ibyen
This is the Copenhagen resident you really don't want to encounter
But they're having a great time in our parks
They're feasting their way through the city's food scene
And even though we fight them, they've already won long ago
Have we completely misunderstood the urban rat?
It is early spring at my allotment house in Sydhavn. I am here to clean out all the rat nests that have grown large in the house over the winter.
The rats have sought shelter from the rain. They have dug into the rock wool, which now lies in small fluffy tufts on the floor. In the corners, an unknown number of hairy beasts have gathered capsules, snail shells, mussel shells, plastic packaging, stones.
Wearing rubber gloves and with a determined look, my parents and I have filled buckets with collected rat treasures, and with sweaty brows, we sit down at the lunch table.
»Can a rat smile?« I ask.
The night before, I had noted the question on my phone, just minutes before falling asleep. I had rats on my mind.
My father answers immediately.
»If you look closely, the rat actually has an incredibly friendly face.«
Over the past year, I have really struggled with these small rodents. Periodically, I have had to check each evening if there was a rat in the trap in my allotment house.
I have been in close contact with so many dead rats that I have stopped counting.
Through the streets of Copenhagen, I have cycled with them in black garbage bags, searching for a trash can because the allotments are closed for the winter. The rats have dangled lifelessly against my pants leg, and the only thing shielding me from their greasy fur has been a 30-micron plastic bag.
The brown rats live side by side with us. They live under our awnings, scurry around in our courtyards, gnaw tunnels under our floorboards.
The relationship between humans and rats is commensal. Commensalism occurs when two species live together, but only one benefits from it. The term comes from the Latin commensalis, meaning ’to eat at the same table’.
And indeed, we humans do. We eat at the same table as the rats.
At the same time, the topic of ’rats’ evokes anecdotes. There was the rat at Landemærket, which haunted Kongens Have and with its length of 58.5 cm created terror. Or the restaurateur on Danasvej in Frederiksberg who had to close his spaghetti restaurant after seven weeks because the rodents had gobbled through the wooden floor in two days. Not to mention the baby in a pram who was bitten by a rat in Østerbro.
But rats also carry another truth, besides being gross.
Whether we like it or not, the number of rats seems to be increasing. We will never get rid of them. And they will continue to scurry across Enghave Plads in the evening sun, now and in the future. So in this article, I will try to make eye contact with the nasty rats.
In cities like Amsterdam and Paris, people are already beginning to change their perception of them. Or they are returning to a previous view of rats. One from the last century.
Paradise for Rattus
There are two cute pandas at the Copenhagen Zoo, who eat bamboo and stare into space. They do not mate. Despite the zookeepers’ grand plans over the past six years to bring new offspring into the world, it still hasn’t happened. This year, the zookeepers released a press statement titled: ’Annual panda mating: Here is the strategy:’
»Only when she ’stands correctly’ – that is, with an arched back, completely still, and with her tail up – will we put them together,« the meticulous planning states.
But it did not work this year either. In April, the zookeepers announced that they had once again given up on the mating. There is a window of 12 to 36 hours in the spring when the panda is willing to think about sex. The rest of the year, there is no interest, not even a little.
And here’s the thing about rats. They just get to it. Quickly and efficiently. One male, one female, and soon there are baby rats. That’s one of the reasons why rats are so hard for humans to control.
A rat pair can multiply into 862 rats within a year. A rat’s life is harsh. There is a huge mortality rate. They drown, are killed by predators, rat hunters, and poison. But due to their ability to reproduce, the numbers still grow.
They are the animal in the world that has adapted best to the human-made world. As long as humans exist, rats will live.
While the panda needs an intensive protection program in the wild to survive, we are looking at a future where the number of humans and rats will increase, almost in sync with each other.
A report from Science Advances in January analyzed rat populations in 16 major cities, and researchers concluded that the rat population has increased in 11 out of 16 cities, particularly in Washington, D.C., San Francisco, Toronto, New York, and Amsterdam.
It’s one of the largest global data-driven research projects on urban rat populations. The study has several thought-provoking conclusions about rat numbers:
First, there are more rats, the higher the population density in the cities. Additionally, urban areas with the least vegetation have a higher number of rats. That is, the more buildings and people, the more rats.
