REGINA BARBER: You’re listening to Short Wave from NPR. Hi Short Wavers, Regina Barber here. The city in the United States that has the most people is New York. You know the Big Apple. The place is full of skyscrapers. And if you went up one and look down, you’d see all these people, like, down below, tiny, tiny little people scurrying around from place to place, looking like ants. Real ants vastly outnumber human New Yorkers. Scientists have actually done some calculations proving this by looking at the number of ants per square foot, but most of the time, the ants go unnoticed. That’s why, as I’ve recently learned, beneath the feet of millions of people, one particular ant has managed to take over Manhattan. And I know this because of our intrepid ant correspondent, NPR’s Nell Greenfieldboyce. Hey, Nell.
NELL GREENFIELDBOYCE: Hey, Gina. I do feel like I talk to you guys about ants fairly often.
BARBER: I love it.
GREENFIELDBOYCE: Yeah. This ant has been sort of covertly conquering Manhattan since it first showed up there in 2011. And, you know, back then, researchers knew it had to be a brand new arrival because they’d been doing surveys of the city’s ants, like a few years before and, like, they hadn’t seen it.
BARBER: Wow. So 2011, that’s, like, not that long ago. Like, where did it come from?
GREENFIELDBOYCE: No one knows how it got to New York. And at first, scientists weren’t even sure what species it was. For all they knew, it might have been a species unknown to science. So, you know, you had this mysterious ant living in, like, the traffic medians on Broadway. And as you can imagine, in, like, a media capital like New York, this made headlines. Like, The New York Post dubbed it the ManhattAnt. They love their puns.
BARBER: I love it.
GREENFIELDBOYCE: But, you know, after its moment of glory, the news cycle moves on, and this ant sort of fell off everyone’s radar screens, like, for years.
BARBER: I mean, human radar screens. I wonder if, like, the other ants were aware of it.
GREENFIELDBOYCE: Oh, no doubt. No doubt. I mean, like, people who are not insect specialists generally cannot tell one dark brown ant from another. I mean, I assume the ants have no problem. But I was talking with Izzie Kaplan. She’s a student at Fordham University. That’s a couple of blocks from Central Park. And here’s what she told me.
IZZIE KAPLAN: At first, I didn’t know what it looked like, so I didn’t know what to look out for. But ever since I saw one picture, I was, like, oh my god, I’ve seen them everywhere.
GREENFIELDBOYCE: They were not hard to find. When I met her at her university’s plaza, she took me over to this concrete wall with just, like, some vines and stuff. And the ManhattAnts were crawling around. And she had this contraption with plastic tubes that researchers use to basically suck ants into this, like, little, clear vial.
BARBER: That’s so cool.
KAPLAN: I got one in here. There’s a bunch of debris in here, but you can see it climbing up the side. And it has the red thorax, so that’s how you can tell that it’s the ManhattAnt.
GREENFIELDBOYCE: It’s got this, like, reddish midsection that is so distinctive. No other ant around has that, and the ant is fairly large. So all of this means that interested people have been able to spot it fairly easily. And, you know, they’ve been uploading sightings into the iNaturalist website. And those sightings show that it is definitely spreading. Like, this is an unusual situation where you have, you know, the exact introduction time of a species known, and then, you know, it’s easy to track it because it’s distinctive and it’s spreading in a place where there’s millions of people. And what the sightings show is that this ant is not satisfied with just taking over Manhattan. It is moving into the outer boroughs and beyond. I mean, look out East Coast. This ant is coming your way.
BARBER: That’s just what we want to talk about. So today on the show, what this ant is doing, why it’s been so successful, and what happens when a new species arrives in a place it’s never been before? You’re listening to Short Wave, the science podcast from NPR. OK, now, we were talking about how scientists, like, they had really no idea what this ant was when it first turned up in New York a little over a decade ago. Like, when did they figure it out?
GREENFIELDBOYCE: OK, so the ant’s official, like, solid identification was just published this year.
BARBER: Oh, wow.
