In Defence of the Rat
“Rats today are widely seen as filthy, thieving vectors of deadly diseases like plague and hantavirus.”
Text by J. B. MacKinnon
This is an edited version of an article that appeared on September 26, 2023 in Hakai Magazine. Read the original here. The original is available in audio format. Listen now, download, or subscribe to “Hakai Magazine Audio Edition” through your favorite podcast app.
In 1522, “some rats of the diocese” of Autun, France, were charged with criminally eating and destroying barley crops. A skilled legal tactician, one Barthélemy de Chasseneuz, was assigned to defend them.
The case is remembered for its procedural twists and turns. When his clients — guess what? — didn’t show up for their day in court, de Chasseneuz noted that the summons had mentioned only “some rats.” But which ones, specifically? The court ordered that a new summons be addressed to all the rats of Autun. When the rodents still failed to appear, their nimble lawyer had a second defense at the ready. His clients, he said, were widely dispersed, and for them the trip to court amounted to a great journey. The rats needed more time.
Again proceedings were rescheduled, and again the rats missed their date with the law. Of course they did, said de Chasseneuz. To arrive at court, the rats faced the twin perils of vindictive villagers and their bloodthirsty cats; his clients needed guarantees of safe passage. This tested the patience of the villagers’ legal team and, with the two sides unable to settle on a fourth trial date, the court decided in favour of the accused by default. The rats won.
Preposterous? Absolutely. Yet one lesson of de Chasseneuz’s victory is this: if we’re asked to see the world through a rat’s eyes, the results may surprise us. Some 16 human generations (and many more rat generations) later, I find myself pressed to pick up where de Chasseneuz left off.
I do so for two reasons. The first is that the charges against the rat have only grown stronger. Rats today are widely seen as filthy, thieving vectors of deadly diseases like plague and hantavirus. They raid our food supplies, gnaw electrical wires, invade our homes, and undermine critical infrastructure with their burrows. No one knows how much rats cost people worldwide each year, but the total is likely in the hundreds of millions of dollars.
The two most widespread and infamous rat species are the black rat (Rattus rattus) and brown rat (Rattus norvegicus). The former originally came from India, while the latter expanded out of northern China and Mongolia. Aided by our boats, most dramatically in the age of European imperialism, each species transformed into a peculiar kind of marine mammal, one that stows away to reach distant ports. They now inhabit every continent but Antarctica.
As an invasive species, rats are voracious destroyers of wildlife. This is especially true on islands — and they have reached 80 percent of the planet’s island clusters, ranging from the subarctic Faroe Islands in the North Atlantic to several subantarctic isles. Rats have been implicated in nearly one-third of recorded bird, mammal, and reptile extinctions, making them the worst nonhuman invasive species on the planet, followed by cats and mongooses.
Rats are better known, of course, as our immediate neighbours in cities, in towns, and on farms. Science defines the rat’s relationship to humans as commensal: an association between two species in which one benefits and the other is neither helped nor harmed. The label is awkward, however, since many people feel harmed by the mere existence of rats. When they shuffle and scratch in our walls at night, rats assail our mental health. Some feel physical disgust at the mere sight of rats’ ball-bearing eyes and maggot-coloured tails.
As one rat researcher recently put it in an interview with the New York Times, we tend to place rats in a “special category of things we don’t want to exist.”
We have responded with vigilantism. Humans’ relationship with rats is often described as the “war on rats.” But like our wars on drugs and terrorism, the war on rats has proved to be an unwinnable “forever war” — a term popularized, appropriately enough, in a 1974 sci-fi novel about a 1,000-year conflict between humans and an alien species.
It is a brutal war. A recent comment in an online forum about rat-catching captures the rules of engagement: “Worrying about how to kill rats ethically is of concern only to people who do not have a rat problem.” We do things to rats that most of us would find abhorrent, and would often be illegal, if they involved almost any other animal capable of feeling. We snap them in traps that can fail to kill instantly, leaving the animals maimed. We lure them into pails of water, where they swim until they can’t anymore, then drown. We bait them into patches of glue, where they tear skin and break bones in their efforts to escape, or even gnaw off their own limbs; some glue traps kill by slow suffocation. We use poisons against them that cause death only after days of painful internal bleeding. Online videos of people siccing dogs and minks on rats receive millions of views.
