Even with a new rat czar, an arsenal of poisons, and a fleet of new garbage trucks, it won’t be easy — because, at root, the enemy is us. (Part two of a three-part series, “Sympathy for the Rat.”) SOURCES:Kathy Corradi, director of rodent mitigation for New York City.Robert Corrigan, urban rodentologist and pest consultant for New York City.Ed Glaeser, professor of economics at Harvard University.Robert Sullivan, author of Rats: Observations on the History and Habitat of the City’s Most Unwanted Inhabitant.Jessica Tisch, New York City police commissioner. RESOURCES:"Increasing rat numbers in cities are linked to climate warming, urbanization, and human population," by Jonathan Richardson, Elizabeth McCoy, Nicholas Parlavecchio, Ryan Szykowny, Eli Beech-Brown, Jan Buijs, Jacqueline Buckley, Robert Corrigan, Federico Costa, Ray Delaney, Rachel Denny, Leah Helms, Wade Lee, Maureen Murray, Claudia Riegel, Fabio Souza, John Ulrich, Adena Why, and Yasushi Kiyokawa (Science Advances, 2025)."The Next Frontier in New York's War on Rats: Birth Control," by Emma Fitzsimmons (New York Times, 2024)."The Absurd Problem of New York City Trash," by Emily Badger and Larry Buchanan (New York Times, 2024)."Mourning Flaco, the Owl Who Escaped," by Naaman Zhou (The New Yorker, 2024).Rats: Observations on the History & Habitat of the City's Most Unwanted Inhabitants, by Robert Sullivan (2005). EXTRAS:"The Downside of Disgust," by Freakonomics Radio (2021)
Chapter 1: What are the challenges in New York City's war on rats?
Sometimes we go to war with our neighbors, and sometimes those neighbors are rats.
Okay, so we're outside in New York City looking at what we call active rodent signs, or ARS.
That is Bobby Corrigan. He is an urban rodentologist, a former rodent researcher who now works for the city of New York.
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.
And that's because the rats nearby got below the sidewalk, tunneled into this area, dug out the soil so they could 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?
Just five feet away, we have the proverbial catch basin that the stormwater 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?
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Chapter 2: Who is Bobby Corrigan and why is he important?
Wow, I didn't realize we were going to get so many people showing up to talk about rats.
We will hear about some battle tactics.
An ounce of prevention is worth a pound of cure.
But what if it's too late for prevention?
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.
You know, birth control on paper sounds pretty darn smart, right?
And we will consider some other ideas. 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.
This is Freakonomics Radio, the podcast that explores the hidden side of everything with your host, Stephen Dubner.
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Chapter 3: Why is rat poison a controversial solution?
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.
So it has great optics. You know, 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 is no one clear solution. Part of the problem is that rat data is usually unreliable. This is frustrating for someone like Bobby Corrigan.
We haven't addressed this issue in 300 years. We've looked at these rats as 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.
And 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. You know, the credit here goes to Kathy Karate. Karate is the new citywide director of rodent mitigation, also known as the Rat Czar.
Within our 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.
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Chapter 4: Can rat birth control be an effective strategy?
We can leave these sensors in place. They're going to work 24-7, 365. No benefits are needed. You know, we're not going to pay them overtime, none of that. But they're 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.
You might be looking at this rat map and saying, oh, 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 a person responsible for keeping Alberta rat-free.
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.
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 animals. 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 does not have a single breeding population of rats. Karen Wickerson gives some credit to the public.
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.
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Chapter 5: What role does Kathy Corradi play in rat mitigation?
So the can he sits in was ubiquitous to New York before the plastic bag.
If you have 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 Karate 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?
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. 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.
My name is Jessica Tisch. I am the New York City Sanitation Commissioner.
That's what Tish 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 Tish was running sanitation, she understood just how important that job is.
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.
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Chapter 6: How has Alberta managed to remain rat-free?
What's the timeline for that?
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 Karate calls them.
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, a 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 we discussed earlier with Bobby Corrigan?
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.
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 issues. 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.
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