City ants are garbage eating, rat-fighting machines

Urban ants might be more helpful thank you’d think. According to a study published Tuesday in Global Change Biology, tiny arthropods in New York City do massive amounts of garbage clean-up — and by chowing down on your trash, they may help keep rats and other (bigger) pests at bay.

Ants are abundant in the streets of Manhattan: A recent study found 42 different species of the critters in the city. And that isn’t just a testament to Central Park’s lushness. Median strips — the tiny patches of grass between pulsing city streets — held 18 species of their own.

And as it turns out, those median-dwellers are the city’s most voracious garbage eaters. The ants that live on the medians down the Broadway corridor are capable of eating the equivalent of 60,000 hot dogs a year.

The research team tested ants’ garbage consumption by placing weighed samples of commonly dropped foods — hot dogs, cookies and chips — into wire mesh cages that only ant-sized creatures could crawl into. Next to these set-ups, they placed similar samples out in the open. After 24 hours, they took the remaining food back to the lab to measure what had been taken — by ants alone, and by the city’s entire population of refuse-eaters.

“We thought, oh, the parks, with their more diverse species — that’s where we’re going to see the ants doing a more thorough job. So we were surprised when the opposite was true,” said lead author Elsa Youngsteadt, a research associate at North Carolina State University.

Ants on tiny medians ate two to three times more than their cousins out in the park. Youngsteadt and her colleagues believe that pavement ants (so named for their habitat of choice) are probably the voracious eaters causing the imbalance.

“It really underscored for us how important it is to have different kinds and sizes of green spaces around the city,” Youngsteadt said. Parks get a lot of praise, but tiny strips of green may be where ants compete with even less popular residents.

“Outside the cages, of course, more got eaten. That tells us that other animals are competing with ants for this food. When one group gets it, the other doesn’t,” she said. And New Yorkers probably take their arthropods for granted.

When Youngsteadt was setting up her cages for the experiment, she said, a passerby asked her about her work.

“When he found out I studied ants, he said, ‘I sure hope you’re figuring out how to kill them.’ They’re definitely not popular,” Youngsteadt said. “But this study highlights that they have a purpose in the city ecosystem that we don’t even notice. They may be taking away food from rats, who it’s safe to say we like even less.”

And it seems that not even a hurricane can sweep ants away from their junk-eating posts. When Hurricane Sandy flooded many of the research sites with salty water, the team expected to see a drop-off in activity there — but local ant populations proved to be just as hungry when the waters receded.

“You’d think that several feet of salt water would deter some ants,” Youngsteadt said. She’s not sure why they didn’t drown — it’s possible they just weren’t submerged for long enough. “But it’s good news for urban ecosystems. They’re going to stick around and keep doing their thing no matter what — even when a disaster happens.”