We’ve built a world for rats #LivingPlanet

0:04 DW Living Planet I'm actually quite scared to go down.

0:19 Oh my god.

0:21 Do you smell it?

0:22 I'm really scared.

0:23 Yeah.

0:23 Yeah, it's stinky.

0:25 Deep in the basement of an apartment building

0:27 in Berlin South lingers a stench that's hard to forget.

0:34 Okay.

0:34 Oh.

0:36 This is my basement.

0:38 Or our communal basement.

0:41 You can come in.

0:44 It's quite intoxicating.

0:45 [music] The scent is heavy, pungent, asphyxiating.

0:50 can see poop quite a lot.

0:53 Coupled with small, dark droppings, a slick, black, greasy slime,

0:57 and small, jagged holes, it can only mean one thing.

1:01 I feel like I can't breathe properly.

1:03 Rats.

1:14 Los Angeles is dealing with an unwelcome title.

1:21 Rats are moving in.

1:23 Dude, the rats in New York City have just Oh, yeah.

1:25 I seen George neighborhood experiencing rat infestation.

1:29 Imagine the terror of rats being in every wall and every ceiling of your home.

1:36 Despite centuries of our dogged efforts to get rid of them,

1:39 rats still live among us.

1:42 Sometimes awfully close.

1:44 Not only that, in many cities, they are multiplying.

1:48 From Berlin to New York to Toronto,

1:50 it appears rats aren't just surviving, they are thriving.

1:54 It's been named the city with the biggest rat problem in America.

1:58 They're called roof rats, and there's hundreds of them here.

2:02 Rats are chewing their way into homes looking for water and nesting materials.

2:06 Millions of them underground.

2:07 They they live in these little Oh, yeah.

2:09 tunnels and and they just feed off our garbage.

2:13 So, what is going on?

2:15 Are rats taking over?

2:17 Or are they showing us something about the way we live?

2:21 I'm Charlie Shield.

2:22 Today on Living Planet, what urban rats can teach us about our cities,

2:27 our habits, and the systems that keep them coming back.

2:30 [music] I see them sometimes if I go out to throw away trash.

2:41 They run around here, and you can hear like scratching within the bins,

2:45 and then there are like opened up, ripped up bags.

2:48 We're starting this episode in Neukölln, a suburb in the south of Berlin.

2:53 Where my friend Varta rents a flat on the third

2:56 floor of an apartment building built in the 1940s.

3:00 And where colony of rats appears to have moved into her basement.

3:04 As you can see, these windows lead to the basement.

3:08 The lower windows?

3:10 Yeah.

3:10 And I assume that the rats can just access the basement through these windows,

3:15 and maybe they actually live here.

3:17 Varta hasn't actually been down to her basement for 9 months.

3:21 The last time she was here, she got a fright.

3:24 One rat actually crossed my foot.

3:27 Like ran over my foot.

3:29 She has sought help to get rid of them.

3:31 The pest controller came by, and he said that that not only our street,

3:35 but also the other streets have a rat problem,

3:38 and that it doesn't really make sense to put in rat traps,

3:42 that they would eat whatever is out there instead of what

3:47 is like put in the rat traps to kill them.

3:51 And that there's also a problem with the sewage system.

3:55 There is like leakage in the sewage system.

3:59 Varta's predicament is not unique in Berlin.

4:02 About 3 and 1/2 million people live in Germany's capital.

4:07 Alongside them, in a great many nooks and crannies,

4:09 burrows, buildings, drains, and sewers, live many, many rats.

4:15 They scuttle along the tracks in the underground.

4:17 They dart in and out of the bushes at the park.

4:19 And they inhabit the trash cans and the plastic bags discarded on the curb.

4:24 It's almost impossible to estimate just how many rats live in any one city.

4:29 They're nocturnal, and they breed like mad.

4:33 Estimates for Berlin range from hundreds of thousands to [music] millions.

4:38 And this got me wondering, what exactly is fueling the [music] rat problem?

4:43 And could there be a better way to manage human-rat relations?

4:47 Or is this it?

4:49 To find out, I needed to look beyond this basement and beyond Berlin.

4:56 Okay, we're recording over here.

5:00 My heart was pounding.

5:01 I was nervous.

5:02 I was scared.

