In crazy vs. fire, the ant with the detox dance wins

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Tawny crazy ants pick fights with fire ants and win, thanks to a previously unknown way of detoxifying fire ant venom.

When dabbed with venom from fire ants, crazy ants of the species Nylanderia fulva curl their hind ends up between their legs and secrete droplets of formic acid, says ecologist Edward LeBrun of the University of Texas at Austin. The ants then give themselves vigorous rubdowns, smearing the acid on their bodies, LeBrun and his colleagues report February 13 in Science. Most survive the attack.

This detox trick could help explain why these crazy ants can vanquish the red imported fire ants Solenopsis invicta, which have been spreading across the southern United States since they invaded more than 70 years ago. They wipe out native ants, disrupt ecosystems, move into people’s yards and sting anything within reach.

In 2002, pest control operator Tom Rasberry reported an invader in Texas, what’s now called the Rasberry, or tawny, crazy ant. The “crazy” comes from their frenzied, curlicued running.

The crazy ants can take on fire ants. For the first 200 meters or so behind the front line of expanding colonies of crazy ants, fire ants are “just gone,” LeBrun says. He finds crazy ants living in what used to be fire ant nests.

Tawny crazy ants don’t sting. But in late summer and fall, they can build up in huge numbers, flooding homes with seething ant masses and ruining the insides of electrical devices. “If you’re allergic to fire ants, then it’s a vast improvement,” he says, but “for the average homeowner, probably not.”

To see how the two insects compete, LeBrun set out crickets as bait. The fire ants typically found the food first. Then crazy ants charged in, attacking with formic acid sprayed from an opening in their abdomens. Fire ants in turn exuded milky venom droplets from their rear openings.

That venom can kill many other kinds of insects, LeBrun says, but the tawny crazy ant has a combat trick of its own. He noticed crazy ants withdrawing from the fray for vigorous self-smearing and grooming.

Entomologists knew formic acid as an attack weapon. In a series of experiments, LeBrun and his colleagues discovered that it has detox powers as well. When the researchers blocked the crazy ants’ rear opening with nail polish, survivorship after venom smears decreased from 98 percent to 48 percent. The scientists then tested secretions from two glands that release compounds to that opening and found that formic acid was the critical ingredient.

Treating ants of another species with formic acid saved their lives after fire ant venom exposure.

Unlike a lot of North American ants overwhelmed by fire ants, the tawny crazy species has had time for fire ant–fighting techniques to evolve, LeBrun says. Its native range in South America overlaps with S. invicta fire ants’ original range.

The southern United States has eight or 10 species of native Nylanderia crazy ants, says John LaPolla of Towson University in Maryland. LaPolla was one of the scientists who in 2012 finally clarified which Nylanderia species had invaded Texas.

The native crazy ants, like the rest of their relatives in the umbrella group called formicine ants, should wield formic acid too, LaPolla notes. He hopes scientists will investigate whether these species also can do any battlefield detox.

DETOX DANCE  When dabbed with venom from fire ants, crazy ants of the species Nylanderia fulva curl their hind ends up between their legs and secrete droplets of formic acid. The ants then give themselves vigorous rubdowns, smearing the acid on their bodies. Most survive the attack.