A killer fungus has been discovered that stops crazy ant spread in its tracks.
By Larry Hodgson
Gardeners in the Gulf States of the US have had (yet another) serious non-native pest on their hands for the last 20 years. The gradual spread of an imported invasive ant known as the tawny crazy ant* (Nylanderia fulva) has been creating havoc for gardeners and farmers.
*It’s also known as the Rasberry crazy ant, for its discoverer, Texas exterminator Tom Rasberry),
Just being in the garden loses lots of its appeal when swarms of crazy ants crawl up your legs and all over your body. And they bite, too (but don’t sting). Their bite is not particularly painful to humans, but does inject formic acid. That causes irritation and leads to itching.
The damage of the tawny crazy ant to the environment is enormous! It has been described as an ecological wrecking ball, driving out native insects and small animals and causing major headaches for homeowners. It damages plants and crops by foraging directly on them looking for sugars, by killing beneficial insects and by spreading and “farming” aphids which suck the sap of plants and weaken them.
Crazy Ants Disrupt the Whole Ecosystem
It also kills baby birds and small mammals and eradicates honeybee colonies. In some areas, crazy ants are so numerous that dogs don’t even want to go outside because they become completely covered in them. Homes have been overrun by ants that swarm breaker boxes, air conditioning units, sewage pumps and other electrical devices, causing shorts and other damage.
The tawny crazy ant likewise tends to wipe out all other ant species in its territory, including that other unwanted invasive species, the fire ant (Solenopsis spp.). That might appear beneficial to gardeners who fail to realize that most ants, although not fire ants, are, in fact, beneficial and even necessary in maintaining a healthy ecosystem.
This yellowish to reddish ant is called the crazy ant because of its erratic behavior and rapid movement. It runs jerkily in every direction about without following established trails like other ants.
Apparently, the tawny crazy ant first arrived in the US in ballast from a ship coming from its native range in northern South America. A specimen showed up in Brownsville, Texas, as long ago as 1938, but, as with many invasive species, there was a lengthy acclimatization period before it began to become a threat.
Environmentalists have only recognized it as a serious problem since 2002, but it now causes damage to farms, gardens and homes in all the Gulf states, from Texas to Florida.
Scientists at the University of Texas at Austin have good news, though. They have demonstrated how to use a naturally occurring fungus to crush local populations of crazy ants. They describe their work in the journal Proceedings of the National Academy of Sciences of March 29, 2022.
“I think it has a lot of potential for the protection of sensitive habitats with endangered species or areas of high conservation value,” said Edward LeBrun, a research scientist with the Texas Invasive Species Research Program at Brackenridge Field Laboratory. He is the lead author of the study.
The Critical Discovery
The idea for using the fungal pathogen came from observing wild populations of crazy ants becoming infected and collapsing without human intervention.
About eight years ago, research scientists Edward LeBrun and Rob Plowes, also with the Texas Invasive Species Research Program, were studying crazy ants collected in Florida. They noticed some had abdomens swollen with fat. When they looked inside their bodies, they found spores from a microsporidian fungus. Microsporidians are a group of fungal pathogens that hijack an insect’s fat cells and turn them into spore factories.
It’s not clear as yet where the unnamed pathogen came from, perhaps from the tawny crazy ants’ native range in South America. Nor how it reached the US. However, it is clearly present and spreading. LeBrun and his colleagues have found the pathogen in crazy ants at sites across Texas and Florida. It reduced all infected populations severely; 62% disappeared entirely.
LeBrun theorizes that crazy ant colonies collapse because the pathogen shortens the lifespan of worker ants, making it hard for a population to survive through winter.
Whatever the reason, it seems to be a crazy-ants-only problem. Unrelated to other microsporidians that infect ants (it’s in its own genus!), the new pathogen doesn’t appear to harm native ants or other arthropods, making it a seemingly ideal biocontrol agent.
Here’s an example of fungus’s effectiveness:
Estero Llano Grande State Park in Weslaco, Texas, was losing its insects, scorpions, snakes, lizards and birds to tawny crazy ants. Baby rabbits were being blinded in their nests by swarms of acid-spewing ants. In 2016, they called in LeBrun and his team.
“They had a crazy ant infestation, and it was apocalyptic, rivers of ants going up and down every tree,” LeBrun said. “I wasn’t really ready to start this as an experimental process, but it’s like, OK, let’s just give it a go.”
Using crazy ants they had collected from other sites already infected with the microsporidian pathogen, the researchers put infected ants in nest boxes near crazy ant nesting sites in the state park. They placed hot dogs around the exit chambers to attract the local ants and merge the two populations.
The experiment worked spectacularly. In the first year, the disease spread to the entire crazy ant population in Estero. Within two years, their numbers plunged. Now, they are nonexistent and native species are returning to the area. The researchers have since eradicated a second crazy ant population at another site in the area of Convict Hill in Austin.
Life for Crazy Ants Won’t Be So Easy in the Future
“This doesn’t mean crazy ants will disappear,” LeBrun said. “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.”
The researchers plan to test their new biocontrol approach this spring in other sensitive Texas habitats infested with crazy ants.
The work was funded by the Lee and Ramona Bass Foundation, Texas Parks and Wildlife Department, the US Fish and Wildlife Service, Travis County Natural Resources Division and Austin Water Wildlands Conservation Division.
Repercussions Around the World
This ant-busting fungus will certainly be commercialized throughout the American Southeast fairly soon. Exterminators may soon be showing up at local homes bearing hot dogs, but this time, not for the family barbecue!
That said, crazy ants were probably never going to be a problem for most home gardeners.
Outside of areas with climates much like the Gulf states, with mild winters and high humidity, they simply don’t survive. Tawny crazy ants are known to have spread to the Caribbean and Australia, for example, but are unlikely to make it to Philadelphia, Toronto, Tokyo or London.
However, if such specific natural biocontrol agents can be found for other invasive species, that may eliminate the majority of chemical pesticide use in agriculture and home gardening.
The information is this article was largely adapted from a press release from UT News.