Can New York City Win Its War on Rats?

Sometimes, we go to war with our neighbors. And sometimes those neighbors are rats.

Robert CORRIGAN: Okay, so we’re outside in New York City, looking at what we call active rodent signs, or A.R.S.

That is Bobby Corrigan. He is an urban rodentologist — a former rodent researcher who now works for the City of New York.

CORRIGAN: Everyone thinks there’s a rat world below our feet and to some degree, that’s true. But rats have a very specific subterranean environment they need. 

It is a cold and windy afternoon in Lower Manhattan, one of the oldest parts of the city. Most of the humans have scurried back to their offices from lunch. At the intersection of Murray and Church Streets, Corrigan points to a sidewalk curb that has collapsed in on itself.

CORRIGAN: And that’s because the rats nearby got below the sidewalk, tunneled into this area, dug out the soil so they can have a burrow in this area, and now there’s nothing supporting these heavy concrete pieces. It’s expensive to put in a new curb.

And where did these burrowing rats come from?

CORRIGAN: Just five feet away, we have the proverbial catch basin that the storm water drains down, and sometimes you’ll see rats come right out of these sewers. Their home is in the sewer in the middle of the street. 

So you’ve got rats in the sewers, rats burrowing under the sidewalks. What else can we see?

CORRIGAN: I want to show you something much more interesting. You’ll notice along this building perimeter, if you let your eyes just continue along, you will see the gray concrete that’s light. But next to the building, you’ll see this dark charcoal stain that’s linear. The stain goes around, hugs the building. That is from rats. That’s what’s called a sebum stain. Rodents like to hug walls, so they feel safe and secure. So that’s a very clear sign. And if you came here between 10 and 2 tonight, chances are good you might see a rat running along there. 

Bobby Corrigan, as you can tell, is something of an enthusiast when it comes to rats — although his enthusiasm is a strange blend, of appreciator and exterminator.

CORRIGAN: I want to be humane to this animal because I respect it. But if you put a rat on my airplane when I’m flying over the seas to Paris, I want that rat dead in any way possible! 

He acknowledges that his work has its disadvantages.

CORRIGAN: My wife, when we go out to eat, before we step into a new restaurant, she’ll say, “Is it safe?” There’s days I wish I didn’t know what I know.

When you walk around these old city streets with Corrigan, it’s easy to feel that it’s a rat’s world and we’re just living in it. As we learned last week, in part one of this series, New York and other cities are struggling to control their rat populations. The problem here got so bad that the city declared war on rats. Today on Freakonomics Radio, how do you execute such a war? This one began with a summit:

Mayor Eric ADAMS: Wow, I didn’t realize we’d get so many people showing up to talk about rats.

We’ll hear about some battle tactics:

Kathleen CORRADI: An ounce of prevention is worth a pound of cure. 

But what if it’s too late for prevention? 

Jessica TISCH: New York City is not going to be the first city to do this. In fact, we are definitely going to be one of the last.

We’ll hear about rat traps, rat poisons, rat birth control.

CORRIGAN: You know, birth control on paper sounds pretty darn smart, right? 

And we’ll consider some other ideas.

Ed GLAESER: If prepared well — sure, I’m open. Is someone actually serving Norway rat?

You want fries with that rat? Part two of “Sympathy for the Rat” begins now.

* * *

Bobby Corrigan was born in Brooklyn, but his family moved out to the suburbs of Long Island when he was a kid. This suited Bobby well.

CORRIGAN: I guess I’ve always been a nature nerd. I was the kid that was in the backyard, frying the ants with the magnifying glass, while my brother played football. And so I’ve always followed that path, of creepy crawlers and animals that were mysterious but cool, and things we didn’t know much about. 

Still, he didn’t plan on a life devoted to extermination.

CORRIGAN: You know, it’s kind of crazy. I came from a poor family. I had no money to go to college, so I answered a newspaper for an exterminator in New York City. And the new guy gets the good job, right? So they put me in the sewers to hang rat poison. I was frightened to death, to be honest with you.

But that fear only boosted his interest. After working as an exterminator for a few years, Corrigan did go to college, and he studied under a prominent entomologist named Austin Fishman — a “pest-control pioneer,” Corrigan calls him. After that, Corrigan joined a graduate program at Purdue University, in their School of Agriculture.

CORRIGAN: So when I got into grad school, and I signed on to studying rats as my species, I moved into barns that were full of rats. This was in Indiana, and farmers would tell me, “We’re always fighting rats.” So I asked if I could just move into their barn. I would camp literally on the floor inside these rat-infested barns. And over time, it’s a whole crazy experience that you get to realize just how amazing these mammals are. I have to say, looking back, it was some of the most exciting years of my life. I say that with all seriousness.