And then there is the report’s most remarkable finding, which made headlines around the world:
The researchers showed that in cities where temperatures rise faster, the number increases the most. When the planet gets warmer, rats get better conditions.
The researchers believe it is because the rat gets more months per year to utilize its incredible ability to reproduce.
The finding has led politicians in Toronto, who really struggle with rats, to call the current situation the »perfect rat storm«. The bottom line is that the world we humans have created is a paradise for animals of the genus Rattus.
In Copenhagen, the cost of rat control has increased by 57 percent from DKK 11.3 million to DKK 17.4 million from 2013 to 2024. However, no one knows the number of rats in the city. It is incredibly difficult to calculate how many live in the underworld of sewer pipes.
.»In Copenhagen, the cost of rat control has increased by 57 percent from DKK 11.3 million to DKK 17.4 million from 2013 to 2024«
By ship from Russia
Other pests also belong to urban life: scabies, bedbugs, silverfish. But the rat is considered by many to be the most disgusting. This is something that specialist veterinarian and researcher at Aarhus University Aage Olsen Alstrup can wholeheartedly agree with.
He is responsible for pest control at his department of the university. In other words, he has handled a great number of laboratory rats over the past 26 years.
»When people hear that I work with rats, some of them simply exclaim: Yuck!« he says when I call him to learn more about the lifestyle of rats.
»Rats are simply the worst thing you can encounter in your home or garden.«
Even at the university, he experiences skepticism among participants in laboratory animal courses, who find the lab rats repulsive.
»It’s ingrained in our culture that the rat has been a pest. That it has destroyed houses and food supplies over hundreds of years, making the sight of a rat catastrophic.«
In the same way that seeing a snake or spider triggers a primal instinct in us, seeing a rat does too. It’s not rational to be afraid of a rat; it will never run over and bite a human. However, the presence of a rat reminds us of danger: it is a pest, and it always has been, says Aage Olsen Alstrup.
The most common rat in Denmark is the brown rat. It arrived here from India in the 18th century by ship via Russia. Over time, it has almost completely outcompeted the black rat, which was the species that spread the plague in 17th-century Europe.
None of this was known before a couple of French researchers in the 1890s proved that the plague was carried by fleas in rats’ fur. In the Middle Ages, the rat was actually seen as a sign of health.
In modern times, however, Aage Olsen Alstrup cannot recall the rat ever being depicted as a positive symbol.
And yet...
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Rats have an excellent sense of smell, are skilled diggers, and are strong swimmers. A rat is incredibly strong and can lift a grate weighing up to 1.2 kg. Their teeth grow continuously, about 14 cm per year. Thanks to their muscular hind legs, they can jump 1 meter and climb walls. They are also agile and can squeeze through a hole as small as 2 cm.
Psychologically, rats are fascinating. They live in groups with multiple generations and help each other. Rats scream when something hurts or is uncomfortable, and the rest of the group responds. When encountering something new, only one rat from the group will go forward until the others see that it is safe. Rats form lifelong bonds with each other.
Studies also show that rats have a certain degree of imagination and cognitive abilities. They can navigate through an area they’ve previously explored using their thoughts alone.
Rats have a good memory and can recall what they’ve eaten in the last 8 hours, allowing them to connect stomach pain with the decision not to eat more rat poison.
They help each other even without any personal gain, and if they receive a reward, they share it with others.
Source: Specialist Veterinarian Aage Olsen Alstrup, Institute of Clinical Medicine, Aarhus University
In the specialist veterinarian’s »little world of researchers«, there exists a different and much more positive view of the rat. It is seen as fascinating and impressive with its »biological super body«.
It is intelligent with many talents, he says:
»The rat is just a very small human.«
Rodents with diarrhea
The fact that the rat is here to stay is the entire premise of the research center Helsinki Urban Rat Project, founded in 2018.
Their research examines, among other things, the distribution of rat populations in the city, urban rat parasites, and not least the interaction between humans and rats.
