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‘Crazy ants’ use acid to survive fire ant venom

A crazy ant (left) attacks a larger fire ant (right). Scientists have just discovered that invasive crazy ants can neutralize the venom of the red imported fire ant. (Credit: Lawrence Gilbert/© Science)

Invasive “crazy ants” are rapidly displacing fire ants in areas across the southeastern US by secreting a compound that neutralizes the other’s venom.

It’s the first known example of an insect having the ability to detoxify another insect’s venom, researchers say.

The crazy ant invasion is the latest in a series from the southern hemisphere and, like its predecessors, will likely have dramatic effects on the region’s ecosystems. 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.


But when a crazy ant is smeared with the venom, it begins an elaborate detoxification procedure—it 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. The research is published in the journal Science Express.

“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,” says Ed LeBrun, a research associate with the Texas invasive species research program at the Brackenridge Field Laboratory at the University of Texas at Austin.

Researchers have previously reported that where crazy ants take hold, the numbers and types of arthropods—insects, spiders, centipedes, and crustaceans—decrease, which is likely to have a ripple effect on ecosystems by reducing food sources for birds, reptiles, and other animals. They also nest in people’s homes and damage electrical equipment.

Ants on the battlefield

In a battle for food along the boundary between the two populations at a Texas field site, 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 says. “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.”

It was then that LeBrun first suspected the ants were somehow detoxifying the fire ant venom.

To test the effectiveness of the formic acid, researchers in the lab 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, 98 percent survived.

Crazy ants and red fire ants are both native to northern Argentina and southern Brazil, where their ranges have. Researchers suggest the newly discovered detoxification behavior is the result of an ancient evolutionary arms race.

It’s unclear 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.

Apart from human intervention, the only thing stopping the relentless march of the crazy ants will be natural factors, such as arid soils or severe freezes, that will be too harsh for them to survive, researchers say. Like the fire ants before them, their range will ultimately be determined by geology and climate.

Funding was provided by the Helen C. Kleberg and Robert J. Kleberg Jr. Foundation, and the Lee and Ramona Bass Foundation.

Source: University of Texas at Austin