Corrigan wound up getting a Ph.D. from Purdue, in rodent pest management. And he stayed out there for a while, as a professor. But eventually he felt the siren call of his hometown, and he took a job with the New York City Department of Health and Mental Hygiene. In a way, this was a very rat-like behavior, as rats experience that same pull toward home.

CORRIGAN: I use the term “long rodent.” We all know what long Covid means. Well, long rodent is — you know, once the colonies have become comfortable and had many, many families, they’re laying down all kinds of pheromones with their bodies. They’ll call any new rats into that area. They also have memories of their own neighborhoods, just like we do. So those neighborhoods, once they become really infested — there’s a reason for that, the rats have found this works for us, and that’s going to continue and be passed on to generation after generation. 

From the rat perspective, that sounds lovely — “from generation to generation,” the kind of thing that humans cherish. But from the human perspective, rats are rarely a thing to cherish. Most people see them as disgusting pests, at the very least; some people think of them as mass murderers — although as we heard in part one of this series, some scientists have recently exonerated rats on the charge of having spread the Black Death in Europe. Still, the rat’s reputation is terrible. So if you are facing the kind of multi-generational infestation that Bobby Corrigan was just talking about, what do you do? The most obvious tool, in many cases, is poison.

CORRIGAN: Poisons — they’re called rodenticides, meaning to kill rodents — are a primary tool that everybody uses to try to kill any rats that they see around their property.

But Corrigan says this obvious choice is often the wrong choice.

CORRIGAN: You would want to start first with not attracting the rats with food or clutter in the first place. Poisons are probably the last resort that should be approached when it comes to rat control. It’s an environmental thing. 

A good example of the environmental threat of rat poison is the story of Flaco the owl — a beautiful Eurasian Eagle-Owl who lived in Central Park Zoo in New York City. Flaco became a celebrity when, in 2023, he escaped from the zoo — thanks to a vandal cutting a hole in the cage — and he took up residence in Manhattan. There were concerns at first that he wouldn’t be able to survive outside of captivity. But he seemed to be thriving.

CORRIGAN: When I read that, I said, well, I am worried about this owl because I know the owls of the parks, they are preying upon rats and mice out in the parks, and may be feeding on these poisons. 

After nine months on the outside, Flaco was killed when he flew into a building on the Upper West Side. A postmortem showed he had debilitating levels of rat poison in his system. But it’s not just escaped zoo animals who are endangered by rat poison: dogs are, children are. Like Bobby Corrigan said, poison should probably be a last resort, not a first. And how does Corrigan feel about rat traps?

CORRIGAN: Traps, if they’re applied by someone who’s experienced, and it really does take experience — the rat’s a very wily mammal and it’s very smart, it’s not as simple as going to the hardware store, buying a rat trap, putting it out with a glob of peanut butter and saying, that’s it — so traps can be useful when done by experienced people. But we have to acknowledge that many of them are simply inhumane. Especially glue traps — you know, if you ever sit and watch a rat or a mouse struggling on glue, it’s not a pretty sight whatsoever. 

We talked in part one of this series about the thin line between animals we love, and treat kindly, and the animals we consider pests, and treat violently. It is true that some people do keep rats as pets; and of course we’ve used them for years as research subjects in medicine, psychology, even space travel. But we mostly think of them as a thing to be eliminated. Even though they are, like us, mammals, and not so different from the mammals we celebrate, and love. So does it make sense to torture a rat when you wouldn’t torture a cat or a dog? Another rat-mitigation solution that’s been gaining traction is birth control.

CORRIGAN: So, it has great optics. We don’t have to use those bad poisons and the traps that are inhumane, so why not just, quote, give them the pill? But you have to get the birth control materials to large groups of mammals. And in cities, we have what’s called open populations of rats. That means you can have colonies living in sewers, rats living in parks, rats living in basements, rats living in subways. How do you get the birth control to all these colonies? Are you bailing out the ocean with a teaspoon, I guess is the best way to put it. 

So how do you keep down the rat population in a place like New York? The unfortunate answer seems to be that there’s no one clear solution. Part of the problem is that rat data is usually unreliable; this is frustrating for someone like Bobby Corrigan.

CORRIGAN: We haven’t addressed this issue in 300 years. We’ve looked at these rats just kill them, just put out poison, just trap them. No science has gone into this. But the compass is finally pointing in the right direction. 

What makes Corrigan say this, that the compass is pointing in the right direction? Well, last fall, New York City hosted the first-ever National Urban Rat Summit.

CORRIGAN: The credit here goes to Kathy Corradi.

Corradi is the new Citywide Director of Rodent Mitigation, a.k.a. the Rat Czar.

CORRIGAN: Within the first couple of weeks of being in the position of Rat Czar, we met for coffee and Kathy said, what if we bring in all the scientists from around the U.S. and even maybe around the world to talk about this issue? And from there, it took off. 