5:03 I didn't know what was about to happen.

5:05 You know, will they attack me?

5:07 Will they bite me?

5:08 Will they reject me?

5:10 When you start researching rats in cities,

5:13 it only takes a couple of clicks before you

5:15 see this one guy's name pop up again and again.

5:18 Bobby Corrigan?

5:20 Bobby Corrigan.

5:21 Literally, I moved in.

5:23 I brought my camping gear.

5:25 I brought my sleeping bags, my food.

5:27 Bobby is an urban rodentologist.

5:30 That's a scientist that studies city rats and mice.

5:34 A job he's had for 43 years.

5:37 And as you can hear, he's taken it seriously from day dot.

5:40 And I lived with the rats that when they were asleep, I was asleep.

5:44 And when they were up, I was up making all kinds of observations.

5:48 Bobby is talking about living with rats in barns in Indiana,

5:52 outside Purdue University, where he studied.

5:56 Back when he first started studying rodents,

5:58 which he came to do almost by complete accident, he told me.

6:02 Bobby cohabited with rat colonies in these barns for weeks on end,

6:07 trying to get to know them.

6:09 And although when he first moved in, he was petrified,

6:12 once both the rats and Bobby's nerves were settled, they got on quite well.

6:17 Nothing happened other than I was able to watch them.

6:20 They looked completely uh skittish of me was the best term.

6:24 They would they would approach, they'd run away, they'd squeak,

6:27 they'd approach closer the next time and run away.

6:31 Gradually, Bobby faded into the background.

6:34 Pretty soon, you know, they accepted me is the term I'll use.

6:38 I don't know if they ever did or not,

6:40 but they certainly um weren't aggressive towards me,

6:43 and they weren't afraid of me.

6:45 So, after a while, I was able to feed them by hand.

6:47 They would come closer and closer.

6:50 And pretty much the colony seemed to um I you know, become normalized.

6:55 They they seemed to like, "Okay, we have a new guy here,

6:58 this guy Bobby, that's hanging out with us.

7:00 He's not doing us any harm." And I started taking notes.

7:04 After a while, they tend to ignore me.

7:07 And I watched them interact with each other.

7:10 He watched rats groom each other, play, wrestle,

7:13 and deliver food to other sick or elderly rats.

7:16 I saw rats um being kind, and that's the best word.

7:20 At the same time, he also watched

7:22 bully rats attack others for no apparent reason.

7:25 Just like we see with people.

7:27 I'm like, "Was I imagining that?

7:29 Was that real?

7:30 You know, has this been published?

7:32 Has anyone studying these things?" And some

7:35 of those behaviors um weren't published at the time.

7:38 But now, they have been in good journals, refereed science journals.

7:43 And you know, we do know that rats

7:46 have the same emotional drives as human beings do.

7:50 Happiness, sadness, depression, caution, you know, all of that.

7:56 Often, Bobby had the feeling he was watching

7:58 a very human colony from above, he said.

8:01 And of course, you know, psychologists would probably say,

8:05 you know, "That's no surprise at all.

8:07 The mammal brain is the mammal brain,

8:09 whether it's whales or humans or bears or rats." Fast forward to now,

8:19 and Bobby has long been teaching rodent boot

8:22 camps and leading rat safaris through New York City.

8:26 I call them rat safaris cuz that's what they are.

8:29 Yes, people want to go on those.

8:31 At night, it's that's their world.

8:32 They are nighttime creatures,

8:34 and usually from dusk till about 2 hours afterwards is your best

8:39 time to have a chance to see rats doing their natural thing.

8:46 I usually take safaris out of Lower Manhattan.

8:50 It's down on the southern end facing the Statue of Liberty.

8:55 The reason for that choice is it's among

8:58 the oldest portions of [music] New York City.

9:01 And what that means is the sewers are very old.

9:05 And there's probably channels below that city that we don't even know about.

9:10 Channels that we don't know about,

9:12 but the rats who live in New York City certainly do.

9:16 [music] And the interesting thing there is the rats,

9:18 they they were deposited onto US shores through European ships,

9:23 as best as we know, probably in the early 1700s.

9:27 And they started establishing tunnels and pathways all

9:31 the way back then that to this day, some of them still exist.

