Under the cement that paves New York City lives a bustling society of tiny janitors. I’m talking about ants. There are 16.7 billion of these arthropods in Manhattan. The scavengers patrol our parks, planters, grassy medians, and cracks in the pavement, where they nosh on the food waste we leave behind, consuming intimidating quantities.
The ants work together in colonies, descending on discarded hot dogs with devastating speed, and this tiny utility they offer Manhattan is mighty when multiplied. Not even Hurricane Sandy could stop these little guys from hitting the streets and carrying off nibbles as much as 5,000 times their bodyweight.
In a recent study, scientists from North Carolina State University left out the leanest hot dogs, fattiest potato chips, and sweetest cookies all over Manhattan and watched to see who came for dinner. They found greater ant diversity than expected and hungry colonies in highway medians outeating their park neighbors. Without food-waste removal of any kind, we’d be surrounded by an amount of litter that seriously reduces well-being for humans.
I spoke with entomologists Amy Savage and Elsa Youngsteadt last week about everything from the importance of urban ecosystems to the peculiar penchant that some ants have for honeydew, a.k.a. sweet, sweet insect poop.
What inspired you to study one of the tinier creatures on Manhattan?
Amy Savage: Ants are pretty small animals, but they spend their lives in colonies, and the collective impact of a colony is significant. All over the world, ants have a strong effect on ecosystems. If you have an ecosystem-wide question, looking at ants can be a great way to get answers.
Elsa Youngsteadt: We did some back-of-the-envelope calculations on ant biomass versus rats and people in NYC and figured there are 8,000 ants per rat in the city, and 2,000 ants per human. So it’s a huge difference in terms of individuals, but rats outweigh ants 10 to 1, and humans, obviously, even more so. And yet, ants add up and make a big difference. Biologist Rob Dunn estimates that even the most rare ants in NYC, ones we know very little about, are more numerous than human New Yorkers.
How do ants spend their days in the Big Apple?
EY: One thing they do is forage for junk food! Some ants collect the sweet poop of aphids, called honeydew—a nice term for what it really is. Also, ants in North America are second only to earthworms in soil turnover.
AS: We saw quite a few ant species that are primarily carnivores living on the strips of vegetation in the middle of Broadway Avenue. They’re feeding on mostly the pests on the plantings there.
Do you think studies on urban ecosystems lag behind those of other, wilder places because we’ve been slow to realize cities are ecosystems, too?
AS: It’s not just ecologists. People in general don’t think of an ecosystem when they see a city. Some of us still don’t think ecosystems contain people, but we’re starting to appreciate how important cities are as their own ecosystems. They follow a lot of the same ecological rules of thumb. How we view them is a paradigm that’s shifting slowly.
EY: We’ve had to start thinking of how urban green spaces work as ecosystems in the way we want them to serve us.
You use the term ecosystem service a lot in the paper. What does that actually mean?
EY: An ecosystem service is anything that nature does for us for free that helps us—something we would otherwise not get or have to pay for. For example, if it rains hard, tree leaves help slow rain, soil and vegetation help soak up water, and it doesn’t flood the storm drain system.
AS: We went into urban-planning literature and found all this stuff on the effect of urban food waste in landfills and how it contributes to gases associated with climate change.
EY: If the waste doesn’t make it to landfills, it lies around as litter. Studies show people feel stressed and don’t exercise around litter. And it attracts things like rats that carry diseases.
How did Manhattan’s ants fare after the flooding from Hurricane Sandy?
EY: In this study, we didn’t look at how all arthropods were affected by flooding. We just looked at how food-removal service was affected. We can really only say that whoever is out there eating junk food came through just fine.
Why are pigeons and rats less desirable to have around the city from a public-health perspective?
EY: Rats and pigeons both harbor diseases people can get. Ants don’t. There are a few quirky cases, but in the vast majority of situations, they’re not carrying any kind of disease.
AS: The plague is an interesting one to think about because rats and fleas carried it. There were huge consequences for human health, a major loss of life, because of people not understanding that ecology. We know there’s a lot of fungi underground that will attack ants, so they splatter themselves with antimicrobial secretions. There’s an idea that it might even rub off on things they walk on.
How can urban planners use this study to better wield the power of ants?
AS: We have big urban problems, and planners try to use sophisticated designs to work around them—but it may be as simple as thinking of these insects as sharing our cities. We can help them do what they need to do—and what helps us—by making good decisions in urban planning and maintenance. For instance, maybe we shouldn’t rake the medians as frequently so they have some leaf litter. Or plant more median habitats that support diverse ant populations.
I saw in a news piece that the ants from your study are the first ones from the city to make it into the American Museum of Natural History’s collection. How did that happen?
AS: I gave a talk about how we were collecting ants all over Manhattan, and someone from the museum approached me and said she needed New York ants for the museum. I went and saw their amazing collection from all over the world, but there weren’t any from their own backyard. We, of course, are so happy to now have our ants sitting next to those of famous ant biologist William Morton Wheeler. He was a big ant guy in the early 1900s, and he wrote the book that got me excited about ants as a kid. And now my ants are next to his!
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