Like Bobby Corrigan, Kathy Corradi is both exterminator and appreciator. She knows the animal well. I asked her if she could explain the secret of the rat’s success in New York.

CORRADI: Yes, their fecundity is their superpower. Rats’ gestation period is about 21 days, you know, three weeks to a litter. You can have 8 to 12 pups in that litter. And then the females in that litter are ready to breed at about three months of age again. So, we just are talking exponential growth. And that is by design, evolutionary. They want to produce as much young as possible because they’re a prey species. The average life expectancy of a New York City rat — a wild rat, as we call it — is 8 to 12 months. If you take that same species in the laboratory setting, it’s about three years. It’s a tough life out there in the wild. So, the more offspring you produce, the better chance you have of passing those genes on. 

I spoke with Corradi shortly before the inaugural rat summit last fall. I asked her for a preview.

CORRADI: We’ve put together this summit to bring together the leading academic minds in this space, the researchers studying urban rats, and then different municipal leaders. So, we have folks joining us from Boston, D.C., Seattle. Everyone’s grappling with this. No city is like, you know what? We’re okay with what’s going on. 

The day of the rat summit arrived. Mayor Eric Adams helped set the stage. He began by praising Kathy Corradi.

ADAMS: I am so happy I have a four-star general who is working on finally winning the war on rats. We will make an impact and if we do so, we’re going to improve the health and the mental stability of everyday people in this city. So thank you for being here. Let’s be energetic. Let’s share our ideas. Let’s figure out how we unify against what I consider to be public enemy number one, Mickey and his crew.

And then the presentations got underway. Our friend Bobby Corrigan gave a talk called “Remote Rat Sensor Technology: Public Health Canaries in the Coal Mine.”

CORRIGAN: We can leave these sensors in place. They’re gonna work 24/7, 365. No benefits are needed. We’re not gonna pay them overtime, none of that. But they are giving us data. 

A rat researcher named Kaylee Byers gave a talk called “More Than Pests: Rats as a Public and Mental Health Issue.” Byers teaches at Simon Fraser University in British Columbia, Canada. She opened her talk by showing a global map of the rat’s reach. Only a very few places are spared — Antarctica, for instance, and a big rectangle in the middle of Canada.

Dr. Kaylee BYERS: “You might be looking at this rat map and saying, “Huh, what’s going on over here? This little blank space.” That’s Alberta, the rat-free province of Canada. We do actually have rats, there’s many fewer of them. But Alberta has marketed itself as the rat-free province.” 

And here’s the person responsible for keeping Alberta rat-free.

Karen WICKERSON: Karen Wickerson, I’m the rat and pest specialist for the province of Alberta. 

Wickerson was not able to make the rat summit, although she did visit New York not long after. We spoke with her in a studio.

WICKERSON: So I’m in charge of overseeing the program, which is provincial-wide. I coordinate response to rat reports, rat infestations if we have them, I work with people who are part of the rat patrol at the Alberta-Saskatchewan border. They check along the border twice a year, and they report back to me if they do find rats at all. 

Alberta is just over 250,000 square miles; that’s roughly the same size as Texas, where there are many rats. But Alberta says it doesn’t have a single “breeding population” of rats. Karen Wickerson gives some credit to the public.

WICKERSON: Albertans are very proud. I’ve had people go to great lengths to figure out how to report a rat sighting and they get a hold of me, and they say, “Oh, I know I’m supposed to report this, I want you to know I saw a rat at this location.” 

Wickerson told us she gets about 500 reports of rat sightings a year, but that only around 30 of them are legitimate. How can this be? Apparently, when rats are rare, a lot of people don’t even know what a rat looks like!

WICKERSON: If you’ve lived in Alberta your whole life, you probably can’t identify one when you see it. I can talk about the reports we receive of people misidentifying them as muskrats. They’re a larger rodent, have a waddle, long tail. We receive a lot of reports of them where people think they are rats. 

So what does it take to be, essentially, rat-free? Alberta has run a strict anti-rat program since the 1950s. The Norway rat was migrating then in great numbers from the eastern part of Canada, and farmers out west saw the potential for crop damage.

WICKERSON: Because of the damage they could cause, they declared them a pest. Being a pest, an agricultural pest, in Alberta means that every Albertan, is required to control them.

Among rat people, Alberta is famous — the way Pine Valley is famous among golf people, as a remote and sanctified place, almost too good for this world.

WICKERSON: People are desperate, and they want to know what our secret is. I always say, like, we’re at such an advantage because the program started right when rats arrived to our boundary. We prevented them from spreading into the province and establishing. So for me to comment on populations now that do exist, you know, it’s hard for me to really give advice. I would say that public education is always critical. It’s challenging. I do really feel for people in other jurisdictions. 

So how did Karen Wickerson enjoy her visit to the super-ratty jurisdiction of New York?