9:37 The rat species that rocked up with the European colonizers was the brown rat,

9:42 which originated in current-day Mongolia and northern China.

9:46 It's the most common species today, [music]

9:48 the one you're most likely to find rifling

9:50 through your trash or scurrying about in the bushes.

9:53 The second most common is the smaller, sleeker black rat,

9:57 which has been traced back to Southeast Asia.

10:00 And these urban rat species are just

10:02 about the most successful species on the planet,

10:05 having established themselves [music] on every continent bar Antarctica.

10:09 And over thousands of years, you know,

10:12 traveled about and you know, with humankind,

10:15 they started getting on their wagons as they

10:18 started traveling about and pretty soon the Silk

10:21 Road and avenues westward and ships and the rest

10:25 is history as we started developing transportation,

10:29 they ended up the globe over.

10:35 [music] [music] Part of why urban rat species have been so successful

10:45 is because they figured out how to live alongside humans,

10:49 Earth's other dominant species, very successfully.

10:53 They're called commensal rodents in the literature,

10:56 which means to share the table.

10:58 Now, we don't do that willingly,

11:01 but we use that term because through eons of time,

11:05 they're constantly getting to our food that we want to eat and share it.

11:09 So, but they're competing with us in that regard.

11:12 And the other word that's kind of cool is a word called kleptoparasitic.

11:17 We all know what parasites are and kleptoparasites, right?

11:21 So, a kleptomaniac is someone that constantly steals things.

11:28 [music] Well, the rats are kleptoparasitic on us.

11:30 They're always stealing our food.

11:34 Rats have always been incredible breeders.

11:38 [music] Under ideal conditions,

11:38 one pair of rats can produce 1,000 offspring within [music] a year.

11:44 And those ideal conditions are often in cities,

11:48 where there are more and more humans with which

11:50 to share the table and steal from, especially nowadays.

11:54 Well, here in the lower mainland, that means rat problems are on the rise.

11:58 Rats have taken over the neighborhood,

12:00 living in the walls and dining on insulation.

12:03 CTV's Austin joins us live.

12:06 In early 2025, Bobby and a global team

12:08 of colleagues published a paper in Science Advances showing

12:12 urban rat numbers were on the up in major

12:14 cities from New York to Washington to Amsterdam.

12:18 They found that as cities are expanding

12:20 over larger areas and human population density increases,

12:25 rat populations are increasing, too.

12:27 And so, it's about food, it's about urbanization, and it's about people density.

12:33 As we increase our ways, the rats are going to benefit from that.

12:38 And they found something else as well.

12:40 A link between cities getting hotter

12:42 from climate change and rapidly rising rat populations.

12:47 They think that's because shorter winters

12:49 mean longer breeding seasons for rats, who,

12:52 as we've covered, can get a lot done in a short space of time.

12:57 And there tends to be more food available during the warmer months.

13:00 And so, when you multiply that by millions of small mammals like rodents,

13:05 you end up with, of course,

13:08 this incredible algorithmic growth in an area where the world over,

13:14 as a consultant, I can tell you I get calls saying,

13:16 "Can you come to our city because we

13:19 are seeing rats like we've never seen before."

13:21 And that's been a gradual thing that caught us

13:25 by surprise over the past decade of a slow,

13:29 slow simmer leading to, like we know, eventually a boil over.

13:34 And that's what's going on.

13:37 In many ways, rats are loving this brave

13:40 new world that we've engineered for them.

13:50 But, apart from being universally disliked,

13:53 what threats do rats actually pose to humans?

13:57 Well, they can carry diseases like leptospirosis,

14:01 hantavirus pulmonary syndrome, and the bubonic plague.

14:05 They also like to chew through electrical wiring because,

14:08 Bobby says, to them it just looks like a plant.

14:12 And they can cause infrastructure damage, destroy our belongings,

14:15 and invade and contaminate food manufacturing, storage, and processing.

14:21 Research has also shown that people living

14:23 with rat infestations [music] have poorer mental health.

14:30 So, though Bobby doesn't think the vitriol thrown

14:32 at rats in our culture is really justified,

14:35 he does argue that for public health and safety,

14:38 we do need to keep a healthy distance.

14:40 People feel like they can do anything to kill a rat and it's okay,

14:45 but in my opinion, it's not okay.

