground, overrun by crazy ants. It was clear that the park was under attack.
Due to what they deemed “an emergency situation,” the UT team went to work. Researchers attempted to infect the crazy ant colony by introducing individual ants that already carried the contagious pathogen. It worked: within two years, the park’s crazy ants were eradicated, and LeBrun’s team began testing the procedure on other colonies in Texas.
LeBrun’s work at Estero Llano Grande, alongside years of other research, is documented in a new paper published this week. In addition to identifying the fungal pathogen’s potent effect on crazy ant populations around Texas, the paper also describes two cases (one of which is Estero Llano Grande) in which researchers applied this knowledge to eradicate once-thriving crazy ant colonies. It’s long been suspected that pathogens could have this effect on invasive insects, but according to the study’s authors, this may be the first time anyone has identified the cause and described instances of “population collapse in an invasive social insect.”
A native of South America, the tawny crazy ant made its first Texas appearance in 2002. It’s also called the Rasberry crazy ant in honor of Tom Rasberry, a pest control expert from Pearland, who first spotted the insects at a chemical plant in Pasadena. The species, which likely came to the U.S. as a stowaway on a shipping vessel, swiftly took hold of the Gulf Coast. Unlike some other ant species, which build mounds, crazy ants are opportunistic nesters: they move into preexisting crevices and set up camp, dispersing widely. Rasberry, noticing how quickly and thoroughly these pests gripped an infected area, sounded the alarm. He pored over academic articles, contacted state and federal officials, and spoke about crazy ants with any media outlet that would listen. Crazy ants “probably will be the worst insect that we’ve ever had to deal with in this part of the United States,” he told Texas Country Reporter in 2010. “I don’t know whether I’ve soiled my family name or brought prestige to it,” the exterminator quipped. But the prognosis was grim: “At this point, I don’t see a happy ending,” Rasberry said.
LeBrun took the crazy ant problem seriously. Attempting to better understand the critter, he traveled to its native South America. In Argentina, he observed crazy ant populations that seemed to be kept in check by the presence of other ants and insects. LeBrun wondered: was natural competition the only thing keeping populations under control in South America, or was there something else?
Around 2014, LeBrun and Plowes were studying samples of crazy ants that had been collected in Florida. They noticed the ants’ abdomens were swollen with fat. Inspecting the bugs closely, they discovered spores from the microsporidian group of fungal pathogens, which attack an insect’s fat cells and ultimately kill the insect. Researchers don’t know where this pathogen originated, but they speculate that, like the ant, it could be from South America.
Equipped with this new knowledge, LeBrun’s team headed into the field and began to notice the pathogen in ant colonies around Texas. They found that the pathogen seemed to decimate crazy ant colonies without any human intervention. The researchers were initially cautious. “What we have learned from decades of work with fire ants is that no single organism will be a silver bullet,” Plowes said at the time. “Long-term control of invasive ant populations will depend on a cocktail of host-specific pathogens and parasites.”
But as they continued to monitor crazy ants in Texas, LeBrun and his team observed that within a couple of years of the fungal pathogen’s arrival, the affected colonies became dramatically depleted, and 62 percent of them were completely wiped out. Though the pathogen is naturally occurring, LeBrun’s team realized that in select instances (such as at Estero Llano Grande), they could introduce infected ants to other colonies and bring about a population collapse. Remembering his team’s conservative prediction, LeBrun says that when it came to insects like the crazy ant, everything he’d studied had taught him that no single line of attack could take down a species this pervasive. He’s now happy to admit he was wrong: “This turned out to be a silver bullet.”
Importantly, the pathogen seems to only affect crazy ants, leaving alone other insects, including those native to the region. And while this news will assuage the concerns of those who feared the crazy ant problem would spiral out of control, LeBrun emphasizes that the discovery doesn’t mean crazy ants will immediately disappear from Texas. (The pathogen can’t be bottled and sold as pesticide, and when scientists do introduce it to sensitive ecosystems, its effects usually take a couple of years to unfold.) It does, however, mean the teeming colonies have limited life spans.
When I reached Rasberry by phone, he hadn’t yet heard this news, but he had begun to notice the same phenomenon LeBrun’s team saw: a colony would expand at an exponential rate, then seemingly hit a tipping point at which it would begin to precipitously decline. “All of a sudden, the colonies would just crash,” he told me. Crazy ants are still popping up in the Houston area, but not nearly on the same scale as a decade ago. “Quite frankly, I’m pretty good at knocking out a population,” Rasberry says. He’s still concerned about the damage the ants can do to local ecosystems, but he’s heartened by the recent progress. “Like Mother Nature does,” Rasberry says. “She corrects the problems.”
Back at Estero Llano Grande, Javier de León can breathe a sigh of relief. LeBrun’s team still monitors the area regularly, and as far as de León knows, crazy ants have been completely eradicated. He’s grateful that “the park is being repopulated by critters.” There has been one possible long-term casualty: a tiny brown bird called the northern beardless tyrannulet. Park staff members haven’t spotted the species since the crazy ants moved in, but they still hold out hope. De León was elated when he saw harvester ants move back in. “Thankfully, it is a happy ending,” he says.
LeBrun points out that invasive species are part of the natural order. “As long as there’s been a planet Earth, there have been invasive species,” he says. “It’s just a naturally infrequent process.” Human activity, he says, is to blame for increasing the spread of invasive species to ecologically unhealthy levels. Meanwhile, he’s developed a sense of awe and admiration for crazy ants. When he traveled to Argentina to study crazy ants in their natural environment, LeBrun watched them perform an impressive fighting ritual, which he described as a kind of “stylized combat.” Two ants enter into a standoff until one picks up the other and carries it around as if trying to get it out the nest. “It’s a way of sorting out things like territorial disputes without both sides suffering huge costs,” LeBrun explains. “There’s always things like that that make you admire the organism you’re studying.” Still, he says he won’t shed a tear for the vast armies of crazy ants that will succumb to the pathogen in the coming years.
