Neutralizing Crazy Ants
Biologist Edward LeBrun is weaponizing a natural pathogen to use as a biocontrol for tawny crazy ants from South America that have become prevalent in the southeastern US.
Over the past 15 years or so, tawny crazy ants from South America have been popping up across the southeastern U.S. like paratroopers dropping in from an invading army. Where they take hold, they're like an ecological wrecking ball and they cause headaches for homeowners. Podcast host Marc Airhart joined biologist Edward LeBrun in the Texas Hill Country to test a new weapon in the battle against the destructive tawny crazy ant.
Edward LeBrun: So a colleague was camping out here and he's an ant biologist and photographer, and he sent me some pictures and said, "Ed, guess what I found?" I would have taken his word for it, but the pictures were obviously it.
Marc Airhart: It's a warm May afternoon in the Texas hill country. I'm walking along a gravel trail in Lost Maples State Natural Area with biologist Edward LeBrun.
EL: I believe that was winter of 2019, is when he contacted me, so I planned to come back in the spring when the ants are more active.
MA: But then the COVID-19 pandemic hit. He had to wait until fall of 2020 to see for himself.
MA: So he was definitely right?
EL: Oh yeah, they were everywhere. They're mainly in the drainages … right up along the creek.
MA: He's talking about tawny crazy ants, an invasive ant from South America. Over the past 15 years or so, they've been popping up across the southeastern U.S. like paratroopers dropping in from an invading army. Where they take hold, they wipe out most of the native insects and other small invertebrates. That has ripple effects, especially for birds which rely on insects to raise their chicks. Crazy ants also cause a lot of damage in homes, where they swarm inside walls and short out electrical equipment. Here in Lost Maples, the tree-lined canyons of the Sabinal River and Can Creek provide the perfect habitat for tawny crazy ants. So it's not too surprising that this is one of the newest fronts in the ongoing invasion.
EL: Presumably it got here in an RV. So anywhere you've got folks taking RVs to go camping, if they live in environments with crazy ants, the crazy ants will move into their RVs and then they'll move out when they're camping. In my experience, that's how most state parks get these ants.
MA: I'm Marc Airhart and this is Point of Discovery. Edward LeBrun studies invasive species at the University of Texas at Austin's Brackenridge Field Laboratory, which is part of the growing Texas Field Station Network — a base from which scientists and students can team up to learn about how to protect unique natural resources in Texas. We're here on a stealth mission: to test a new weapon in the battle against the destructive tawny crazy ant.
MA: Now I'm not a biologist, so ants are pretty much ants to me. But as we're walking along, we notice a thick trail of ants crossing our path near the water.
EL: There's crazy ants for you, there's a nice trail …
MA: You didn't have to bend down to tell these are crazy ants, what's the tip off?
EL: I know where I am, for one thing.
MA: If I saw ants from 5 feet away, I'd just say those are some ants.
EL: It's the uniform size, the body size in general, you get an eye for it, the coloration, so there's this red-brown color, a tawny color, butterscotch is actually what the name refers to. … This large trail is another tip off …
MA: … but the "crazy" part, where does that come from?
EL: It has to do with their foraging biology. When they're foraging for resources, they do a lot of turning, so on that trail, you saw they were just walking straight along the trial, but when they're looking for food, they'll be spread out and do a lot of high angle turns as they move, it looks like a lot of random movement patterns. That's where the name came from.
MA: So now I know what the enemy looks like. It's time to engage in some biowarfare. A few years ago, LeBrun and his colleagues discovered a kind of fungus that naturally infects some populations of crazy ants. When it's present, the ant populations slowly decline and, in some cases, disappear altogether. He's been working for the past few years to weaponize this natural pathogen and use it as a biocontrol agent.
MA: Okay, so what have we got in the truck that we're taking out?
EL: We're taking out some 5-gallon orange buckets from Home Depot, Homer buckets that have screened lids on them, and inside of them are nests of tawny crazy ants … and it's mostly rotten wood that the ants are nesting in.
MA: Two weeks ago, he came here to Lost Maples and collected crazy ants from five nests around the park and put them in these buckets. He brought them back to his lab in Austin and added other crazy ants that are already infected with the fungus.
EL: … and then we are going to go return them to the nests from which we collected them and there will be great homecoming celebrations.
MA: It's like Thanksgiving break when college students go home to see the family and bring back a cold virus, which everyone in the whole house catches.
MA: This is one of two methods LeBrun is trying in Lost Maples to wipe out the crazy ants. He's already tested a simpler version where he took some infected ants from another site hours away and dropped them off in the park. This time, we're testing a more complicated version of the same idea—where ants from Lost Maples are brought to the lab in Austin, spend a couple of weeks with infected ants, and then come back to Lost Maples. LeBrun wants to see which method has the greatest impact.
MA: So you hope they work equally as well, just one is simpler?
EL: Yes, exactly, hopefully there won't be any difference and we'll never do this again! Because it's a lot of work.
