The Enemy Is Armed With Acid. We’re Armed With Cat Food, Corn Syrup, and Neurotoxin.

Slate’s animal blog.
Dec. 6 2013 4:37 PM

Invasion of the Crazies

Yellow crazy ant, Anoplolepis gracilipes, is an invasive and destructive pest across the tropics. Poon Saan, Christmas Island, Australia, April 2011.
Yellow crazy ant, Anoplolepis gracilipes, is an invasive and destructive pest across the tropics. Seen here on Christmas Island, Australia.

Photo courtesy John Tann/Flickr

Three days west of Hawaii by ship, there lies a desolate strip of nothing named Johnston Atoll. Over the last century, the island has played host to a military base, thermonuclear warhead tests, and landfills containing everything from asbestos and Agent Orange to plutonium and sarin nerve gas. But of all the nastiness inhabiting Johnston Atoll, nothing is more dangerous to native wildlife than the yellow crazy ant.

At first glance, yellow crazy ants (Anoplolepis gracilipes) are underwhelming. They neither possess massive pincers nor inflict debilitating stings. But as their name suggests, these little beasts have a dark side. The crazies are known as “tramp ants” because they can cross the high seas by driftwood or by stowing away in the holds of ships—and once they hit the beach they’re able to colonize nearly any patch of earth they land upon. Worse, these pirates are voracious. They build massive, cooperative nests and then erupt out of them when the sun starts to set, consuming anything in their path. Sometimes that means eating the tiny drops of honeydew excreted by sap-sucking insects. In other cases, as in this video of the Johnston Atoll National Wildlife Refuge, it means storming over colonies of ground-nesting seabirds.

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As you can see, yellow crazy ants do not make nice neighbors. The little beasts cannot bite or sting, but they do have another weapon: They subdue their prey by spraying acid.

It’s so bad, says Sheldon Plentovich of the U.S. Fish and Wildlife Service, that when she’s close to one of the ant nests, the formic acid gets so thick in the air it makes her eyes sting. And it tastes like burning.

“The thing that makes them especially harmful is that they’re capable of reaching really dense numbers. On Johnson Atoll, you could stand there when we first discovered the infestation and your feet would be covered in ants,” she says. “It would make most people want to keel over and die.”

Of course, Plentovich is not most people. She and her Crazy Ant Strike Team—yes, that’s the official name—have been working to eradicate the crazies on Johnston since the invasion was first noted in 2010. She’s also a champion kiteboarder and surfer, and while she doesn’t mind getting ants in her pants, she does take precautions against plutonium contamination when digging up a nest. “I’m super sensitive to that,” she says. “You know, because I had leukemia a couple times.”

Michael Jordan who? I want a poster of Sheldon Plentovich and the Crazy Ant Strike Team for my office wall. (Make this happen, USFWS.)

In addition to hunting down invasive ants, Plentovich has been trying to understand how badly formic acid affects native wildlife—and the preliminary research is not good. The acid appears to interfere with the keratinization (or hardening) of chicks’ bills. In adults, the acid makes birds’ eyes swell shut and causes temporary blindness. I say temporary because it’s possible (though unlikely) that the blind birds that escape Johnston might recover while they’re out at sea. The researchers have no way of knowing, though, because none of the birds they’ve tagged who were exposed to acid have ever come back.

One beetle was no match for a host of Yellow crazy ants, Anoplolepis gracilipes. Poon Saan, Christmas Island, Australia, April 2011.
One beetle is no match for a host of yellow crazy ants.

Photo courtesy John Tann/Flickr

Obviously, this is bad news for struggling bird populations. This tiny, humble strip of sand is actually one of the only suitable nesting sites for seabirds for about 750,000 square miles. (Invasive rats rule the roost on many other Pacific Islands.) When Plentovich and company first arrived on the atoll, the birds had abandoned every patch of earth near the ant invasion. Terns had no problem nesting on the nearby asbestos dump, but yellow crazy ant territory might as well have been scorched earth.

But that was before the USFWS brought out the big guns—by which I mean squirt guns full of cat food, corn syrup, and neurotoxin. Just like the ant traps you use in the kitchen, the sugary syrup attracts the workers to the poison and convinces them to take it back to the nest. Queens crave protein, so the workers make sure some of the cat food bathed in neurotoxin makes it up the social ladder.

This is an absolutely crucial component to ant eradication. In their native habitats, yellow crazy ants produce nests with around 300 queens. Pretty impressive, right? Well, on Johnston, without any of the ants’ natural predators, the crazies boast supernests of 800 to 1,000 queens, and because they’re all sisters, there’s no aggression or competition between the armies. If you fail to kill just one queen, the infestation reboots.

The Crazy Ant Strike Team has endured blistering heat, long hours, and weeks of inglorious sea travel to get the yellow crazy ant population to just 5 percent of what it was three years ago. The last remaining nests may prove the most difficult to snuff out simply because the island is no longer swarming with crazies.

“If they glowed in the dark, it’d be a lot easier,” said Lee Ann Woodward, the USFWS’s resource contaminants specialist on the project. Woodward was the one who initially spotted the ants in 2010 while checking up on the island’s numerous landfills of scary stuff. She joked, “I almost wish they would pick up the plutonium so we could detect them somehow.”

In the meantime, birds are again nesting in their former territory, and other ants (also invasive, though not nearly as big of jerks as the crazies) now occupy the newly vacated territories. Though the job isn’t quite finished, it seems important to take a moment to enjoy this small, uncommon victory in the battle against invasive species. Just across the sea in Hawaii, yellow crazy ants have marauded across the mainland from shore to mountaintop—an infestation likely past the point of no return.

Of course, Plentovich isn’t claiming victory over Johnston Atoll just yet. “It depends on how you measure success,” she says. “For me, I want them eradicated. And we’re not there yet.”

After all, if there’s just one queen laying low beneath the asbestos, Johnston’s ant army will rise again, and the island’s seabirds will suffer. Well, the seabirds and the humans brazen enough to try to save them.

Jason Bittel serves up science for picky eaters on his website, BittelMeThis.com. He lives in Pittsburgh. Follow him on Twitter.