How Ants Make Our Cities Healthier
JESSICA WARE (Curator, Division of Invertebrate Zoology): Cities are one of the only habitats in the world that are growing in size, but we’re just starting to understand how they work as ecosystems. When you think about wildlife in the city, it might not be exactly alluring… But if you start looking on a smaller scale, you realize there are diverse insect societies whose tiny cities mirror the busy human streets surrounding them: ants!
These are Tetramorium immigrans—pavement ants. They live in cities all over the world, and they like the same kind of food we do. In fact, they love it when we humans drop our crumbs.
Researchers calculated that the ants (and other arthropods) living in just these street medians on Broadway could eat close to a ton of food waste every year—equivalent to 60,000 hot dogs or 600,000 potato chips.
And these tiny little ants could be helping us out in big ways—maybe even making our cities healthier places for humans…
[INSECTARIUM title animation]
DIRECTOR [off-camera]: Hypothetical: you are hit by an incredible shrinking ray.
[On-screen text: Jessica Ware, Ph.D. | Curator, American Museum of Natural History]
WARE: As it happens. It happens to people.
DIRECTOR [off-camera]: It does. You’re shrunk down to the size of an ant in New York City. What are the challenges that you are facing, or that an ant might face?
WARE: Well, I mean, the city- a city like New York City, in theory it’s designed to help humans move places very fast. Right?
[On-screen text: Susan and Peter J. Solomon Family Insectarium | American Museum of Natural History]
WARE: And when you’re moving very fast, you’re often not looking at the ground to see little ants that are scurrying around. So, you run the risk of being stepped on, bicycled over, driven over. There’s of course insecticides that people spray. And the temperature. Sometimes it’s a little bit hotter in cities than maybe what you might be adapted for.
Because in cities, you have a lot of buildings and pavement that trap heat, creating these urban heat islands that can be many degrees hotter than nearby areas.
It would be tough to be a city ant.
DIRECTOR [off-camera]: But if you can make it here, you can make it anywhere.
WARE: You know, I’ve heard that’s true. That’s true.
DIRECTOR [off-camera]: Well, ants have definitely made it to my kitchen. Where else are they hanging out?
WARE: Ants are pretty much everywhere. So, the rainforest, temperate forest, the beach, the desert. Pretty much anywhere on Earth, there are ants. In terms of sheer numbers, there’s more ants on the planet than there is almost anything else. So, for every human on earth, there’s 2.5 million ants. That’s a lot of ants.
If you think about it, we’re really living in their cities. And that’s because ants play an outsized role wherever they are, whether it’s in a city or a rainforest. Take these leafcutters… They—not mammals or birds—consume the most vegetation in Central and South America.
They don't eat these leaves. They don’t eat this as food. This is actually food for the fungus that they're growing. And then they eat the fungus. They're basically farmers. And leafcutter ants are just one kind of ant. There’s 14,000 species of ants. They're all in this one family, Formicidae.
[On-screen text: Formicidae | ants]
WARE: And we think there are lots more species out there, just waiting for scientists to give them names.
DIRECTOR [off-camera]: Very cool. So why are there so many different kinds of ants?
WARE: Well, I mean, that's always a good question. One thing for sure that we know is that ants, individual ants, are actually quite small. And perhaps them being this kind of fun size, tiny insect size that allows them to occupy lots of different niches in one area.
That means opportunities arise for all kinds of specialists and all kinds of ecological roles.
[On-screen text: Broadway and 73rd Street | New York, New York]
WARE: Oh look look look look. There’s an ant coming! There’s the crumb. You did it!
Remember those ants that eat 60,000 hotdogs a year? Dr. Amy Savage was one of the scientists who calculated that number.
[On-screen text: Amy Savage, Ph.D. | Assistant Professor, Rutgers University]
WARE: She’s also done research to understand just who our ant neighbors are.
AMY SAVAGE, PH.D. (Assistant Professor, Rutgers University): I had done this research for my Ph.D. in Samoa, out in the middle of the South Pacific. And I thought, why- why am I trying to do this thing where I go far away? And so then, when I did the next research project, I said, “What’s happening under people’s feet?” I realized that people were a part of the story I was trying to understand about insects. So, I went to the most urban place in America and started looking on Broadway, the ants on Broadway.
WARE: I’ve always been told you should dig around where pigeons have just been. What could happen, right?
The city isn’t just one big slab of concrete. Just like there are different neighborhoods, there are different microhabitats—like these street medians.
SAVAGE: I got to go into these islands of green, in the middle of a street that’s just surrounded by inhospitable landscape, like pavement and buildings. I started to do some research trying to understand just the diversity in these systems.
We collected all along Broadway and we even collected down in lower Manhattan. What we were expecting to find was three exotic ants and maybe an occasional native one. And what we found were 24 species of ants in the street medians of Broadway. It was way more diverse than we thought it would be. And it’s really exciting to see what they’re doing.
[On-screen text: Entomology Department | American Museum of Natural History]
WARE: Amy actually donated many of the ants she collected to become part of the permanent research collection at the Museum.
SAVAGE: These are really special to me. These were collected right here in New York.
WARE: So, Amy, what kind of ants live in New York City?
SAVAGE: Most of them are native ants, in terms of diversity. In terms of the sheer numbers. we got a lot of pavement ants in cities.