14:47 It's another mammal, but nevertheless, we do have to manage them out of our city

14:52 so they don't bring us any disease or germs.

14:56 This brings us to rat management methods and why many of them fall short.

15:02 The most common rat control methods involve lethal poison and traps.

15:07 Back in the 1980s, a rat

15:08 poison called second-generation anticoagulant rodenticide was invented

15:13 after pest controllers realized that rats had

15:16 developed an immunity to the first-generation stuff.

15:18 When getting rid of rats and mice is almost as easy as saying disappear.

15:23 Here's the secret.

15:24 eBay.

15:26 And not to get technical, but they just simply,

15:29 you know, made them more powerful.

15:31 The poison basically works by causing rats to bleed to death.

15:35 Well, it seemed terrific like, well,

15:38 no more resistant rodents to the new generation of poisons.

15:42 Until A controversial poison used to kill

15:45 rats is coming under scrutiny for killing wildlife.

15:48 That's the claim of Well, now, 40 years,

15:51 45 [snorts] years later, we realize that those animals,

15:56 if they're eaten, say by a hawk or an owl or a bobcat or a fox,

16:03 you know, if they are consumed by almost any other carnivore or bird, in turn,

16:11 we're poisoning those animals through secondary toxicity when they

16:17 eat today's current rat poisons if they're the anticoagulants.

16:22 So, here we are in furthering damage to the balance of Earth

16:27 by putting out poisons that we're thinking we're killing only rodents when,

16:32 in fact, we're killing other mammals.

16:35 And in addition to the fact that these can

16:37 be cruel and bad for biodiversity at large,

16:40 centuries of trying have shown us that trapping and poisoning rats is

16:43 just not all that effective

16:45 for controlling their populations while being expensive.

16:49 Cities are still crawling with rats.

16:52 So, what could a more effective and sustainable alternative to poison be?

17:04 Experts like Bobby advocate for prevention rather than poison.

17:08 And that starts with paying attention to something we do every day.

17:12 When people ask me, "What do What do I do about the rats?" Sometimes I say,

17:16 "Well, first, let's hold up a mirror, okay?

17:19 Let's see how you live.

17:20 Let's see how you waste.

17:22 Let's see what you eat.

17:23 Let's be responsible to your yard and everything around you.

17:28 Let's do this intelligently with thinking and not saying,

17:31 'Let me go buy some poison at the store.'" So,

17:37 welcome to the backyard of the building.

17:40 Back at my friend's apartment building in Neukölln in the south of Berlin,

17:43 where we started this episode, we've emerged from the basement and its

17:47 stifling odor to check out her bin situation.

17:50 Are these your bins over here?

17:51 Yep.

17:51 Okay.

17:52 All right.

17:53 So, we're approaching some giant giant

17:56 bins and they're completely overflowing with rubbish.

18:00 The lids aren't secured.

18:01 They're not tied because um there's bags of rubbish flowing out of them.

18:06 Not to shame you on international radio, but Yeah, I mean,

18:10 there is food waste next to the bins and uh

18:14 the tenants usually don't throw the bags inside the bins,

18:18 but if they are cramped next to the bins.

18:22 Suffice to say, it didn't take much Sherlock Holmesing

18:25 to guess what the rats might be feeding on.

18:28 But, who shares these bins?

18:29 All the tenants in this building and in the next two buildings.

18:33 That's heaps.

18:34 Yeah, it's uh not enough bins for tenants.

18:38 Yeah.

18:39 At the back of her building,

18:40 there were two large bins being shared among 20 apartments.

18:45 Next to the bins was a big grassy area with trees and shrubs,

18:48 perfect for brown rat burrows.

18:51 So, yeah, every bin is open and there is trash flowing out of it.

18:57 You can see food and stuff like that.

18:58 And those bags are open.

19:00 Yeah, there's holes in them, actually.

19:04 Is that a rat hole?

19:07 So, you know, it's about food and I've been teaching for over 40 years.

19:13 When people say, "What do we do about the rats in our area?" I'm like,

19:17 "No food equals no rats." Pretty simple,

19:21 but yet we can't seem to get that down for some people,

19:25 and that's the ones the rats take advantage of.

