Millions of invasive crazy ants took over parts of Texas and binded baby rabbits by spewing acid in their faces.
The swarms of tawny crazy ants were so intense in some parts of the state, one scientist studying the invasion said scenes were "apocalyptic," with "rivers of ants" going up and down every tree in the area.
Tawny crazy ants (Nylanderia fulva) is a species of ant native to South America.
It arrived in the southern states in the last two decades with the first sample found in Houston in 2002. Since then, infestations have occurred in all Gulf coast counties, reaching as far west as Hill Country, Texas.
Individual infestations can be enormous, with extremely dense populations spanning for miles. Their arrival can be catastrophic for native species, with insects, reptiles and mammals all badly affected by their presence.
In Estero Llano Grande State Park in Weslaco in 2016, park officials noticed an absence of scorpions, snakes and lizards normally found there.
Then, they started finding baby rabbits that had been blinded with formic acid sprayed by the ants.
Edward LeBrun, a research scientist at the Brackenridge Field Laboratory, University of Texas, Austin, who studies tawny crazy ants, told Newsweek: "Rabbits are born in burrows under the ground and I expect that these burrows are very hospitable for crazy ants. In these environments, when tawny crazy ants are at high densities, every suitable nest site is occupied, so I expect the crazy ants move in and simply swarm the rabbits. They spray acid when they fight."
LeBrun had been studying tawny crazy ants when he noticed how some wild populations would collapse without any human intervention.
When he and his colleagues examined the carcasses, they discovered the ant abdomens had become swollen. Further investigations showed they had been infected by a never-before-seen fungal pathogen that turned the ant's fat cells into spores.
"These are intracellular pathogens that hijack their host cells and all the energy the host cells have to replicate themselves," LeBrun said. "Eventually this overwhelms the host. The spores are shed when the ant defecates and spores that are inside the body cavity, like in the fat cells, once the ant dies, these are released into the environment."
The deadly pathogen, Myrmecomorba nylanderiae, was tracked by LeBrun and colleagues in 15 crazy ant populations over nine years, with the team looking at infection levels and abundance of ants.
The team found that once introduced, the fungus would cause the population to decline rapidly and go extinct within four to seven years.
At Estero Llano Grande State Park, the infestation was so bad that the team decided to artificially introduce the pathogen in the hope it would eradicate the invasive ants.
"They had a crazy ant infestation, and it was apocalyptic, rivers of ants going up and down every tree," LeBrun said in a statement. "I wasn't really ready to start this as an experimental process, but it's like, OK, let's just give it a go."
He told Newsweek that before they deployed the fungus, his biggest concern was that the pathogen would impact other species related to the host—in this case native ant populations. They had tested these native species for potential impacts and found there were no infections.
The team found that after introducing the pathogen, infection levels rose extremely fast and the population went extinct within two years. The team believes the infected ants were not able to survive long enough to sustain brood production.
Their findings are published in PNAS. Other native species did not appear to be affected by the pathogen.
After successfully eradicating crazy ants from Estero, the team killed off another population in Convict Hill in Austin.
"I think it has a lot of potential for the protection of sensitive habitats with endangered species or areas of high conservation value," LeBrun said in a statement.
"This doesn't mean crazy ants will disappear. It's impossible to predict how long it will take for the lightning bolt to strike and the pathogen to infect any one crazy ant population. But it's a big relief because it means these populations appear to have a lifespan."
This article has been updated to include quotes from Edward LeBrun.