WICKERSON: I found it fascinating because I don’t see rats on the street in Alberta. So on my first night, I was walking out for dinner, and I have to say, I was delighted when I saw a rat munching on a bag of garbage.

As a New Yorker, I am of course proud that we keep coming up with new ways to entertain visitors. But: we should talk about the garbage.

Jessica TISCH: We dump all this trash on our curbs, and we sit around, and we wonder why we have a rat problem.

* * *

When we first set out to make this series on rats, we were inspired by what you might call a foundational text: a book called Rats: Observations on the History and Habitat of the City’s Most Unwanted Inhabitants, by Robert Sullivan. I remembered reading an excerpt of the book in The New York Times Magazine when it was published, in 2004; and then recently, a dear old friend of mine died, and I inherited some of his books. Rats was one of them. My friend, Ivan, was the kind of reader who likes to underline interesting passages of a book as he goes. When I sat down to read his copy of Rats, I found that roughly half of it was underlined. That’s what I told Robert Sullivan when I called him up.

Robert SULLIVAN: What a lovely thing to hear. So, yeah, it’s tough to be known as a rat guy. But then right after that, it’s good to be known as a rat guy.

I asked Sullivan to introduce himself, for the recording.

SULLIVAN: My name’s Robert Sullivan, and I write things. 

And I asked for a bit more detail: 

SULLIVAN: My name is Robert Sullivan and I write books and magazine articles, and I write about places that maybe people haven’t looked at, or I try to look at places differently from maybe how they’ve been looked at.

DUBNER: So you have written a lot of articles, several books. Are you still best known for Rats, do you think?

SULLIVAN: The idea that I’m best known for anything is an idea I struggle with.

DUBNER: Hey, you won a Guggenheim. 

SULLIVAN: I did. It’s not clear — they could have been thinking of another Robert Sullivan.

I asked Sullivan to explain how he had come to write about rats.

SULLIVAN: The concrete reason was, I was on a reporting job. I was covering a whale hunt for The New York Times Magazine. I was out on a reservation, the Makah Nations Reservation, out at the very tip of the United States of America, the continental United States and Pacific Northwest. And people were there to protest the hunting of whales. 

DUBNER: And this was a Native American tribe that had kind of a grandfathered-in license to hunt them? 

SULLIVAN: They had it in their treaty rights. There were people on the reservation who believed that maybe we shouldn’t hunt whales right now. There were also people who thought they should. There were also people who thought that whether they should or they shouldn’t was a moot point because it’s a matter of tribal sovereignty. And this was an incredible thing to be witness of, this debate and this action. While I was there, I met a bunch of people who were working for animal rights groups. And one of them said, “I’m not going to be here tomorrow for the protest, I’ve got to go back to Seattle, got to go back to our offices.” I asked why. They said, “Because we have pest-control people coming.” And I said, “Well, what are you doing?” And they said, “We have rats.” I said, “Are you going to trap and release them or what?” Because I just figured. And they said, “No, they’re rats, we’re going to have the exterminator take care of them.” It just suddenly dawned on me, in my abstract pursuit of where is the division between what we think of as natural and not natural, that this was a line in the philosophical sand.

 So that’s what led Robert Sullivan to write about rats. But it’s the depth of the reporting and thinking and writing that makes his book spectacular: it is brash and clever and interesting on every page. I can see why Ivan couldn’t stop underlining. The book feels like a cross between punk anthropology — or rodentology, I guess, but there’s a lot of anthro in there — and cheeky encyclopedia. “Rat-control programs,” Sullivan writes, “are like diets in that cities are always trying a new one. In the city, rats and men live in conflict, one side scurrying from the other or destroying the other’s habitat — an unending and brutish war. Rat stories are war stories, and they are told in conversation and on the news, in dispatches from the front that is all around us.” I asked Sullivan what he thought of New York mayor Eric Adams’s war on rats, and the recent rat summit.

SULLIVAN: Typically I try to ignore what mayors say about rats.

DUBNER: He was indicted not long after. Do you think that was a coincidence, or no? Do you think the rats have the pull to make that happen? 

SULLIVAN: I think that the history of rat control in New York City and many cities is aligned with the history of mayors wanting to get attention for being great and taking care of things. Just starting way back, Mayor Lindsay gave out metal garbage cans. Mayor Dinkins built housing — very effective way to help with rat problems. Mayor Giuliani took trash cans off the streets in Harlem, it’s a kind of tributary I guess of the broken windows theory that says if you take trash cans off the street, people won’t throw trash on the streets. Mayor Bloomberg is the rat data guy. He was all about, where the data is for rats, like where rat bite reports are — which is a complicated statistic. 

DUBNER: Why? 

SULLIVAN: Because people who are getting bitten by rats might not report them, might not have the wherewithal or the, frankly, resources to go about doing that. And so Adams is going to kill them by drowning them in beer or whatever he does — like, it’s just brutal war on rats and a take-no-prisoners style.