In a world at war with the rat, a defence of the enemy might seem hopeless. Yet the second reason to mount that defence is that there is new evidence in the rat’s favour. A growing body of research paints a picture of the accused that is far less vile than has been portrayed, and that may even charm the jury. To begin, we must dust off the closed case that marked rats with their original sin against us: the Black Death.
Has the black rat (Rattus rattus) been falsely blamed for spreading plague during the Black Death? Picture: Science Photo Library
In 1982, scientist Lars Walløe [published] what is now known as the “human ectoparasite hypothesis” of the plague’s spread—meaning that the illness swept across Europe not on a wave of rat fleas abandoning the carcasses of their rodent hosts but via human fleas and lice profiting from our own unhygienic habits and tendency to provide the poor with only squalid, unsanitary housing.
Walløe’s paper became something of a sleeper success and, in 1995, was printed in English. That brought his clash with the prevailing narrative to a much wider scientific audience, which reacted more with noise than substantial counterargument. “The response was very negative, but it wasn’t very strong,” Walløe recalls. “It was more like, ‘Here is a fool from Norway, and we don’t have to take him very seriously.’”
Since then, further lines of evidence have supported the human ectoparasite theory. In 2018, Katharine Dean, a Norwegian biologist, published research that modeled plague epidemics in nine European cities where detailed records were kept. They ranged in latitude from Stockholm, Sweden, to the Mediterranean island of Malta, and across time from 1348 to 1813. In seven of the nine locations, the spread of the disease fit best with human fleas and lice as the carriers; the other two outbreaks proved too small to clearly parse causes. A genetic study, meanwhile, found that plague was present in Europe for approximately 1,200 years without the presence of rats. Historical research notes that plague pandemics throughout Europe’s Little Ice Age (roughly 1300 to 1850) and in winter aren’t compatible with large, active populations of black rats or their fleas, both of which struggle in cold climates, not to mention outbreaks of “plague without rats” in medieval Iceland. The theory of rat-borne plague in medieval Europe now suffers in many places from what a 2021 paper published by The Lancet described as “the absence of its protagonist.” In the case of the notorious plague in Europe, the event that forever marked rats as public enemy number one, the animals may be almost entirely innocent.
“They are sweet, small animals,” Walløe says about rats. “I have nothing against them.”
Critics will point out that even if we exonerate the rat for the Black Death, it doesn’t mean rats are not verminous. It remains a historical fact that rats were patient zero in horrendous outbreaks of plague in warmer parts of the world, killing millions of people across centuries. Set aside plague altogether, which modern hygiene and medicine have rendered rare and curable across most of the world, and rats are still carriers of dozens of diseases with the potential to spill over to humans.
“They have this incredible sponge capacity,” says Chelsea Himsworth, a veterinary pathologist and epidemiologist in Abbotsford, British Columbia. “They traverse all sorts of different environments, they come into contact with microbes from humans, different domestic animals, sewage, garbage, et cetera, and then they have the ability to carry these pathogens and potentially transmit them back to humans or other animals.”
This is not, as it turns out, a blanket condemnation of rats. Himsworth’s interest turned toward the rodents more than a decade ago, as scientists began to focus on the potential disease risks presented by wildlife in environments like rainforests and grasslands. She looked instead at the research into rats and disease, and discovered little contemporary science on the subject.
“That struck me as particularly odd,” she says. “If people are going to come into contact with a wild animal, it’s more likely going to be a rat than something more exotic.”
In 2011, Himsworth founded the Vancouver Rat Project, a research body dedicated to better understanding the true disease risk that rats pose in British Columbia’s largest city, which the pest control company Orkin has named as Canada’s second “rattiest” metropolis, after Toronto. She has since drawn a stark conclusion about the perception that every rat we meet is a superspreader: “It’s inaccurate from a scientific standpoint,” she says.
To understand what patterns of disease in rats really look like, we first must confront the myth that rats are swarming invaders, a vision often promoted in books and film (a recent example appears in the Netflix hit Stranger Things). In fact, they tend to be homebodies. The Vancouver Rat Project found that, in a typical day, the city’s brown rats stay within the length of a city block. They generally do not cross roads, and research in other urban areas shows that rats even prefer to stick to one side or the other of alleys.