GREENFIELDBOYCE: I mean, after it was first spotted in New York, honestly, scientists kind of ignored it for a while. I mean, it wasn’t in very many places, and no one had any idea it was going to become this huge deal. I mean, one researcher told me, you know, they were busy working on other things, but this ant was busy working on New York. I was talking to Clint Penick of Auburn University, and he told me that the ant just started showing up more and more frequently when he was collecting ants in the city. And he eventually got sick of having to catalog it as just this kind of unknown species, so he and some colleagues went on a quest to, like, nail down what it was. It turns out to be an ant normally found in Europe.
CLINT PENICK: It’s quite common. So it’s found in southern England, in the Netherlands, and down in Spain, and then down to the Balkans.
GREENFIELDBOYCE: That’s why he thinks in the United States, it could eventually spread from Maine to Georgia.
BARBER: Wow.
GREENFIELDBOYCE: And when he consulted, like, the world’s expert on this species, an ant specialist in Germany, that guy was shocked to hear that this ant was living it up in the city that never sleeps.
PENICK: He was like, they’re not even really dominant in any European area. They’re not known as urban pests. And so it was quite surprising that this species, of all of the different species that could make it over from Europe, was the one that was taking over Manhattan.
BARBER: It’s so fascinating. Like, where does it live in Europe? Like, forests, small towns, or something?
GREENFIELDBOYCE: Basically forests, yeah. And I mean, occasionally in more urban areas like parks. I mean, maybe it came over to the US in the dirt around some plant roots or, you know, who knows.
BARBER: But in New York, are they sticking to parks?
GREENFIELDBOYCE: No, no. That’s just the thing. They are everywhere, the streets, the sidewalks, the trees. One researcher told me, there’s ants on her stoop. She passes several colonies as she walks through Trader Joe’s. I mean, it is all over Manhattan, and it has moved north up into the Bronx, south into Long Island. Clint Penick told me one day he went to a friend’s place over in New Jersey, and when he got off the subway–
PENICK: ManhattAnts were there. So, like, at this point, they had crossed the Hudson.
GREENFIELDBOYCE: These ants are probably spreading during their mating season. That’s when they sprout wings and can fly short distances. And, you know, so far, they’ve been moving out about like a mile a year, although at some point, they could hitch a ride and spread farther. And, you know, they could already be in more far flung places and people just haven’t noticed.
BARBER: Yeah, because what we said, like, people don’t often notice, like, ants.
GREENFIELDBOYCE: Yeah, unless they bite or sting, which these don’t. Actually, though, to be fair, these ants do sometimes get noticed. Like when they climb way up into Manhattan high rises, that is actually unusual for an ant to do. And so, like, The New York Times did a story a couple of years ago about why people were suddenly seeing ants, like, up on the 20th floor and stuff like that. Besides being climbers, these ants are also unusual in that they are speed walkers. They move really fast.
BARBER: I mean, I’m still getting over them, like climbing 20 floors. But OK, so they’re moving really fast, like other New Yorkers? Like, I’ve only seen this in movies.
GREENFIELDBOYCE: Yeah. You see people famously kind of rushing through the streets. Clint Penick told me ants normally avoid the sidewalk, except, you know, there’s this urban ant called the so-called pavement ant. It’s this other introduced species from Europe that’s now in a lot of US cities, including New York, but it’s clear in New York, the pavement ant now has serious competition.
PENICK: I started to see these huge foraging trails with hundreds, if not thousands, of these ManhattAnt workers just running along the sidewalk. And so this is, you know, the first time we’ve really seen an ant take over the sidewalk in New York City since the arrival of the pavement ant, which was, you know, at least 150 years ago.
BARBER: Wow.
GREENFIELDBOYCE: The pavement ant has long been the most common ant in New York, but now, the ManhattAnt is vying for that title.
BARBER: OK, so these ManhattAnts are, like, everywhere. Should this worry us? I mean, is this ant doing anything that’s, like, bad for people or other living things?
GREENFIELDBOYCE: That is what is so interesting to me. No one knows if it’s going to be trouble here. I mean, ecologists talk about something called the 10% rule, and that basically says most non-native species that are brought to a new place, like in a ship or something, they don’t survive there. Only about 10% get established and settle in. And of that minority that manages to persist in a new place, most species don’t disrupt things. Only about 10% of new settlers will become invasive pests. So, you know, is this ant going to be one of that small minority that gets to be considered damaging and invasive? I mean, we don’t know. It’s not clear.
