Texas Leafcutter Ants Aided, But Also Limited, By Cold Tolerant Fungus Crops, Research Shows

Feb. 22, 2011

AUSTIN, Texas — Texas leafcutter ants farm crops of fungus that evolved cold tolerance to Texas winters, just as northern farmers cultivate cold weather crops, researchers from The University of Texas at Austin show in a new paper published in the journal PNAS Early Edition.

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Workers of the Texas leafcutter ant, Atta texana. The ants farm a fungus that is more cold tolerant than fungi in the tropical leafcutter ant fungus gardens. Photo: Alexander Mikheyev.

Though the cold tolerant fungus gives the ants the ability to maintain winter gardens, the fungus is still sensitive enough to cold, it limits the ant's ability to spread farther northward.

"The same is true for human farmers," says Ulrich Mueller, professor of biology. "Some of our crops come originally from the tropics, and humans have had to select them over time to grow in colder climates. But we are still limited by our abilities to select and adapt crops to local conditions."

Mueller and his colleagues found that even within Texas the fungus is more tolerant of cold at its northern edge near Dallas, and less tolerant of cold at its southern edge near Brownsville.

At Fort Belknap, just northwest of Dallas, Mueller says the ants "are just hanging on."

Leafcutter ants are largely tropical, and the Texas leafcutter ant, Atta texana, is one of only three leafcutter ant species found in the United States. The species arrived in the region about 10,000 years ago after the retreat of the glaciers and the end of the last Ice Age.

"The ants may have only been in Fort Belknap for a few hundreds or thousands of years," Mueller says.

The ant's symbiotic relationship with the cold tolerant fungus clearly permits it to survive in the more temperate environments of Texas.

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Ulrich Mueller inspects a Texas leafcutter ant mound at the Brackenridge Field Lab in Austin, Texas. Photo: Marsha Miller.

The finding provides a perspective on symbiotic relationships, which are normally thought of as being beneficial to both organisms.

"We normally think that forging a symbiotic relationship enriches lives — that each organism is helping the other," says Mueller. "But we have found that this can be the opposite. In the tropics, the symbiosis between the leafcutter ants and their fungal crops helped to broaden the ants' ecological niches. In the Texas leafcutter, the symbiotic relationship also constrains them."

Texas is a particularly interesting laboratory for studies of local species adaptations because of its unique ecological conditions. It is the only state in the U.S. where an unusually steep precipitation gradient from east to west crosses a steep temperature gradient from north to south, ranging from temperate to subtropical.

"Texans are uniquely positioned to monitor the effect of environmental change on U.S. biodiversity," says Mueller. "It will be interesting to see what happens with these ants over the next 10 to 20 years with global warming. Will they expand to Oklahoma and across the Mississippi River, or will cold snaps like those we just experienced knock them back?"

Mueller's research was supported by the National Science Foundation, the W.M. Wheeler Endowment and numerous Texas landowners who allowed ant collection on their properties.

For more information, contact: Lee Clippard, College of Natural Sciences, 512-232-0675; Ulrich Mueller, professor of integrative biology, 512-232-5775.

10 Comments to "Texas Leafcutter Ants Aided, But Also Limited, By Cold Tolerant Fungus Crops, Research Shows"

1.  Susan Bryant said on March 3, 2011

I believe we have leaf cutter ants on our church campus. Last year they travelled down the sidewalk, through a small yard and quite literally ate about 4 of our shrubs.
This year they are tunnelling through the grass and seem only to be eating green clover, probably because they already ate the shrubs.
My question is that this is in an area where the kids normally play volleyball or just hang out. They are fascinated by the ants, but do they bite?

2.  Deborah Jones said on March 3, 2011

How can these ants be eliminated from yards. They are destroying our plants.

3.  ellen temple said on March 3, 2011

Very interesting. Thank you.
Are Texas beloved horned toads totally dependendent on carpenter ants for food?

4.  Patrick Lutts said on March 3, 2011

Interesting article on this type of ant. We have a ranch in South Texas (Brooks County) with a real problem with leafcutter ants and our vegetation. The ants can defoliate a good size shrub overnight. We have had no luck in getting rid of them or even controlling them.
Any ideas?

5.  Craig Nazor said on March 3, 2011

I am not an ant expert, but I think horned toads survive(d) primarily on harvester ants, not leafcutter ants.

I think that one is lucky to have leafcutter ants. I had them around a house I lived in years ago, and they do benefits. One benefit is that a healthy leafcutter ant colony will keep fire ants away, which are non-native and a real nuisance (and sometimes a danger) to both humans and wildlife. I never had a problem with being bitten or stung by leafcutter ants.

Leafcutter ants are absolutely fascinating and very relaxing to watch. Unfortunately, they are rapidly disappearing out of the Austin area.

I found that they were only a problem with defoliation in the early spring - by the time late spring arrives, there is so much plant material that I didn't notice what they took. Most native plants tolerate them pretty well, and just refoliate after being stripped. With sensitive (and almost always non-native) plants that I didn't want them to bother, all I did was located their ant trail. They follow these trails through chemical signals, so I just hosed down their trails really well to the plants that I didn't want them to bother, and that usually confused them enough that they searched for other resources. Once finding another source of leaves, they left the plants I wanted to be protected alone.

They might become a problem during a drought.

These animals are real Texans, and I hope that humans can find a way to live with them. Why not plant some native plants that they like close to their colony?

6.  Mark OBrien said on March 3, 2011

Orthene gets them. Just pour it down their tunnel and so long ants. Mark OBrien

7.  Donna Payne said on March 3, 2011

We had a colony of leafcutter ants in my and my neighbor's yard in Travis Heights in Austin in the early '90s. I ended up having someone treat the queen to get rid of them because my neighbor at the time was trying to burn them out with gasoline. As soon as they were gone, I was sorry and have regretted getting rid of them since. I really missed them being around. They were fascinating to watch and really weren't that destructive. I learned that they only defoliate one species of plants at a time for more consistent farming production. I agree with Craig that we should learn to live with them.

8.  pat parker freeburg said on March 5, 2011

Our 7 year old granddaughter, Isla Freeburg Ferguson, was delighted to receive a First Prize Ribbon in the Regional Science Fair, sponsored by Austin Energy. Isla attends Bryker Woods Elementary in Austin. Her chosen subject: Leaf Cutter Ants !
pat parker freeburg: BS-1958.

9.  Pam Uszynski said on March 8, 2011

We have had some success in controlling them using wettable sulfur, found in garden centers. Mix about 1 cup with 2 gallons of water and pour down their main tunnel. This helped to force them to move out of the yard and into the pasture.

10.  Hilda Garcia said on April 9, 2012

We have a severe 'case' of cutter ant colonies at our ranch in South Texas (Duval co. south of Benavides) and have not been able to control them in spite of using a professional exterminator. The small orange grove in the property and the Oak trees really get stripped. It is sad to see the destruction and the inability to save the trees. Any suggestions on things that have worked. Thanks.