When Sullivan talks about Eric Adams “drowning rats in beer,” he’s referring to an idea that Adams promoted in 2019, when he was borough president of Brooklyn. This involved an Italian rat trap called an Ekomille. It is baited with nuts or seeds; a rat, upon entering, drops through a trap door into a vat filled with a green, alcohol-based solution. Say what you will about Eric Adams as an elected official — he’s got a lot of problems at the moment, and by the time you hear this, he may have been shoved out of office — but he could never be accused of flip-flopping on rats. Shortly after he was elected mayor, in 2022, he signed into law a Rat Action Plan. It included four key components: rat-resistant trash containers, more timely trash pickups, the creation of “rat mitigation zones,” and a crackdown on rats around construction sites. Here’s what one city council member said at the time: “Today, we declare that rats will no longer be the unofficial mascot of New York City.” This Rat Action Plan of course required a rat czar — in the person of Kathy Corradi. She explained that a major focus of the plan is cutting down the rats’ food supply.

CORRADI: What we’re effectively doing is making their lives more stressful, and cutting off their super-power to breed. There’s a whole 99-page report about how we’re going to do that, because — again, simple things are complex when we talk about the density of New York. For a long time, New York City, before we were known for our black bags on the curb, we were known for our steel trash cans on the curb, as made famous by Oscar the Grouch.

OSCAR THE GROUCH: Oh, I love trash!

CORRADI: So, the can he sits in was ubiquitous to New York before the plastic bag. 

If you’ve never visited New York City, it may surprise you to learn that most trash is simply left out for pickup on the sidewalk in big plastic bags. As Corradi says, trash used to be put in metal cans with lids. During a sanitation strike in 1968, those cans overflowed with tons of loose trash — and newly invented plastic bags came to the rescue. Plastic was also quieter and much lighter, which made the returning sanitation workers happy. There was just one problem: rats had an easy time chewing through the plastic. So what’s the new plan?

CORRADI: We’re moving towards containers, which means basically a garbage can with a secure lid.

These new containers are also made of plastic, but a much thicker grade than the flimsy bags.

CORRADI: And as of November this year, 2024, there’ll be different administrative code and legislation in place that 70 percent of New York City waste will be back in containers.

And here’s the person who can tell us more about that.

TISCH: My name is Jessica Tisch. I am the New York City Sanitation Commissioner.

That’s what Tisch was when we spoke, a few months ago. She has since become commissioner of the New York City Police Department. The previous one resigned in the midst of a federal investigation; the one before that resigned after clashing with the mayor. Like I said, the Adams administration has been a mess. In any case: when Jessica Tisch was running Sanitation, she understood just how important that job is.

TISCH: Sanitation is the essential service in any city, but particularly in New York City. Every day, we leave 44 million pounds of trash out on our curbs. And from my perspective as a lifelong New Yorker, New York City hasn’t really changed the way we manage that trash in decades. For the past 50 years, we have been leaving our trash out on our curbs in black trash bags. It looks gross. In the summer, it smells gross. One third of the material in those black bags is human food. And unfortunately, human food is also rat food. So we dump all this trash on our curbs, and we sit around, and we wonder why we have a rat problem. The single biggest swing that you can take at the rat problem in New York City is getting the trash bags off of the streets. And that is what we have set out to do. We don’t want the bags on the streets. Instead, we want our trash in containers. Most cities around the world have been containerizing their trash for decades. New York City is not going to be the first city to do this. In fact, we are definitely going to be one of the last. This is long overdue. And it works everywhere else. 

Okay, so let’s get into the details. Smaller buildings and single-family homes will have their own bins.

TISCH: We have developed, I would say, a gorgeous new standardized New York City official wheelie bin. A lot of people laugh at us because they think we sound like we have discovered the wheelie bin. We acknowledge that we have not. Nonetheless, we have a standardized wheelie bin now in New York City that all 1 to 9 unit residential buildings will be required to use.

And how about bigger buildings?

TISCH: You would need in those buildings too many of those wheelie bins, it would become unwieldy. So instead, for those large buildings, we are going to put large, fixed, on-street containers. These containers are about four cubic yards. The bins do take up parking spaces, but because they are being used just for the large buildings of 30 units or more, it’s not as big a hit to parking citywide as you may otherwise expect. We estimate that it’s about three percent citywide.

These new large, on-street containers will also require new garbage trucks. 

TISCH: Sanitation workers cannot lift these four-cubic-yard containers. In the United States, we didn’t have a large, automated, side-loading truck that worked in cities. And so we developed that truck with some vendors who do work in Europe, And we rolled out the first of these automated, side-loading trucks that are going to hoist these four-cubic-yard containers.

