› Species Watch

Acid Attack

Invasive ants are harrying Hawaii’s native seabirds and causing horrifying deformities in their young.

You have no doubt read plenty of articles about how much invasive species suck. They eat crops and kill trees. They upend ecosystems, compromise biodiversity, and outcompete endangered species. Cockroaches and bedbugs even invade our homes. On the environmental beat, this is a tale as old as time.

After a while, you can almost feel blasé about invasive species. Oh, well…that’s the way life goes on this crazy planet, with all its boats, planes, and people scurrying about. Well, I’m here to get you crazy mad about crazy ants—yellow crazy ants, specifically.

Hawaii is one of the few places on earth that don’t have any native ants. Alas, just like the hog, the goat, and the dreaded Barbados gooseberry, several species of arthropod have found their way to the islands. But the yellow crazy ant may be the worst among them.

These raiders (Anoplolepis gracilipes) first said aloha to Hawaii in 1952 when they stowed away on cargo ships. Ever since, they’ve been attacking baby seabirds—with acid. It’s a heartbreaking sight.

Photo: Sheldon Plentovich/USFWS

The wedge-tailed shearwater mates and raises its young on islands in the Pacific. Adults form pair bonds that can last for years. In Hawaii, they’re known as ’ua’u kani, which means “moaning petrel” for the way the mates call out in unison.

“These seabirds can be amazingly site-faithful,” says Sheldon Plentovich, coordinator for the Pacific Islands coastal program at the U.S. Fish and Wildlife Service. “And that means they get completely harassed by yellow crazy ants.”

Now, yellow crazies are what entomologists call a “tramp ant,” which means they belong to a suite of species that are especially suited for conquest. They display excessive aggression toward other species but work cooperatively with their own, expanding territory and sucking up resources like marauding Huns while building super colonies with multiple queens.

In fact, the yellow crazy is such a nomadic terror, scientists aren’t even really sure where they originated. Some say West Africa. All we really know is that the ant empire stretches from Madagascar to the Galapagos, and it is never sated.

Yellow crazies don’t bite or sting, and they aren’t much to look at. But what they lack in size they make up for with chemical weaponry, namely formic acid. Plentovich says that when enough of them start spraying at once, the air turns acrid and will burn your nose.

What the acid does to nesting seabirds is far worse—everywhere not covered by feathers is vulnerable. That means the birds’ bills, feet, and eyes are hardest hit.

Photo: Sheldon Plentovich/USFWS

The abuse is so unbearable, adult shearwaters have been known to abandon nesting sites they’ve used for years. Remarkably, some are able to endure this torture long enough to hatch a chick. And that’s where things get really ugly.

“The chicks are adapted to stay in that burrow for safety and shelter, so they’ll sit there and just be swarmed by ants,” says Plentovich. “The parents continue to feed them, so we see chicks with big fat bellies, but as they grow, the chicks develop these horrible abnormalities.” 

Bedraggled feathers, misshapen beaks, missing toes, shrinking eyeballs…some chicks are so wounded by the ants’ acid that their nostrils grow closed and skin covers the eyelid entirely.  

Plentovich and her colleagues are hoping to publish their findings soon, but the preliminary data paints a bleak picture. At sites with a yellow crazy ant presence, nearly every chick shows signs of acid-induced abnormalities. In areas without the insects, such abnormalities don’t exist.

Clearly, a shearwater chick without eyes is doomed, and that’s depressing. But if you zoom out a bit, you’ll see how the ant’s reign affects the entire ecosystem.

John TannPhoto: John Tann

Seabirds like wedge-tailed shearwaters go out to sea to forage for fish, squid, and other seafood. And when they come back to their nests, they deposit those nutrients on land as guano—an invaluable resource for other plants and animals. So when ants drive off a colony of seabirds, it’s like they’re spraying acid on the island’s supply chain, too.

As with most invasive species, there are no easy answers when it comes yellow crazy ants (which are also wreaking havoc in Australia). On two islets, Mokuauia and Moku Nui, Plentovich oversaw the eradication of another invasive, bigheaded ants, only to see the area soon after overrun by yellow crazies.

“The best control for an invasive ant is another invasive ant,” says Plentovich. “There’s still a lot about these ants we don’t understand.”

But Plentovich and her colleagues have shown that with enough persistence, a team armed with poison-laced cat food can come close to eradicating the ants on remote islands—at least for a little while. Scientists, however, are currently unable to rid Hawaii of yellow crazies. The species is already too entrenched on the main islands, and any smaller islands nearby could be too easily recolonized by a single piece of infested driftwood.

In these circumstances, mitigation is the best we can hope for. To that end, the USFWS plans to give the ants hell at two sites (Kaneohe Bay and Mokuauia, also known as Goat Island) this March when the shearwaters return. If all goes well, they’ll be able to dial back the invasion just enough to allow the birds to mate, lay eggs, and hopefully raise a few chicks.

Who knows, maybe some of the babies will get to keep their eyes.


onEarth provides reporting and analysis about environmental science, policy, and culture. All opinions expressed are those of the authors and do not necessarily reflect the policies or positions of NRDC. Learn more or follow us on Facebook and Twitter.

Join Us