19:27 Overflowing, easy-access bins full of food scraps and dirty containers,

19:32 this is prime rat fodder.

19:35 Not to mention the food discarded on the roadside and flushed down the toilet,

19:39 adding to the rat sewage problem.

19:41 To be clear, Varta tries her best

19:43 to manage her own food waste cleanly and responsibly.

19:47 She puts it in a bag in the bin and closes the lid.

19:50 But when there's too much waste for the available bins, it is an uphill battle.

19:58 Food waste in and of itself is an enormous climate issue.

20:02 It contributes around 10% to annual global greenhouse gas emissions.

20:06 So, around five times aviation emissions.

20:10 But, even if we try to reduce as much food waste as possible,

20:14 at the end of the day, people are going to throw at least some

20:18 food and some food can contaminated packaging away.

20:22 So, how should we best do that to avoid making a little rat paradise?

20:32 [music] You need to keep cans, for example, clean.

20:35 You need, you know, people put their bags in it,

20:38 weeks go by and they never think about cleaning the garbage can.

20:43 If they don't, all those molecules of old grease and old

20:46 stains and particles that we can't even think of see,

20:50 you know, they're wasting along the bottom of that ground in currents.

20:58 [music] Bobby says this is where it's important to pay attention

21:01 to the kind of outdoor trash can that you have.

21:04 Does it have a secure lid?

21:06 Is it intact?

21:08 [music]

21:07 If it's provided by the city, does it need replacing or perhaps duplicating?

21:12 By the way, Bobby says there's this one

21:14 common misconception that compost is particularly attractive to rats.

21:19 But, he says that's not true because if rats can choose,

21:23 their preference isn't moldy, decomposing food covered in dirt.

21:27 They want their food to be fresh as can be

21:30 and they want it dependable and they want it to be tasty.

21:35 Exactly as we are as mammals.

21:37 So, composting is not a a rat attractant by any means whatsoever.

21:42 And beyond individuals throwing stuff in the bin,

21:45 it is a collective effort on the part of cities.

21:49 The city itself must play an important role.

21:52 They cannot just leave litter baskets full all night long until the morning

21:56 because if they do they're growing rats for that particular block of that city.

22:02 So, as a highly experienced rat tamer,

22:05 I asked Bobby what his household bin situation looks like.

22:09 We use good containers that have good lids that lock down.

22:14 We keep our trash very clean within those containers.

22:18 We clean the containers themselves.

22:21 We don't leave them in areas where food molecules are attracting not just rats,

22:26 but raccoons and squirrels and you know,

22:29 any other animal that's just simply looking for a meal.

22:32 So, we do a good They're not perfect, he says, but they don't see rats.

22:36 You know, we we probably over consume food,

22:40 so there's times where and I know I'm like, "Gee,

22:43 I wish I thought about that a little clearer because now

22:45 I have more waste and I feel a little bit guilty,

22:49 you know?" So, I try and we try as a couple, you know,

22:51 my wife and I to be very cognizant of not wasting food.

22:56 Do we ever see rats?

22:58 We don't, but we I know they're in our area.

23:01 I hear people complaining is like, "Well,

23:03 we've saw some rats across town over here."

23:09 There is another tricky thing that does tend

23:11 to play a big role in whether or not

23:13 people are willing to try these preventative methods.

23:17 And it is something that's hard

23:18 to introduce where it doesn't already grow organically.

23:21 There are cities that in particular just the culture of that particular

23:26 town or city and and I use that word very carefully.

23:29 There's it has to be a culture.

23:31 It has to be a town or city where everybody that grew up

23:36 in that city learns early on as children this is the way you do households.

23:43 And it's in some way should be somewhat of a minor sin, if you will,

23:50 to walk down the street and drop litter and just walk away

23:53 from that and or throw it or not do your trash correctly.

23:57 That's a sin on a community.

23:59 And the thing about big, dense,

24:01 metropolitan cities like New York and Berlin is that they're made up

24:05 of a lot of different people with many different values and attitudes.

24:09 People always ask me, "Well,

24:11 there's a rat-free Providence in Canada and how do they do it?" You know,

24:16 versus New York City.

24:19 I'm like, "We can't make such comparisons because one

24:21 city has 10 to 12 million people in a very, very small area and it's difficult

24:29 to manage such densities in a practical scale.