BARBER: Wow. OK. Well, what do we know about how those ants live? Like, how are they making their living?
GREENFIELDBOYCE: So I talked to Samantha Kennett. She’s currently a PhD student at Clemson University. She’s done a lot of work in New York on this ant. She says, unlike the pavement ant, this one doesn’t really focus on human food, although, you know, in a pinch, these ants will consume some human food to some degree.
BARBER: Interesting.
GREENFIELDBOYCE: But their main sustenance is honeydew. So that’s a kind of sugary poop that’s excreted by aphids and other pests, like scale insects.
BARBER: Wow. You got me at poop. I’ve literally never heard, like, aphid excrement be called honeydew. I love it.
GREENFIELDBOYCE: It’s a nice name for what it is. And the ants are going up into, like, street trees to get this stuff.
SAMANTHA KENNETT: That’s part of how they’re so successful, is they’ve been able to– they’re foraging in street trees for honeydew.
GREENFIELDBOYCE: But listen, scientists know that ants that like honeydew can sometimes turn into, kind of, like, honeydew farmers, right? Like, they want to get this stuff. And so they start to kind of, like, take care of the insects that make it, right? They kind of herd aphids. They protect aphids from other predators. And that means you end up with more aphids and other similar plant pests chewing on the plants of New York.
BARBER: So that doesn’t sound great for these city trees, right?
GREENFIELDBOYCE: I asked Samantha Kennett about that, and she says it’s entirely possible that, you know, this ant could be changing something for city trees, but we don’t know.
KENNETT: I think it would be really interesting to see how in the long term, the ManhattAnt could have effect on trees in New York or anywhere that they are invading.
GREENFIELDBOYCE: It’s also not clear how this ant is going to interact with native ants. Ants can battle with each other, and scientists know that invaders can sometimes wipe out native ants. That’s a big deal because native ants can play important roles that affect other species. They do stuff like disperse plant seeds in forests. I mean, ants are small, but they are numerous. And that means their activities can have major consequences, sometimes weird, unexpected consequences. I mean, earlier this year, for example, scientists published one study showing that, when an invasive ant came to Kenya, it wiped out a native ant. And this led to a series of ecological changes that ultimately resulted in lions eating fewer zebras.
BARBER: That’s really fascinating. And it seems really strange that this ant that’s, like, spreading all over New York and further out, like, no one knows what effect it will have.
GREENFIELDBOYCE: I know, right? I was talking to Ellen van Wilgenburg. She’s a researcher at Fordham University who’s gotten interested in this ant, and she also studies the spotted lanternfly. You know that one? You know that plant pest, you know, is from Asia. And when it turned up on the East Coast, there were all kinds of news, articles, and TV, and everybody was urged to destroy it. You know, there was, like, a huge amount of media attention.
BARBER: Oh.
ELLEN VAN WILGENBURG: Then something like the ManhattAnt is there. It’s probably more abundant even than the lanternfly, and no one knows.
GREENFIELDBOYCE: She says, if you look at an influential list of the top 100 most destructive, invasive species in the world, there’s, like, five different species of ants on there. So it’s like researchers right now are in this weird kind of limbo. All they can do is watch the ManhattAnt go and try to understand what’s happening. That’s one reason why on this website, I mentioned earlier, iNaturalist, they set up a Project ManhattAnt page, where people can upload sightings and observations. Although you know, the ants are so speedy, it can be hard to take a picture, but people do it.
BARBER: I think Short Wavers are up to this challenge. I mean, I am.
GREENFIELDBOYCE: I mean, I know definitely the next time I go to New York, I’m going to be looking for it.
BARBER: It’s like real life, like, Pokemon Go. Nell, thank you so much for bringing this story to us.
GREENFIELDBOYCE: As you know, I am always one for ant news, and I will bring you everything I find.
BARBER: Looking forward to it. This episode was produced by Rachel Carlson. It was edited by our showrunner Rebecca Ramirez, and Nell checked the facts. Ko Takasugi-Czernowin was the audio engineer. Beth Donovan is our senior director and Collin Campbell is our senior vice president of podcasting strategy. I’m Regina Barber. Thank you for listening to Short Wave from NPR.
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