The highly invasive species of ants commonly known as ‘crazy ants’ have been spreading rapidly throughout the US southwest in recent years, generally displacing the larger and more-venomous fire ants. The reasons for this somewhat strange changing of the guard have been something of a mystery — how does the larger, more venomous species lose?

Well, according to new research from the University of Texas at Austin, the answer is clear — their offense is completely neutralized. The crazy ants produce a compound that they can secrete at will to completely neutralize fire ant venom — this is the first known case of an insect species that can detoxify the venom of another insect species.

The crazy ant invasion is just the latest wave of the ant invasions that have become common in the globalized world — the US has seen many species from the highly competitive (for ants) environments of the South American continent come and displace native species over the past 100-200 years. But at first glance it’s hard to see why the relatively small crazy ant species is so successful against a species like the fire ant. Is it simply higher population/growth numbers?

While that may be part of it, as this new research shows, there is quite a bit more to it — the crazy ants have apparently evolved specifically for combat against other ant species, and as a result have a number of significant advantages against other species.

The University of Texas at Austin provides more:

Known for their painful stings on humans and other animals, fire ants dominate most ant species by dabbing them with powerful, usually fatal venom. A topical insecticide, the venom is two to three times as toxic as DDT on a per weight basis. When a crazy ant is smeared with the venom, however, it begins an elaborate detoxification procedure, described for the first time in this study. The exposed crazy ant secretes formic acid from a specialized gland at the tip of its abdomen, transfers it to its mouth and then smears it on its body.

In lab experiments, exposed crazy ants that were allowed to detoxify themselves had a 98 percent survival rate. This chemical counter-weapon makes crazy ants nearly invincible in skirmishes with fire ants over food resources and nesting sites.





“As this plays out, unless something new and different happens, crazy ants are going to displace fire ants from much of the southeastern US and become the new ecologically dominant invasive ant species,” stated Ed LeBrun, a research associate with the Texas invasive species research program at the Brackenridge Field Laboratory in UT Austin’s College of Natural Sciences.

Commentating further on the subject, LeBrun recounts a battle that he watched between red fire ants and crazy ants near the boundary of their two populations in a field in Texas. “The fire ants found a dead cricket first and were guarding it in large numbers. Usually when fire ants amass around a food resource, other ants stay clear for fear of their deadly venom.”

“The crazy ants charged into the fire ants, spraying venom,” LeBrun continued. “When the crazy ants were dabbed with fire ant venom, they would go off and do this odd behavior where they would curl up their gaster [an ant’s modified abdomen] and touch their mouths.”

This was the eureka moment for LeBrun, when he first started suspecting that the crazy ants were somehow detoxifying. Further experiments then confirmed the theory (though in a rather cruel way I must say…).

To test the effectiveness of the formic acid, researchers sealed the glands of crazy ants with nail polish and put them in vials with red fire ants. Without the ability to apply the detoxifying compound to themselves, about half of the crazy ants dabbed with fire ant venom died. Among a control group of crazy ants with unsealed glands, on the other hand, 98% survived. Crazy ants and red fire ants are both native to northern Argentina and southern Brazil, where their ranges have overlapped for a very long time. The researchers suggest this newly discovered detoxification behavior is the result of an ancient evolutionary arms race. It’s still not clear how formic acid renders imported fire ant venom nontoxic. One possibility is that it prevents the venom from penetrating the outer layers of a crazy ant’s exoskeleton.

As the result of their impressive competitive advantages, the researchers note that likely the only things that will stop the “relentless march of the crazy ants” will be geology and climate — human intervention just isn’t that effective, on a large scale, against the species.

The new research was just published in the journal Science Express.

Image Credit: Ed LeBrun