MA: Well, I'm glad I could be here on a 95-degree day doing the complicated version with you.
EL: Exactly, walking ¾ of a kilometer carrying heavy buckets full of dead wood and ants …
MA: For science …
EL: … for science!
MA: And so we tromp along the trail for a while, until his GPS receiver tells us we're close to the first site … and then we veer off into an area around a big tree with rocky ground and patches of leaves and logs.
EL: Gals, you're home. The blue lid is what we're returning, but now we're going to have to find the nest. So we'll have to sort of turn over wood and rocks. …
MA: LeBrun is looking for the telltale signs of a robust crazy ant colony—lots of female workers, just like the ones he's infected, and plenty of babies, or "brood."
EL: Ah, here we go. Ugh! Is that big enough? Here's a nest, a big rock here we've turned over. You can see a bunch of ants, some are carrying brood. Some are carrying a pupa, that little white blob. And there'll all down nesting in this crack in the soil and you can see there's quite a bit of brood in this crack. So this would potentially be a good spot to return them. Before we do it, let's just look a little more and see if we can find anything better than that.
MA: He's looking for the biggest nest he can find to return the bucket full of infected ants.
EL: And here is another nest, but how big is it? … They're down in this dense leaf litter and they're inside this log, in pretty good numbers, but I'm still not convinced, haven't sold me yet. We'll keep looking …
MA: So far, after a few minutes, he's found a pretty good rock with an active crazy ant nest under it—and a log that's just okay.
EL: Alright. So here we have a third nest. Um. They're in here, but …
MA: Mostly just in the wood?
EL: Yeah, and I'm not seeing a lot of brood. I saw the most brood by that rock. So we're going to go ahead and do that rock. … Alright gals, this is where you're going. … get out of there. Let them know when you're home.
MA: He dumps big chunks of wood and thousands of ants and brood onto the nest. And then he covers them up with a big rock.
MA: Give them a little shade?
EL: Yeah. Make them happy. And that's done. Alright. One down, four to go.
MA: After he finishes these "inoculations," it's going to be a long waiting game to see the impact of the infecting fungus.
EL: And what happens next is super variable, honestly. It may just take and spread like a wildfire. We've had it take in a nest and within a year of inoculation the entire population's infected with the disease. And we've also experienced where we do the inoculation and it takes and spreads, but at a much more moderate pace. We don't understand that difference yet.
MA: Even when it does work, it can take several years to dramatically cut down crazy ant populations.
EL: Not a quick fix. But a sustainable fix that doesn't require continual use of pesticides. You know, once you've got the disease established, it's on a trajectory where the ants are going to be suppressed below the point of causing environmental or ecological harm. It's just a matter of waiting.
MA: Back at the campsite the next morning, I ask him how this experimental treatment of the invasive species compares to other, more established biocontrol methods.
EL: It takes a couple of years for it to become prevalent throughout the system. But then once it does, the populations just … it's a ratchet to extinction. I mean, they just keep declining year after year until they're gone. And that's not something we see really with many other biological control programs, ants or otherwise. It's not … a typical outcome.
MA: I remember writing about LeBrun's crazy ant research about seven years ago and the mood was definitely different. It was like: These ants are unstoppable. They're going to swallow a quarter of the country.
EL: And so you go from a future scenario where the whole Southeast United States is covered with tawny crazy ants, like it is covered with red imported fire ants, to a scenario where you have these populations occurring, blinking, growing and dying, and that process just happening over time, over the landscape and never… coalescing, never leading to sort of large scale geographic impacts that … seemed inevitable. … That's a very different, much more positive framework. And now, we also have figured out how to use that tool to, have that disease, to accelerate this ongoing process ... So that's also really satisfying. … this isn't going to be the cataclysmic invasion that we thought it was at one point and that we have a way of addressing important environments.
MA: Special thanks today to Edward LeBrun for letting me tag along on this field trip. Despite hours and hours on our feet for two days in hot weather carrying buckets, it was delightful tromping around in the shaded canyons of Lost Maples with a biologist. He kept stopping to figure out which bird was making that unusual call or to ID some insect. In a shallow pool of water, we found colorful leeches about the size of my pinkie finger, flat and green with orange and black dots on their backs. Ravens croaked their raspy calls from high above us. More than once, we nearly ran smack into a giant spider sitting in the middle of a web stretched across the trail. (That's why I always led him go first.) There's so much life here, so much I wouldn't have even noticed. With a bit of luck, and a big boost from science, hopefully this delicate web of life will remain long after the crazy ants have come and gone.
MA: That's our show. Point of Discovery is a production of The University of Texas at Austin's College of Natural Sciences and is a part of the Texas Podcast Network. The opinions expressed in this podcast represent the views of the hosts, and not of The University of Texas at Austin. Our website is at pointofdiscovery.org. There you'll find videos and links to more resources about tawny crazy ants.
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