24:33 The Providence of Canada, rat-free, you know, it's it's a very low density.

24:39 And low density means low amounts of garbage and low

24:42 amounts of garbage means very few rats can't make a living.

24:46 So, it's not as simple as, you know, why don't we do what a clean city does?

24:51 It's very complex and that's why I mean you have

24:54 to sit down with all the leaders of these cities

24:57 that do it right and the ones perhaps that are

24:59 still struggling and say "What can you do?" The thing is,

25:12 whether we like it or not, rats live here, too.

25:15 Just like us, they're trying their best to survive.

25:18 And it just so happens that in many

25:20 of the cities we've built full of free to access food, warmth, and shelter,

25:25 [music] they really quite like it.

25:25 As we develop cities, we displace all the animals in that area.

25:31 For example, we put in a new subdivision of houses

25:34 that carries over to 100 acres or 200 acres.

25:40 Well there were wild animals living in those areas in balance.

25:46 And now we've completely wiped out that environment

25:51 and and it no longer exists and everybody in that environment,

25:55 the birds, the small mammals, the reptiles, the insects,

25:59 everything in there now been, quote, kicked out.

26:03 And too bad, so sad, see you, get out of our way.

26:09 [music] And these animals that can move about,

26:11 that have been kicked out of their natural environment,

26:13 and rats, by the way, can live in natural environments they're like,

26:17 "What do we do?" And they circle back around and like,

26:21 "Well here's a brand new hollow tree that just

26:24 went up and this hollow tree spills garbage every night.

26:29 I might as well move close." You don't have to love rats or even like

26:33 them to learn to better coexist with them and keep them out of your stuff.

26:38 But, Bobby says rats probably deserve a bit more respect than we give them.

26:43 I personally quite like rats now,

26:46 even despite the smell in my friend's basement.

26:48 But, of course, I don't want them in my stuff.

26:51 And based on Bobby's advice,

26:53 if we want fewer rats in our homes, our basements, and our streets,

26:57 we're going to have to take a harder look

26:58 at what's attracting them there in the first place.

27:05 Hi, Charlie.

27:07 Hi, Vata.

27:08 I just wanted [clears throat] an update on the situation.

27:12 Where are you at now?

27:13 Are you like, what are you going to do now?

27:16 Anything different?

27:18 I mean, yeah, me as an individual, I don't think I can do much.

27:22 I'm already separating waste.

27:24 I'm not flushing food down the toilet or in the sink and [gasps]

27:30 I've asked the landlord to provide more bins,

27:34 but they are not responding and that's a whole other issue,

27:39 but a lot of landlords yeah,

27:42 are not taking care of their buildings and the tenants sufficiently.

27:47 And that also has an effect on the rat issue in the city.

27:53 Has anything we've talked about recently changed the way you

27:57 think about rats or how you approach this at all?

28:02 They are quite cute animals, generally speaking,

28:07 but if they are infesting your building I'm not

28:11 able to have or generate warmer feelings towards them.

28:17 [laughter] So, no, I I don't feel much more differently

28:22 towards rats in the city or in particular in my building.

28:26 And yeah, it's the human that is the problem, not the rat, I would say.

28:32 Thank you so much for going on this little rat journey with me.

28:38 I'm I'm sorry you had to experience it.

28:41 I think it brought us closer together.

28:43 Yeah, I think so, too.

28:46 [laughter] This episode was written and produced by me, Charlie Shield.

29:00 It was edited by Neil King.

29:02 I did the soundscaping and the final mix

29:04 and our sound engineers were Gad Georgi and Jurgen Kuhl.

29:09 What did you think of this episode?

29:10 You can send us your feedback in [music] email form to livingplanet@dw.com.

29:15 Or you can leave your comments for us on Spotify,

29:18 on Apple Podcasts, or on YouTube.

29:22 We do love reading your comments and your emails,

29:24 but we also really want to hear from you, literally.

29:28 So, if you'd like to send us a voice message with feedback, an idea,

29:31 or a question, go to speakpipe.com/livingplanet

29:33 and just press the big red record button.

29:38 And who knows?

29:40 Maybe you'll hear yourself on the show one day.

29:43 Thank you so much for listening.