The Urban Rat Project works with the hope of a future where we have a less gruesome relationship with rats. A relationship built on greater knowledge rather than perceptions. Surprisingly little has been studied about urban rats, even though we have all sorts of ideas about them.
Tuomas Aivelo explains all this over a video connection. He is the head of the Urban Rat Project and conducts several of their research projects. At the end of June, he will give a presentation at an international conference on urban pests at the University of Lund titled ‘Why Do We Kill Rats?’.
So... why do we kill rats?
There’s a brief silence over the video call as Tuomas Aivelo carefully chooses his words.
»Yes... We... yes, I actually don’t have an answer to that.«
BEHIND THE PHOTOS
How should we illustrate a story about Copenhagen’s rats? We asked ourselves at the Ibyen editorial team. So, we invited two live feeder rats from Tårnby Minizoo to the journalist’s apartment.
Because if a rat is »just a very small human,« as an expert says, then the city rat must be a small Copenhagener, eating shared dishes, picnicking in Frederiksberg Gardens, and hanging out with its knitting at Assistens Cemetery.
The dollhouse furniture was gathered with the help of a grandfather, an editor, and a basement in Valby.
Even though Tuomas Aivelo has initiated 11 research projects over the past seven years on rat control and human-rat relations, he still cannot answer why exactly we kill them, aside from the obvious aspect of human nature: »We say ’Shoot!’ when we see a dangerous animal.«
In Tuomas Aivelo’s eyes, much of the world’s rat control is not very evidence-based.
For instance, Finnish legislation states that every homeowner has the right to kill rats because they pose a health risk. But there is just one problem, Tuomas Aivelo points out.
»Historically, we’ve seen very little evidence that diseases are actually transmitted from rats to humans.«
»I would say – and I feel confident in saying this – that it is very rare for people in Helsinki to actually get sick from rats.«
This is because humans very rarely come into direct contact with rats – or their feces for that matter. The institute, for example, has investigated this:
15 percent of all rats in Helsinki carry campylobacter bacteria, which cause a week of diarrhea. It can therefore infect humans if they come into contact with rat feces. But how would one do that? The chance is actually quite small, Tuomas Aivelo points out.
»But what if we turn the question around: How do rats actually get infected with campylobacter?«
»We have calculated that around the clock in Helsinki, there will be at least one person with diarrhea who is emptying themselves into the sewer system. So there is a greater likelihood that humans are infecting the rats, rather than the other way around.«
So instead of asking how we avoid getting infected by rats, it should be more about how we avoid infecting rats with our diarrhea or other diseases. Or as Tuomas Aivelo says:
»We get a healthier city when we have healthy rats.«
The price of a dead rat
Before 1945, people handled rat control themselves. That means every homeowner did a bit of rat control to the best of their ability.
But after World War II, modern rat poison was developed, and it changed our relationship with the rodent. Until then, we had lived with them because it was impossible to kill them all, says Tuomas Aivelo.
But along with rat poison came companies’ promises to eradicate all rats in the city. This created a shift in how we perceived the furry city dweller:
Now it could actually be eradicated. So we tried.
Throughout the 50s, 60s, and 70s, more resources were allocated to the fight, and it became systematized in companies that handled pest control.
Initially, the argument was to prevent building damage, and in the 60s and 70s, arguments about disease transmission also emerged, says Tuomas Aivelo.
.»In recent years, there has been a shift in the perception of rats in other European cities«
Today, many people believe that rats must be eradicated, and we must kill them to get rid of them. Even though scientists pointed out as early as the 1950s that it is impossible to eliminate all rats, the idea persisted.
Many city dwellers still view the rat as a species that must be combated with poison and killed. It is not seen as a natural part of the city.
Rats, however, are very good at learning from each other, so they avoid rat poison. Additionally, they become resistant over time. So, in reality, we cannot eradicate them. And the spread of rat poison also has consequences for the entire ecosystem.
In Finland, 82 percent of all predators have traces of rat poison in them. Rat poison also annually kills both cats and dogs, says Tuomas Aivelo.
