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TRANSCRIPT
Wartha: I’m actually quite scared to go down.
Charli: Oh my goodness. I’m scared as well.
Wartha: Do you smell it?
Charli: Yeah. It’s stinky.
Deep in the basement of an apartment building in Berlin’s south lingers a stench that’s hard to forget.
Wartha: *audible shudder*
Wartha: This is my basement. Or, our communal basement. You can come in...
Charli: My god, it’s really quite intoxicating. *cough*
The scent is heavy. Pungent. Asphyxiating.
Wartha: As you can see there’s a lot of poop.
Coupled with small, dark droppings, a slick, black greasy slime and small, jagged holes, it can only mean one thing:
Charli: I feel like I can’t breathe.
Rats.
News montage – rats on the rise in cities around the world
Despite centuries of our dogged efforts to get rid of them, rats still live among us – sometimes awfully close. Not only that, in many cities, they’re multiplying1. From Berlin to New York to Toronto – it appears rats aren’t just surviving; they are thriving. So, what’s going on? Are rats taking over... or... are they showing us something about the way we live? I'm Charli Shield. Today on Living Planet: what urban rats can teach us about our cities, our habits, and the systems that keep them coming back.
Wartha: I see them sometimes if I go out to throw away trash. They run around here and you can hear like scratching within the bins and then there are like opened up, ripped up bags.
We’re starting this episode in Neukölln, in the south of Berlin, where my friend Wartha rents a flat on the third floor of an apartment building built the 1940s. And, where a colony of rats appears to have moved into her basement.
Wartha: As you can see these windows lead to the basement. The lower windows. And I assume that the rats can just access the basement through these windows, and maybe they actually live here.
Wartha hasn’t actually been down here for nine months. The last time she got a fright.
Wartha: One rat actually crossed my foot, like, ran over my foot.
She has sought help to get rid of them.
Wartha: The pest controller came by and he said that not only our street but also the other streets have a rat problem and that it doesn't really make sense to put in rat traps that they would eat whatever is out there instead of what is put in the rat traps to kill them. And there's also a problem with the sewage system...
Wartha’s predicament is not unique in Berlin. About 3.5 million people live in Germany's capital2. Alongside them, in a great many nooks and crannies, burrows, buildings, drains and sewers live many, many rats. They scuttle along the tracks in the underground, dart in and out of the bushes at the park and inhabit the trash cans, and the plastic bags discarded on the curb. It’s almost impossible to estimate how many rats live in any one city – they’re nocturnal and they breed like mad. Estimates range from hundreds of thousands to millions.
This got me wondering: What exactly is fueling “the rat problem”? And could there a better way to manage the human-rat relations, or is this it? To find out, I needed to look beyond this basement, and beyond Berlin.
Bobby: ‘Ok, we’re recording over here...’
Bobby: My heart was pounding. I was nervous. I was scared. I didn't know what was about to happen, you know, living with rats. Will they attack me? Will they bite me? Will they reject me?
When you start researching ‘rats in cities’, it only takes a couple of clicks before you see this one guy’s name pop up.
Bobby: Bobby Corrigan.
Bobby Corrigan.
Bobby: And literally I moved in, I brought my camping gear, my sleeping bags, my food...
Bobby is an ‘urban rodentologist’.
Bobby: That's a scientist that studies city rats and mice.
A job he’s had for 43 years. And as you can hear, he’s taken it seriously from day dot.
Bobby: ...and I lived with the rats. When they were asleep, I was asleep. And when they were up, I was up making all kinds of observations.
Bobby is talking about living with rats in barns in Indiana, outside Purdue University where he studied. Back when he first started studying rodents, which he came to do almost by complete accident, he told me, Bobby co-habited with rat colonies in these barns for weeks on end, trying to get to know them. And although when he moved in he was petrified, once both the rats’ and Bobby’s nerves were settled, they got on quite well.
