'Crazy Ants' Spreading In The Southeastern US

In parts of the southeastern US, aggressive fire ants have been driven out by an even more recent arrival, the tawny crazy ant. Edward LeBrun, a researcher at the University of Texas at Austin, describes the newcomers and how one invasive species can out-invade another.

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FLORA LICHTMAN, HOST:

If you thought red fire ants were bad - you know, the invasive, biting ant colonizing the southern U.S., costing Texas alone an estimated $1.2 billion every year - if you thought that species was worrisome, allow me to introduce you to the crazy ant. And yes, that's its real name. Writing this week in the journal "Biological Invasions," researchers report that the Tawny crazy ant can out-invade even the red imported fire ant, taking over their nests and driving them out.

In some areas where these Tawny crazy ants have moved in, they can outnumber all the other ant species there combined by a hundred to one. Joining me now to talk about the crazy ant is Ed LeBrun. He's a research associate in the Brackenridge Field Station, part of the Department of Integrative Biology at UT Austin. Welcome to the show.

EDWARD LEBRUN: Thank you, Flora. Thank you for the invitation.

LICHTMAN: Why are they called crazy ants?

LEBRUN: Crazy ants is a common name for the genus, and it stems from the way they move. All ants in this genus forage in a fairly erratic manner or what appears to be erratic manner and gives them an appearance that I guess people consider crazy.

LICHTMAN: They look like they're moving twice as fast as other ants around them.

LEBRUN: Yeah. They have a very high tempo of movement. They move very rapidly. They have long legs. They explore the environment in a lot of ways.

LICHTMAN: And what makes them so good at invading?

LEBRUN: Well, they share a suite of traits with a lot of the world's worst invasive ant species, one of which is that they are what's called super-colonial. And on a continental scale they can be called uni-colonial. What that means is that colonies don't recognize boundaries. There's no (unintelligible) population there's no aggression between crazy ants. All individuals in the population treat other individuals in the population as members of the same colony.

So you can take ants from any population in Texas, introduce them into another population in Texas or - I haven't tested this - but probably other parts of the Southeast, and they will join and work together. So that's - it really cuts down the costs of interest-specific competition and can allow the more efficient use of space in the environment they're in.

They also rely very heavily on sugary resources that they get from homoptera insects, things like aphids and mealy bugs. And they seem to be very good at exploiting these resources, which helps maintain their populations at very high densities.

LICHTMAN: I'm Flora Lichtman and this is SCIENCE FRIDAY from NPR, talking about crazy ants for the rest hour. I've been watching a lot of YouTube videos on crazy ants. And if you want to wile away the afternoon, there's no better way than...

LEBRUN: There are some good ones out there.

LICHTMAN: There are some good ones. And they seem - there are many videos of crazy ants invading electrical boxes almost to the point where it seems like there's some attraction. What is going on here?

LEBRUN: Well, it's definitely a point where people come into contact with them a lot because when your power goes out and you want to know why, you find a bunch of ants, that's a good reason to get your video camera.

Their boxes - power boxes are basically really good cavities. So these ants nest in pre-existing cavities. They don't - they do a small amount of digging but they exploit whatever cavities they can find. So that's a reason that they move into electrical boxes and pump switch - switches.

But once they get electrocuted, if you - when I've been collecting these ants in the past, you'll collect them into a vial, and they're all very agitated inside the vial. And they're - when they're agitated, they release something called an alarm pheromone, which is a signal that they used - chemical that they use to communicate with other ants if there's a threat.

If you take that vial and set it down next to a trail of crazy ants, rather than fleeing from that plume of odor, they actually turn and head towards the vial. So they seem to be attracted to their alarm pheromones - their alarm pheromone. And so as a result, that's kind of snowballs. So you're getting an ant that's electrocuted, it releases alarm pheromones, more ants to pile on.

LICHTMAN: That seems odd that they would be attracted to the alarm.

LEBRUN: There - it is a little odd, except for - a lot of ants do this. It's part of how ants organize the defensives nests, for example, so if there's an intruder you release alarm pheromones and nest mates know that there's a threat that they need to be defending against.

LICHTMAN: Hmm. Do they bite?

LEBRUN: They do but it's almost imperceptible. They're - they have pretty soft body for ants and unless they get you in a very sensitive part, you can't even feel it. But in fire ants - fire ants have a stinger so they sting. So that's what the painful part of a fire ant sting is.

LICHTMAN: What's the future of these guys? Do you think that they're going to populate the whole South? I mean is there any limit to their migration?

LEBRUN: Well, there are several limits, and we don't know what a lot of them are yet. One very important limit in the short term is that they do - they don't have winged dispersal. So they don't send out ants - winged ants to form new colonies, which means their spread is quite slow over land, about 200 meters a year radially.

So the only way that they can colonize distant places is when people pick them up and move them, which unfortunately people do a lot. And they do it because these ants like to live in these pre-existing cavities, like flower pots or plywoods you left on the ground too long or old boxes. So that's one limitation to their spread. Others are that - are abiotic(ph) limitations like freeze tolerance and drought tolerance. And we don't know yet what those are for this species.

The - my impression from what I've seen is that they are more sensitive to these things than imported fire ants are, and so that they should have a less extensive distribution when all is said and done. But those are - that's still something we've got to figure out.

LICHTMAN: Do you have recommendations for people who see them in the last 30 seconds we have?

LEBRUN: Yeah. Don't move them around. If you have them on your property or you're visiting a place that has them, take time and be careful about what you transport from there.

LICHTMAN: I think that's sounds like good advice. Ed LeBrun is a research associate at the Brackenridge Field Station, which is part of the Department of Integrative Biology at UT Austin. Thanks for joining us today.

LEBRUN: Thank you, Flora.

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