WARE: Pavement ants are originally from Europe, but populations have changed so much as they spread all over the world that they are now a new species. They were almost so common that no one bothered paying attention to them in a scientific sense.
SAVAGE: For the longest time they were known as Tetramorium species E. They didn't have a name.
[On-screen text: Tetramorium species E]
WARE: But starting in 2017, researchers started gathering the data they needed to redefine the species as Tetramorium immigrans.
[On-screen text “Tetramorium species E | pavement ant” flips to “Tetramorium immigrans | pavement ant”]
One of the native species Amy collected was Prenolepis imparis, the winter ant, which is usually more active in colder weather.
[On-screen text: Prenolepis imparis | winter ant]
SAVAGE: During the summer they estivate, which is kind of like hibernating. They go to sleep when it’s really hot out. It was one of those species that we were really thinking would struggle in cities. And instead, even in August on hot days, we’re seeing Prenolepis running around in New York City. So, there’s something really interesting happening with them.
WARE: There are lots of scientific mysteries to uncover in the patchwork greenspace of pocket parks, cemeteries, soccer fields, medians, and street tree beds scattered throughout our cities. But we already know these spots are vital for both people and ants.
SAVAGE: They end up being really important for the people who live in cities, both psychologically and physiologically. And they’re also important for maintaining this diversity of species that provide ecosystem services.
WARE: And one ecosystem service that city ants perform is helping to clean up our food waste. It’s almost a cliche that ants will invade a picnic—but it may be surprising just how important their sanitation work can be.
SAVAGE: I think people have a good sense that if there’s just food lying on the ground, it’s not a good thing. But even if people are good and put their food in a trash bin, it still goes to a landfill.
WARE: One study found that Americans in three cities—NYC, Denver, and Nashville—throw out an average of 3.5 pounds of food waste per week. A lot of that ends up in landfills where, as it rots, it emits methane—a significant contributor to the rise in greenhouse gasses.
SAVAGE: So anything that an urban animal like an ant can do to just process that food at the source is going to be an ecosystem service for everyone because of climate change.
WARE: A bonus is that unlike other city food scavengers, ants aren’t nearly as likely to spread disease to us humans than animals like rats, racoons, or birds.
As the paper Amy co-authored puts it, ants’ contribution to urban waste removal is “modest but notable.” So, of course, ants alone aren’t going to solve global climate change—that’s still on us humans—but we should give them credit for the role they play in greening our cities. And while ants are changing our cities, we’re also changing their tiny worlds. It’s a symbiotic relationship where we’re adapting to one another as we learn how to live together.
SAVAGE: We don’t drop our hot dogs, we drop our buns. And so, there’s a lot of carbs. And we know that ants don’t have a long evolutionary history eating these weird foods that we drop. Our food is actually changing their behaviors.
WARE: With a carb-heavy diet, rather than one full of protein, like they may have in more rural spots, Amy observed that ant colonies enter survival mode: they tighten up their colony size because they’re not able to support large numbers of workers. And Amy’s research has shown that city ants are becoming more voracious predators: pouncing when they come across scarce insect prey and preferring crickets over corn chips.
SAVAGE:One really cool thing about studying ecology and cities is that cities provide us a glimpse of one possible global future. We are an urban species now. It’s really fascinating to think about what does the future world look like. I like going places like Singapore where there’s plants growing down the sides of buildings that help cooling down without air conditioning units. There’s walls of just vegetation that have a bunch of species flying all around them.
WARE: We often think of urbanization as kind of like a bad word, right? But what you’re saying is that urbanization can be done in a thoughtful way that could preserve some of the species diversity and the human health aspects that we like about rural settings?
SAVAGE: It could and, you know, I always have this vision of people walking through a city the way that they walk through a forest in a hike. How can we look to nature to make our cities more of a place that we want to be?
WARE: While we still have a lot to learn about urban ecosystems, if we’re aware of the small players all around us, we’re more tuned in to the idea of a city as our habitat and what we and our tiny neighbors need to thrive.
[Credits roll]
WARE: You might have seen some cool pavement ant behavior without even realizing it.
Maybe you overlook them when it's a single individual walking around. But you may have seen pavement battles where there's large groups of pavement ants that will kind of line up facing each other with a little bit of a gap between them. Well, it's not so much like a battle as it is almost like a dance-off. You know, if you've seen West Side Story—very West Side Story.
Like their name suggests, pavement ants like to live under slabs of concrete and they’re very territorial. Their battles usually happen in the spring and early summer when they’re trying to establish their territory.
These are turf wars where the conflicts can go on for hours or even days! While there’s plenty of pulling and wrestling—and some ants are definitely killed—fatalities are comparatively low. So, keep an eye on the sidewalks the next time you’re walking around the city and appreciate the world of tiny wildlife!
In pavement cracks, roadside medians, and parking lots, there are incredible miniature civilizations booming within our concrete jungles: ants! We don’t often think of urban areas as having “ecologies” but Amy Savage, Ph.D. studies the amazing diversity of ants making their way in the city. Their combined efforts make our urban landscapes greener places to live, but their newfound love of carbs is also changing things for them...
Our host and museum curator, Jessica Ware, Ph.D. joins Amy in a search for some tiny neighbors. They're managing surprisingly well in New York and other cities by adapting to human food. But without the access to easy protein (e.g., other insects to prey on), they're doing things a bit differently in street medians than they would in a more rural setting.