Bobby: Nothing happened other than I was able to watch them. They looked completely... skittish of me was the best term. I would approach, they'd run away, they'd squeak, they'd approach closer the next time and run away.
Gradually, Bobby faded into the background.
Bobby: Pretty soon, you know, they accepted me is the term I'll use. I don't know if they ever did or not, but they certainly weren't aggressive towards me and they weren't afraid of me. So after a while I was able to feed them by hand. They would come closer and closer and pretty much the colony seemed to... I, you know, become normalized. They seem to be like, okay, we have a new guy here, this guy Bobby, that's hanging out with us. He's not doing us any harm. And I started taking notes. After a while, they tended to ignore me and I watched them interact with each other. And I wasn't sure what I was seeing all the time. For example, I saw rats being kind to each other.
He watched rats groom each other, play, wrestle, and deliver food to sick or elderly rats. He also watched ‘bully’ rats attack others for no apparent reason.
Bobby: And I'm like, was I imagining that? Was that real? You know, has this been published? Has anyone studied these things? And some of those behaviors weren't published at the time, but now they have been in good journals, refereed science journals. And we do know that rats have the same emotional drives as human beings do. Happiness, sadness, depression, caution, you know, all of that. You know, they're mammals just like we are. And of course, you know, psychologists would probably say, you know, that's no surprise at all. The mammal brain is the mammal brain, whether it's whales or humans or bears or rats.
Often, Bobby had the feeling he was watching a furry human colony from above, he said.
Fast forward to now and Bobby has long been teaching ‘rodent boot camps’ and leading ‘rat safaris’ through New York City.
Bobby: I call them rat safaris cos that’s what they are!
Yes – people want to go on those.
Bobby: At night, that’s their world... They are nighttime creatures. And usually from dusk til two hours afterwards is your best chance to see rats doing their natural thing.
Bobby: I usually take safaris out of lower Manhattan. It's down on the southern end facing the Statue of Liberty. The reason for that choice is it's among the oldest portions of New York City. And what that means is the sewers are very old and there's probably channels below that city that we don't even know about.
Channels that we don’t know about, but that the rats who live in New York certainly do.
Bobby: And the interesting thing there is the rats, they were deposited onto US shores through European ships, as best as we know, probably in the early 1700s. And they start establishing tunnels and pathways all the way back then that to this day, some of them still exist.
The rat species that rocked up with the European colonizers was the brown rat, which originated in current-day Mongolia and northern China. It's the most common species today – the one you’re most likely to find rifling through your trash or scurrying about in the bushes. The second most common is the smaller, sleeker black rat, which has been traced back to Southeast Asia. And these urban rat species are just about the most successful species on the planet – having established themselves on every continent bar Antarctica.
Bobby: Over thousands of years, you know, with humankind, they started getting on their wagons as they started traveling about. And pretty soon the Silk Road and avenues westward and ships and the rest is history. As we started developing transportation, they ended up the globe over.
Part of why urban rat species have been so successful is because they’ve figured out how to live alongside humans – Earth's other dominant species – very successfully.
Bobby: They're called commensal rodents in the literature, which means to share the table. And we don't do that willingly, but we use that term because through eons of time, they're constantly getting to our food that we want to eat and share it. So, but they're competing with us in that regard. And the other word that's kind of cool is a word called kleptoparasitic. We all know what parasites are, and kleptoparasites... So a kleptomaniac is someone that constantly steals things. Well, the rats are kleptoparasitic on us, they’re always stealing our food.
Rats have always been incredible breeders. Under ideal conditions, one pair of rats can produce 1000 offspring within a year. And those ‘ideal conditions’... are often in cities. Where there are more and more humans with which to share the table and steal from. Especially nowadays.
In 2025, Bobby and a global team of colleagues published a paper in Science Advances showing urban rat numbers were on the up in major cities from New York to Washington to Amsterdam6. They found that as cities are expanding over larger areas and human population density increases, rat populations are increasing, too.
