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NOW RELIEF could be on the way.

In 2015, scientists from the UT lab were studying the tawny crazy ant invasion and discovered that a naturally occurring fungus, Myrmecomorba nylanderiae, had infected some colonies in Florida and Texas. Over the next few years, every infected ant population they observed declined, more than half of them disappearing completely.

This fungus is a microsporidian, a group of parasitic fungi that include more than 1,000 species, which can infect a wide variety of hosts. The tiny organisms typically hijack a host’s fat cells and use them to make spores, which are reproductive cells capable of developing into a new fungus. Their method is something out of a sci-fi horror movie: one of the spores produced by the fungi has a filament, a sort of coiled tube with a harpoon tip that it shoots out. When the tip hits a potential host, it penetrates its cell walls. The spores then hijack that cell and take over its normal function, causing it to produce more spores instead.    

The UT scientists — including Edward LeBrun, Rob Plowes and Lawrence Gilbert — began studying several things about the fungus and ants: how the fungus is transmitted through the ant colony, when it is most virulent and how it affects the overall ant population. The team got a call from staff at Estero Llano Grande asking for help, and they decided to conduct a test using the fungus as a method of biocontrol. Biocontrol is using a living agent such as a natural pathogen, or disease-causing agent (in this case the fungus), to control a pest (tawny crazy ants).

This particular pathogen needs a live host, LeBrun points out. That meant the team couldn’t just isolate its spores and create some kind of powder or liquid to apply to ant colonies. Instead, they had to collect live infected ants and introduce them, along with their infection, to uninfected nests.

“Infected populations are perishable fruit,” LeBrun says. “You have to find them and take them to the uninfected nest. It sounds simple and straightforward, but we had a lot of setbacks. We had to learn tricks for how to handle these ants.”

According to behavioral and genetic data, all the tawny crazy ants in the Southeastern U.S. and Texas are members of one super-colony, so the ants recognize each other as close relatives. This recognition is based on smell, LeBrun explains. Individuals can acquire odd environmental odors when handled in a lab, and that can cause a colony to reject introduced ants.

“One approach we developed to get around that problem was to collect nests from the site where we want to introduce the disease, collect some from infested nests and combine the two in buckets in the lab,” LeBrun says. “That essentially forces the introduced ants to integrate with all the odors of the colony host.”

Then they put those ants in nest boxes near colony sites in the park, sweetening the deal with bits of hot dog to lure the local ants out to merge with the infected ones.

Within a year, the fungal disease spread to the entire crazy ant population in Estero Llano Grande, and after two years, the ants disappeared from the park. Native species began returning.

The team eradicated a second crazy ant population at a site in Austin’s Convict Hill area. Then they were asked to come to the rescue at Lost Maples.

The team introduced infected crazy ants to 10 sites at the park in May 2022. Now, they are monitoring the ants to see whether efforts to introduce the disease are working. Those first ants collected by Hannusch in August contained no infected individuals, but LeBrun notes that this is not surprising.

“It can take nine months or a year sometimes before you can detect the disease,” LeBrun says. “It is kind of a depressingly long interval. But there are a lot of ants and it can be hard to find the ones that are infected in such a large population.”

In the ant populations where the infection had occurred naturally, it typically took four years (but sometimes as long as seven years) for an infection to wipe out a colony. LeBrun says it isn’t clear why the population artificially inoculated with the fungus at Estero Llano Grande disappeared in two years.

CHECKING LOST MAPLES

LEBRUN AND HIS colleagues collected and tested a second set of ants from Lost Maples in late November. Out of 50 samples collected at 10 stations, they found two that were positive for the fungus. 

That low number suggests that the infection likely transmitted from the introduced ants to some of the resident nests, LeBrun says.

“We will not know whether the disease has established in the population at Lost Maples until we see whether it overwinters successfully at the site, sometime in June. In low prevalence infections, the pathogen can die out over the winter.”

In that case, it would need to be reintroduced into ant colonies in the park.

The team continues to work on finding a more efficient way to do that. In the meantime, people can help by limiting further spread of the invaders. Tawny crazy ant queens can’t fly, so the only way the ants spread is by hitching a ride. Someone taking a potted plant with a nest fragment to a new location can do the trick, and park visitors can inadvertently spread a colony if ants get in their tents, RVs or other gear. Park visitors should check camping vehicles and equipment before leaving a park and try to sweep or shake out any ants so they don’t get a free ride to a new home.

Hannusch reports seeing less evidence of the ants at Lost Maples in the late fall, which she attributes to their normal response to environmental conditions, including cooler temperatures. With any luck, winter — and the fungus — will be tough on the ants.   

Melissa Gaskell is a science writer based in Austin.