The Rise of the Crazy Ants

Ants equipped with venom antidote invade southeastern U.S.

The English had the longbow. The Spanish had steel. Tawny crazy ants have their own formidable weapon—a protective acid sheath—that protects them against fire ant enemies. The revelation comes from a new study published this week.

Named for their butterscotch color and erratic movements, tawny crazy ants are the newest insect invaders sprawling throughout Texas and the Gulf states, unseating the reigning imported fire ants that have infested the region. Teeming out of electrical outlets and short-circuiting electronics, the tiny reddish-brown crazy ants have been making headlines as their numbers climb in the southeastern U.S. In some locales they can be so tightly packed together they are initially mistaken for dirt. Then they move.

As their population swells, the ants, formally known as Nylanderia fulva (but also sometimes called Rasberry crazy ants in honor of the Texas exterminator that discovered them), are harming the environment—not to mention people’s homes and electronics. Now we have a new clue as to why they are able to prevail over the previously dominant fire ants: Crazy ants produce chemicals they then rub on themselves as an antidote to fire ant venom. And the acidic substance exuded from where a stinger would be located on other ant species also doubles as a chemical weapon they spray at foes, allowing the crazy ants to defeat competitors that would otherwise help keep them in check.

The discovery stemmed from some initial observations of odd, and sometimes disturbing, ant behavior. Since these ants, native to northern Argentina and southern Brazil, first started showing up in Texas in 2002 it has been unclear why they were able to flourish. But it is undeniable that they do. When fire ants and crazy ants show up in roughly equal numbers and go for the same tasty cricket treat, new work reveals that the crazy ants typically win some 93 percent of the time. Moreover, many crazy ant colonies have been spotted inside fire ant mounds that still are home to some of their previous tenants, raising the alarm among bug experts that crazy ants can apparently snatch active nests from their cousins with ease.

Edward LeBrun, a researcher at the University of Texas at Austin, and his team published these and other findings February 13 in Science. One of the team’s astute observations that fueled their research into the ants’ chemical arsenal: crazy ants that had been involved in fire ant skirmishes typically engage in a very particular behavior sequence. After a run-in with a fire ant a crazy ant would stand on its hind and middle legs, fully curl up its body to touch its glandular opening at the tip of its abdomen to its mandibles, and then seemingly groom itself vigorously, rubbing a secretion along itself to apparently detoxify the venom. LeBrun’s team decided to dive further into what was happening.

That’s where the nail polish came in.

For this work LeBrun placed a dab of nail polish on the insect’s glandular hind opening to block it from exuding its secretions, and then, to create a control group, put an equal amount of nail polish on the sides of other crazy ants. Then he placed the ants among attacking fire ants. Crazy ants without blocked glands were able to hold their own—surviving attacks by the fire ants almost 100 percent of the time. Among the attacked crazy ants with blocked capabilities, about half died. And although some of the ants with sealed openings may have survived because the nail polish bubbled and allowed tiny bits of the protective secretions to emerge, the still-striking differences in survival rates indicates that this secretion and accompanying movement was protecting the ants.

The glandular secretion previously identified as formic acid was already known to be sprayed by the crazy ants as part of a defense mechanism, but this is the first work that has found an ant species apparently detoxifying itself with the substance. The researchers also tested the acid’s protection capabilities by exposing yet another ant species to either the fire ant venom and the possible crazy ant antidote or just the venom with a placebo. Only one-fifth of the ants without the antidote managed to survive compared with 100 percent of those that received the crazy ants’ formic acid. That’s a striking difference. Exactly how the formic acid works as a defense mechanism—whether it denatures the enzymes from the fire ants’ sting or changes the biological activity of the venom—remains unknown, Lebrun says. But the protective numbers do not lie, shedding light on a biological process at work.

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The finding comes at a time when the ants are spreading and displacing fire ants from the southeastern U.S. Their growth is bad news for the ecosystem because it is reducing the numbers of other arthropods like spiders and centipedes, which are staples for birds that would normally sup on them but would not typically eat the less tasty crazy ants. “It basically means that there will be a reduction in the amount of the food at the base of the food web which will ripple up to creatures like birds,” LeBrun says.

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