Bobby: And so it's about food, it's about urbanization, and it's about people density. As we increase our ways, the rats are going to benefit from that.
And they found something else as well: a link between cities getting hotter from climate change and rapidly rising rat populations. They think that's because shorter winters mean longer breeding seasons for rats – who, as we’ve covered, can get a lot done in a short space of time. And, there tends to be more food available during warmer months.
Bobby: And so when you multiply that by millions of small mammals like rodents, you end up with, of course, this incredible algorithmic growth in an area where the world over as a consultant, I can tell you, I get calls saying, can you come to our city because we are seeing rats like we've never seen before. And that's been a gradual thing that caught us by surprise over the past decade of a slow, slow simmer leading to, like we know, eventually a boil over. And that's what's going on.
In many ways, rats are loving this brave new world we’ve engineered for them.
But, apart from being universally disliked, what threats do rats actually pose to humans...? Well, they can carry diseases – like leptospirosis, hantavirus pulmonary syndrome, and the bubonic plague. They also like to chew through electrical wiring – because, Bobby says, to them it looks like a plant – and they can cause infrastructure damage, destroy our belongings, and they can invade and contaminate food manufacturing, storage and processing. Research has also shown people living with rat infestations have poorer mental health.
So, though Bobby doesn’t think the vitriol thrown at rats in our culture is really justified, he does argue that, for public health and safety, we do need to keep them at bay.
Bobby: People feel like they can do anything to kill a rat and it's okay. But in my opinion, it's not okay. It's another mammal, but nevertheless, we do have to manage them out of our cities, so they don't bring us any disease or germs.
This brings us to rat ‘management’ methods. And why many of them fall short.
The most common rat control methods involve lethal poison and traps. Back in the 1980s, a rat poison called ‘second generation anticoagulant rodenticide’ was invented, after pest controllers realized rats had developed an immunity to the first-generation stuff.
Old commercial: "When getting rid of rats and mice is almost as easy as saying ‘disappear’. Here’s how it works...”
Bobby: And not to get technical, but they just simply, you know, made them more powerful.
The poison basically works by causing rats to bleed to death.
Bobby: Well, it seemed terrific. Like, well, no more resistant rodents to the new generation of poisons.
Until...
News clip: “A controversial rat poison is coming under scrutiny for killing wildlife...”
Bobby: Well, now 40 years, 45 years later, we realize that those animals, if they're eaten, say by a hawk or an owl or a bobcat or a fox, you know, if they are consumed by almost any other carnivore or a bird, in turn, we're poisoning those animals through secondary toxicity when they eat today's current rat poisons, if they're the anticoagulants. So here we are in furthering damage to the balance of earth by putting out poisons that we're thinking were killing only rodents when in fact, we're killing other mammals.
And in addition to the fact these can be cruel and bad for biodiversity at large, centuries of trying have shown us that trapping and poisoning rats is just not all that effective, while being expensive. Cities are still crawling with rats.
So... what could a more effective and sustainable alternative to poison be?
Experts like Bobby advocate for prevention rather than poison. And that starts with paying attention to something we do every day...
Bobby: When people ask me, what do I do about the rats? Sometimes I say, well, first let's hold up a mirror, okay? Let's see how you live. Let's see how you waste. Let's see what you eat. Let's be responsible to your yard and everything around you... let's do this intelligently with thinking and not saying, let me go buy some poison at the store.
Wartha: So welcome to the backyard of the building
Charli: Oh yeah, so it's pretty open. I'm spotting some bins.
Back at my friend’s apartment building, where we started this episode, we’ve emerged from the basement and its stifling odour to check out her bin situation.
Wartha: These are the bins over here.
Charli: Yeah, okay. All right, so we're approaching some giant tubs, giant bins and they're completely overflowing with rubbish, the lids aren't secured, they're not tight because... there's bags of rubbish flowing out of them. Not to shame you on international radio...