If you’ve ever seen garbage trucks in Germany or Singapore or — well, a lot of places — the sight of a New York City garbage truck extending its claws to lift and dump a big trash can may not impress you. But here, it’s a big deal. The program is currently being piloted in a few uptown neighborhoods, including Harlem. When someone posted a video of the truck in action on social media, the Sanitation Department retweeted the video, with a message: “This was our moon landing.” Now, before we go making fun of New York City for what some people might consider an overstatement, let’s consider this: trash tech is one thing to get right; trash behavior is another. Jessica Tisch realizes this. 

TISCH: Change is hard, I think generally. Having worked my whole career in city government, I see that. It’s a change that affects all 3.5 million residences in New York City, all 8.3 million New Yorkers, and all 200,000 businesses. Taking out your trash is something you do every day. So now by containerizing it, we’re asking everyone in the city to change the way they do something.  

And that’s not the only behavior change to worry about. Back on the street, with Bobby Corrigan, we still haven’t seen a rat but on a nearby park bench we do come across signs of recent human activity — a discarded wrapper, from a raisin cake.

CORRIGAN: This is classic right here. Someone just came recently. They sat down to have their little snack. Human beings — I don’t know, but what I’ve read is 20 to 25 percent of us as a species, we do that behavior. That 20 to 25 percent is all the rats need, probably it’s triple what they need. The rats that live here will come out and say, Well, how much was left in that wrapper? And the answer is enough for them tonight. We can’t have this behavior, but we can’t get away from it. No matter what posters you put up — please don’t litter, please do your trash right — human beings, some don’t care. Leave me alone.

Further down the street, we come across a bank of the new trash containers for big buildings. Corrigan is impressed.

CORRIGAN: So this is a very smart thing for a city to do, is what we see here with this new bank of containerization, that instead of leaving bags on the curb, they get put into a bank. The key thing is to make sure that if a car hits this or dents it or breaks it — that’s going to be expensive, right? So everything’s going to have its pluses and minuses. 

Actually, everything about New York’s new trash plan is expensive — the new bins, the new trucks, the new vigilance.

CORRIGAN: Long-term sustainability, this is going to save hundreds of millions of dollars for a city. This is the most environmentally smart thing you could do, the most humane thing you could do. If the rats want to move on to some other place, go for it. 

That’s a nice thought, in theory at least — that New York City’s rats will just move on to some other place if their food supply is constrained. But first, there needs to be evidence that the new containerization plan is actually working. The other day, walking down the street, I came across a few of the new wheelie bins that Jessica Tisch is so excited about. They were lying on their sides, the lids broken off the hinges — and, if I were a rat, I would be excited. What do we have here — Shake Shake? Luke’s Lobster? Maybe even Per Se? There have also been reports of rats chewing through these supposedly rat-proof trash bins. In a recent interview, the president of New York’s sanitation workers union, said, “Things that work throughout the country don’t work in New York. New York is New York. It’s its own thing.” Now, given his position, he may be sending a message: because the more you automate trash pickup, the fewer jobs there will be for sanitation workers. Is a rat-free city even possible?

Ed GLAESER: It’s clearly possible that you can have an urban area without rats. But they do love it there. 

* * *

We heard New York City rat czar Kathy Corradi say that by the end of 2024, some 70 percent of the city’s trash was no longer being placed in flimsy plastic bags, but rather in sturdy plastic bins.

CORRADI: The goal is 100 percent.

DUBNER: What’s the timeline for that?

CORRADI: We’re waiting to, kind of, play out these pilots and see what the feedback is, what’s the best technology that works. Rats do not care about jurisdiction. So we need to think about how we do this work as a whole-of-city approach. 

That whole-of-city approach will still include some poisons — or “treatments,” as Corradi calls them.

CORRADI: Some of our, quote, more sexy treatments rat ice is one of them. That is dry ice, it off-gases carbon dioxide and that asphyxiates the rats right in their burrows. We also use a technology called BurrowRx. Similar idea: it off-gases carbon monoxide, the rats asphyxiate in their burrow. And a new technology that’s come out in the last couple of years is a canister of carbon dioxide — same application. The difference with that is we can measure how much gas is flowing out of the tank. We can actually use that in closer proximity to buildings, which is really important in a dense city like New York. 

And how about the rat birth control that we discussed earlier, with Bobby Corrigan.

CORRADI: Most of the birth control contraceptive that’s on the market for rats requires a constant feed, meaning they have to feed on it over and over again. And if we have food competition, that becomes a challenge.

DUBNER: So, the mayor who appointed you, Eric Adams — this administration is turning out, especially in recent weeks as we speak, to be one of the most problematic, potentially corrupt administrations recently. All sorts of investigations, seizures of cell phones the resignation of the police chief, and so on. What’s it like to be representing a city agency — like you are now — with all that storm going on around? I’m just curious, from the personal perspective, of how hard it makes your job?