»So the question is: How many cats and dogs can we let die each year?«
»And what would the calculation look like if it also killed a baby? How many children would we then allow to die?«
A new perspective on rats?
About once a week, Tuomas Aivelo is called by a journalist who wants to know how many rats are in Helsinki. And the answer is: No one knows.
»I usually say anywhere between 10,000 and 100,000, but it’s all guesswork.«
»Barcelona is one of the European capital cities that has invested massively in mapping the number of rats in the sewers, and the number is around 259,000,« he points out.
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No one knows the exact number of rats living in Copenhagen. Each year, the municipality receives around 7,000-8,000 citizen reports about rats. This number has remained stable, with a slight increase in recent years. In the late ’90s, reports were around 3,500-4,000 annually. It’s unclear whether we’re simply better at reporting sightings or if the rat population has increased.
In Stockholm, Aftenposten estimates around 2.8 million rats. In Paris, the municipality estimated 4 million rats in 2016. In London, there could be up to 9 million, according to The Telegraph.
We’re in the dark. No one really knows. Barcelona was one of the first cities to conduct a municipal rat count using cameras in 2018. The report concluded there were 259,000 rats in the city—one for every six residents.
A common factor for all cities is that rats and pests are a growing problem, regardless of their numbers.
Source: Technical and Environmental Administration, Copenhagen Municipality
So when Aftonposten writes that there are 2.8 million rats in Stockholm, the number sounds exaggerated to the researcher. But regardless of the number, the motto in all the world’s major cities is that the rat must die. And here we return to the question of why they must die.
Maybe the answer is actually quite simple, says Tuomas Aivelo.
»We kill rats because they are in our trash cans.«
There are certain places where animals can live that are ’correct’ – and some that are ’incorrect.’ In a world where animals are created in our image, rats do not fit in.
In recent years, however, there has been a shift in the perception of rats in other European cities.
In Amsterdam, politicians are working to return to the idea of the rat as a cohabitant and have therefore funded the research project ‘City Rat Project.’
Here, researchers are investigating how closely humans and rats can live together. They are suggesting, among other things, creating a natural habitat for the rats in Amsterdam, where the city’s residents can get closer to them.
In 2023, Paris’ mayor established a special working group that also investigates the potential for coexistence: Projet Armaguedon – Project Armageddon. The goal is to create better knowledge about health risks – real and perceived – and more importantly, to find the best way to make rats our allies, writes the French newspaper Le Monde about the project, which is still in its exploratory phase.
»Does the presence of brown rats in Paris pose a real public health risk?« asked Anne Souyris, deputy mayor responsible for public health, in a post on X, ending the post:
»We need scientific advice – not political judgments.«
The reaction came after several right-wing politicians criticized the project’s unconventional approach to rats.
Like dandelions
In Copenhagen, there is no indication that we are changing our attitude toward rats. At the pest control in Copenhagen’s technical and environmental administration, the answer is that the rat is an animal that »must be controlled.«
»You won’t get me to say that we should make room for the rat,« says environmental coordinator Michael Møller.
»Not here in Copenhagen. Certainly not in Denmark. You won’t get any municipalities to go along with that.«
So, it will be a no to rat coexistence in the capital. At least if you ask the municipality – and this contrasts with what researcher Tuomas Aivelo in Helsinki would like to see happen.
He believes we need to start thinking differently:
»We need to listen to what the rats are telling us. And yes, live alongside them – in some way.«
When we talk about increased biodiversity in the city, it also contributes to increasing the number of rat lives, even though we might prefer to think about the good things with more green areas.
Rat control starts with ourselves: It’s about how we design the city and our habits – when we feed birds, pour oatmeal down the drain, or overfill trash cans.
»Rat control is human control,« he says with a one-liner that could be printed on a T-shirt.
In all human worlds, there are rats, and we must share Enghave Plads with them.
They are like dandelions breaking through the asphalt.
Or just like humans, spreading across the world for their own sake.
Editorial staff
Text: Søren Korsholm
Photo: Nicolai West
Video: Lærke Berg-Pedersen
Editing: Louise Skov Andersen
Digital coordination: Rasmus Vendrup
Editor: Morten Hjortshøj