Wartha: Yeah, I mean there is food waste next to the bins and the tenants usually don't throw the bags inside the bins but if they are crammed next to the bins.
Suffice to say, it didn’t take much Sherlock Holmes-ing to guess what the rats might be feeding on.
Charli: Who shares these?
Wartha: All these apartments and the next building.
Charli: That’s heaps.
Wartha: Yeah it’s not enough bins for tenants.
Out the back of her building, there were two bins being shared among 20 apartments. Next to the bins was a big grassy area with trees and shrubs – perfect for brown rat burrows.
Charli: So yeah, every bin is open and there is trash flowing out of it. You can see food and stuff like that. And those bags are open, so maybe, yeah, there's holes in them actually. Is that... a rat hole?
Bobby: So, you know, it's about food. And I've been teaching for over 40 years. When people say, what to do about the rats in our area? I'm like, no food equals no rats. Pretty simple. But yet we can't seem to get that down for some people. And that's the ones the rats take advantage of.
Overflowing, easy-access bins full of food scraps and dirty containers – this is prime rat fodder. Not to mention the food discarded on the roadside and flushed down the toilet – adding to the rat-sewerage problem.
Food waste in and of itself is an enormous climate issue. It contributes around 10% of global greenhouse gas emissions – so around five times that of flying.
To be clear, Wartha tries her best to manage her own food waste cleanly and responsibly, she puts it in a bag in the bin and closes the lid, but, when there’s too much waste for the available bins, it’s an uphill battle.
Even if we try to reduce much food waste as possible... at the end of the day, people are going to throw at least some food and food-contaminated packaging away. So, how can you best deal with it to avoid making it a little rat paradise?
Bobby: You need to keep cans, for example, clean. need, you know, people put their bags in it, weeks go by and they never think about cleaning the garbage can. If they don't, all those molecules of old grease and old stains and particles that we can't even think of or see, you know, they're wafting along the bottom of that ground in currents.
Bobby says this is where it’s important to pay attention to the kind of outdoor trash can you have – does it have a secure lid, is it intact? If it’s provided by the city, does it need replacing?
By the way, there’s this one common misconception that compost is particularly attractive to rats. But he says that’s not true. Because, if they can choose, their preference isn’t moldy, decomposing food covered in dirt.
Bobby: They want their food to be fresh as can be, and they want it dependable, and they want it to be tasty, exactly as we are as mammals... So composting is not a rat attractant by any means whatsoever.
And beyond individuals throwing stuff in the bin, it’s a collective effort.
Bobby: The city itself must play an important role. They cannot just leave litter baskets full all night long until the morning because if they do, they're growing rats for that particular block of that city.
So, as a highly experienced rat tamer... what does Bobby’s household bin situation look like?
Bobby: We use good containers that have good lids that lock down. We keep our trash very clean within those containers. We clean the containers themselves. We don't leave them in areas where food molecules are attracting not just rats, but raccoons and squirrels and... you know, any other animal that's just simply looking for a meal.
They’re not perfect, he says, but they don’t see rats...
Bobby: You know, we probably over-consume food. So there's times when I know I'm like, gee, I wish I...Thought about that a little clearer because now I have more waste and I feel a little bit guilty. So I try and we try as a couple, my wife and I, to be very cognizant of not wasting food... Do we ever see rats? We don't, but I know they're in our area. I hear people complaining, it's like, well, we saw some rats across town over here...
There is another, tricky thing that does tend to play a big role in whether or not people are willing to try the preventative method. And it’s something that’s hard to introduce where it doesn’t already grow organically.
Bobby: I use that word very carefully, it has to be a culture. It has to be a town or city where everybody that grew up in that city learns early on as children, this is the way you do households... And it's in some ways should be somewhat of a minor sin, if you will, to walk down the street and drop litter and just walk away from that and or throw it or not do your trash correctly. That’s a sin on a community.
And the thing about big, dense metropolitan cities like New York and Berlin is that they tend to comprise a lot of different people with many different values and attitudes.