CORRADI: You know, we have a job to do, and I come to work every day committed to doing that. The immense responsibility to do this well for the city that I love, for all the people who live in this city and feel such a heavy impact from it that’s the focus.  

DUBNER: I could also see that because of your job and because of how much people care about rats, I could imagine if you do this well, that you are mayoral material. Is that an ambition?

CORRADI: No, I’m just focusing on serving the public. I was out twice this week — once in Brooklyn, once in downtown Manhattan — walking with groups, talking about rats. I’ve held folks’ hands, as they’re tearing up about rats that are in their homes. And then on the other side, you know, folks who are inventing their own devices to keep rats out of their property. That’s what I love. I love this city. I love our ingenuity — our human ingenuity and our rat ingenuity. And that’s what keeps me fired up about this work.

So how are Corradi and her colleagues performing in the early days of this war on rats? As she told us in part one, the science of rat measurement is not very sophisticated; there is no reliable rat headcount. So the metrics she uses are a bit removed — rat complaints called in to the city’s 311 line, for instance, and rat sightings in the new mitigation zones. Those numbers are down; but: much more data is needed. And: there’s a potential countervailing force: a new research paper by a large team of biologists and pest-control experts argues that climate change is contributing to the rise of the rat population in New York and other big cities. So maybe the rat will remain our “unofficial mascot.”

GLAESER: It’s clearly possible that you can have an urban area without rats. But they do love it there.

That’s the Harvard economist Ed Glaeser; we heard from him in part one of this series as well; he is an expert in, and huge fan of, cities. And he grew up in Manhattan. I asked Glaeser what he thinks of the city’s Rat Action Plan.

GLAESER: Impacting the food supply seems sensible, though that requires New Yorkers to be very attentive about their trash, which is not something I remember all New Yorkers being. But perhaps that can be managed.

DUBNER: I don’t know how much time you’ve been spending in New York lately, but there has been a wholesale change, which is the conversion l from plastic bags of trash that you just throw out onto the sidewalk and wait for Sanitation to come pick up, which plainly doesn’t seem very rat-proof — in fact, it’s not at all — to a requirement that trash be contained in plastic bins with a top. It seems pretty darn sensible and indeed easy. 

GLAESER: I agree with that. That sounds perfectly reasonable. Although you’re still depending upon the New Yorker actively, like shutting the plastic bin and keeping it effectively closed.

DUBNER: Now, what about you, Ed? If you were rat czar, in addition to changing the way food is disposed of, what other solutions might you think about?

GLAESER: Well, I would, of course, start with something like measurement. One article I saw about this, that Hong Kong seems to be doing a lot with heat vision things. So, they’re looking at the rats moving around at night. I imagine you could do that with some combination of drones and satellite in a way that would give you an effective idea of where the rat hot spots are.

DUBNER: Why would measurement be important for you? 

GLAESER: Because I want to know whether whatever I’m doing is working. So these things might be right, but without measurement, who knows? And I think, you know, in everything where there’s a problem and you don’t feel like you’ve seen a solution that’s been tried 50 times, that always works, the first thing is to start with the humility to learn. You know, let’s try the trash cans and let’s see if the rat density goes down sufficiently in this region. Presumably they should be compared with the traditional poisoning method.  

DUBNER: As far as we can tell, there’s not really been any kind of decent rat census. Why do you think that is? Is it that hard? 

GLAESER: I think it’s pretty hard because a lot of them are indoors. Even if you could have, you know, drones full-time on every alleyway in the city at night, that’s not going to give you a full measure. And you don’t even know if like you’re seeing a rat at 1:00am and a rat at 3:00am are the same rats or not? Are you actually going to know that?  

DUBNER: There was one solution we didn’t touch on, one potential solution, which has been tried before — I believe in Egyptian cities in the old days used this — which is just armies of cats. Do you like that idea?

GLAESER: So, Sullivan claims that cats can’t take down a fully grown rat. In which case you need terriers. Having enough terriers to take on — if you thought, let’s say we were at two million rats in New York, that’s a lot of terriers. And it’s not like dogs don’t potentially carry diseases as well. I’m always worried about introducing large numbers of some other species to get rid of one species. One thing we haven’t talked about is the eating of rats. There is at least some tradition in parts of China for eating rats. That strikes me as being an enormously sensible thing, somewhat similar to the East Asian practice of selling nightsoil. So both Chinese and Japanese cities engage in the practice of basically selling their human excrement to farmers in nearby areas. And that created a very virtuous circle where the farmers had better land, and the excrement got removed. Dealing with the problem by turning it into something that’s desirable — like, you know, food, that seems kind of good. Now, most of the time in the West, we haven’t been able to stomach it. But that strikes me as a thing to potentially think about. 

DUBNER: Yeah, I read now the rats that are currently eaten in China are often the bamboo rat, says they’re specifically bred for consumption. An estimated 66 million raised annually in China. You don’t happen to know how a bamboo rat tastes versus a Norway rat, do you?  

GLAESER: I do not know. I have never eaten either kind of rat, but I would happily eat a bamboo rat in Fujian if I were there. 

DUBNER: What about eating a Norway rat in New York, if prepared well? 

GLAESER: If prepared well, sure, I’m open.

GLAESER: Is someone actually serving Norway rat? 

We did look around to see if anyone in New York City is serving rat. We checked in with a restaurant where, for another episode, I once ate a bunch of insects. Which were delicious. But they had shut down. We could not find rat on a single restaurant menu in New York City. We also wrote to some private chefs; I figured they get unusual requests all the time. But no luck there either. Here’s how one chef replied: “Unfortunately, I am not able to source this for you. However, I would be happy to cook for you and your guests a beautifully constructed dinner using squab.” We passed on that; squab is too easy.

CORRIGAN: I have eaten rat. But I’m going to tell you that I cheated.

That, again, is Bobby Corrigan, the urban rodentologist. We’re still huddled with him outside, in an alleyway.

CORRIGAN: And the way I cheated is, I have a friend who works in a laboratory studying drugs and pharmaceuticals, and they use it on rats. So I just said, can you bring me a rat? So I ate a laboratory rat. But it’s the same species. It’s the same muscle tissue. It’s the same everything. So technically, did I eat rat? Yes. Did I eat Norway rat? Yes. But did I eat wild Norway rat off the streets that may have come out of a sewer? I would be very dumb to do that. It’s full of internal worms, virus — you know, it’s disgusting. I would never. You’d be dumb to do such a thing.

Our next question for Corrigan was — well, you know the next question. Did his rat taste like chicken?

CORRIGAN: Yes — but here’s the thing. All mammal muscle tissue, right, it’s not that different.

 Standing in the cold with Corrigan today, we’re not hoping to eat rats, we’re still just trying to spot one. So far on this tour, we’ve seen plenty of A.R.S. — active rodent signs — but no active rodents. Corrigan still has faith.

CORRIGAN: I would put it at about 50-50 that we’re going to see at least a couple of rats.

 We head over to a small park in Tribeca.

CORRIGAN: Rats love parks because the Norway rat is actually from Mongolia, and in Mongolia, their life was to burrow into the soil of the fields of Mongolia. So their brain says, get into the earth, right? Geotropic positive, get towards the earth. Squirrels are geotropic negative, climb trees away from the earth. So it’s a situation where parks, if the soil is healthy — which it has to be for a park to keep the plants growing — the rats get down, they’ll dig a hole. You’ll see a hole, probably. We’ll find one here shortly.

We do find a hole. And then another, and then four more — six burrow holes in one small area of one small park.

CORRIGAN: Rodents are really great examples of, work hard and you’ll be successful, right? So these animals, they’re constantly digging in soil, constantly constructing burrows, constantly seeking food you know, they get it done. And so when people say it’s so hard to get rid of rats, it’s like, that’s right! Because you’re up against a hardworking, intelligent, small rodent that we don’t appreciate enough. I’m constantly thinking, you know, we could actually do things like rats a little bit more, as crazy as it sounds, and our species, Homo sapiens, would be better for it. 

It’s late afternoon by now, starting to get dark, and we give up without having spotted a rat. Does this mean New York City’s rat problem is getting better? Maybe, but maybe not. The Norway rat is primarily nocturnal.

CORRIGAN: When this city goes quiet, that’s rat time. It’s like, when you’re inside buildings and they’re in the walls, how do they time their time to come out? When the plumbing stops. So when people get ready for bed and they brush their teeth and they use the showers and then all of that stops in the building, that’s their time. When it starts up again in the morning, it’s back to bed.

It does make you wonder — just how much of our war on rats is a war against some part of ourselves?

CORRIGAN: Animal behaviorists will say, you know, when we do study rat colonies, we’re studying ourselves. It’s very true. When you put rats under stress, they get aggressive. We get aggressive under stress. What causes people to, you know, be happy, be sad, be anxious. All of those things play out in the rats as well.

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Freakonomics Radio is produced by Stitcher and Renbud Radio. This series is being produced by Zack Lapinski with help from Dalvin Aboagye. We had recording help this week from Neve Jahn and Digital Island Studios. The Freakonomics Radio Network staff also includes Alina Kulman, Augusta Chapman, Eleanor Osborne, Ellen Frankman, Elsa Hernandez, Gabriel Roth, Greg Rippin, Jasmin Klinger, Jeremy Johnston, Jon Schnaars, Morgan Levey, Neal Carruth, Sarah Lilley, and Theo Jacobs. Our theme song is “Mr. Fortune,” by the Hitchhikers; our composer is Luis Guerra.