Bobby: People always ask me, well, there's a rat-free Providence in Canada, and how do they do it, you know, versus New York City? I'm like, we can't make such comparisons because one city has 10 to 12 million people in a very, very small area, and it's difficult to manage such densities in a practical scale...
The Providence of Canada, rat-free, you know, it's very low density. And low density means low amounts of garbage, and low amounts of garbage means very few rats can make a living. So, it's not as simple as, you know, why don't we do what a clean city does? It's very complex. You have to sit down with all the leaders of the cities who do it right and with the ones who are still struggling, and say, what can you do?
The thing is, whether we like it or not: rats live here, too. Just like us, they’re trying their best to survive. And it just so happens, many of the cities we’ve built – full of free-to-access food, warmth and shelter – they really quite like it.
Bobby: As we develop cities, we displace all the animals in that area. For example, we put in a new subdivision of houses that carries over to 100 acres or 200 acres. Well, there were wild animals living in those areas in balance. And now we've completely wiped out that environment and it no longer exists. And everybody in that environment, the birds, the small mammals, the reptiles, the insects, everything in there, has now been, quote, kicked out. And too bad, so sad, see you, get out of our way. And these animals that can move about, that have been kicked out of their natural environment, and rats, by the way, can live in natural environments, they're like, what do we do? And they circle back around, well, here's a brand new hollow tree that just went up and this hollow tree spills garbage every night. I might as well move close.
You don’t have to love rats – or even like them – to learn to better coexist with them and keep them out of your stuff. But, Bobby says, rats probably deserve a bit more respect than we give them. I personally quite like rats now, even despite the smell in my friend’s basement. But of course. I don’t want them in my stuff. And based on Bobby’s advice, if we want fewer rats in our homes, our basements and our streets, we’re going to have to take a harder look at what’s attracting them there in the first place.
Bobby: We have this you know, attitude of arrogance. Like, you know, we can do anything we want to these rats because they're in our space. Instead of saying, why did you call them to your space? Why did you attract them to your space? They're only looking for food and a place to hide.
Because, in the end, as long as cities keep producing an endless supply of food scraps, and the cracks to access it, rats will keep finding a way in.
*phone ringing*
Wartha: Hi Charli...
Charli: Hi Wartha! ...I just wanted an update on the situation... like, where are you at now? What are you going to do now, anything different?
Wartha: I mean, me as an individual... I don’t think I can do much. I’m already separating waste, I’m not flushing food down the toilet or in the sink, and I’ve asked my landlord to provide more bins but they are not responding and that’s a whole other issue but a lot of landlords are not taking care of their buildings or the tenants sufficiently, and that has an impact on the rat problem in the city.
Charli: Has anything we’ve spoken about recently changed the way you think about rats or how you approach this?
Wartha: Haha. They are quite cute animals I guess, generally speaking, but, if they’re infesting your building, I’m not able to generate warmer feelings towards them. So, no, I don’t feel much more differently towards rats in the city or in particular in my building. But yeah, it’s the human that is the problem, not the rat I would say.
Charli: Thank you so much for coming on this little rat journey with me.
Wartha: I’m sorry you had to experience it.
Charli: I think it brought us closer together.
Wartha: I think so, too.
This episode was written and produced by me, Charli Shield. It was edited by Neil King. I did the soundscaping and final mix. Our sound engineers were Gerd Georgii and Jürgen Kuhn. What did you think of this episode? You can send us your feedback in email form to livingplanet@dw.com, or leave your comments for us on Spotify, on Apple Podcasts, or on YouTube. If you want to send us a voice message – with feedback, an idea or a question, go to speakpipe.com/livingplanet and press record. It’s easy, it’s fun, and, who knows, you might hear yourself on the show one day... Living Planet is produced by DW Studios in Germany. Thank you so much for listening.
This episode was created with the help of Zapsplat sound effects.