This means, Himsworth says, that even a ratty block of downtown Vancouver could have no diseased rats at all, while on another block every rat might carry sickness. For similar research in Vienna, Austria, published in 2022, researchers captured rats across two years at a popular riverwalk, a touristed square, and a cruise-ship port. They then tested them for eight types of dangerous virus known to be harbored in rats, including strains of hepatitis, coronavirus, hantavirus, and the influenza virus that causes global flu outbreaks. They found not a single rat that carried any of the diseases. The authors noted that studies that don’t find the presence of disease in rats are rarely published, and argued that this could lead to a “misconception of the reality”—a false belief that urban rats are all teeming with contagion.
Misconception is the order of the day with rats. Rats are aggressive, right? Bobby Corrigan, a legendary rodentologist and pest control expert in New York, has said that rats have never attacked him, “and I’ve put myself right in the thick of those animals, as thick as I can get.” But rats are filthy, right? In fact, they are such fastidious groomers, one scientist who researches laboratory animal welfare told me, that when she tried to use “permanent” ink to make identifying marks on rats’ tails, those marks were quickly cleaned away.
Even more surprising is how little we know about how often rats spread disease to humans. “We have no idea,” says Himsworth. She is, however, prepared to venture an educated guess. “Any rat you meet has the potential to have a disease,” she says. “But know that, in general, the risk—particularly for people in countries like Canada—is low.”
Most people in wealthier nations live in sturdy, clean homes and have the resources to respond if faced with a serious rat infestation. On the other hand, a person who is living, say, in poor-quality housing, whose hygiene is affected by mental health struggles, and whose landlord refuses to act as rat problems worsen, is definitely at an increased risk.
Furthermore, if our main concern is the real (if overweighted) risk of rat-borne disease, then our current tactics may be counterproductive. Killing rats with traps can disrupt their social structures, creating chaos in which rats may spread disease through behaviours such as fighting for dominance. A study in Chicago found that poisoning had a similar effect. Modern rodenticides kill rats in a process that may take five to 10 days. Live-trapped rats that had been poisoned were three times more likely than other rats to carry disease. The poison likely weakens their immune systems, making them more susceptible to illness.
“The interspecies genocide approach—it’s not effective, it’s never worked. It’s just silly to carry on the way we have been,” says Himsworth. “I also don’t think it’s good for us as people and as communities to be dealing with another species in that manner.”
The rat, meanwhile, isn’t just another species. It’s one that we might reasonably learn to see as a fitting companion for human society.
When it comes to rats winning your heart, let me not hold back: rats can learn to play hide-and-seek with humans. They will do so for no other reward than tickles and fun. And they will laugh.
This is not woo-woo hearsay but scientific fact. Researchers at the Bernstein Center for Computational Neuroscience in Berlin found that rats can learn, with surprising quickness, how to play both the “hide” and “seek” roles in games against a human experimenter. To ensure that the rats’ motivation was play rather than profit, the animals were not given food rewards when they found, or were found by, their human.
Instead, they were “tickled”—given a brief bout of light roughhousing by the researcher’s fingertips, which previous studies had shown that most rats enjoy.
The rats made eager playmates. When it was time to seek, they scampered out of a lidded box, carried out a systematic search of the game space, then beelined toward their quarry the moment they spotted the hider. When the rats were doing the hiding, some — behaving like human children —took off to hide again as soon as they were caught, lengthening the thrill of the chase.
The rats teased the humans. They performed freudensprung, a German word that means “joy jumps.” They also emitted the kind of ultrasonic chirps that have been linked to what scientists dryly call “positive affective states.” (“You can say it’s laughter, but it’s not sounding really like human laughter,” says Sylvie Cloutier, an ethologist who pioneered research into rat tickling but was not involved in the hide-and-seek study. “They’re more like little happy chirps when you can hear them.”)
After the experiment, and rather chillingly, the researchers euthanized the rats that played with humans in order to further study their brains.
Paradoxically, much of what we now know about rats’ emotional and intellectual worlds is grounded in the fact that we experiment on them. A cottage industry of breeding brown rats for use in laboratory experiments emerged in Europe in the 1840s, making rats the first mammal to be domesticated mainly for scientific purposes. Industrial-scale production of “lab rats” began in 1906 at the Wistar Institute of Anatomy and Biology in Philadelphia, Pennsylvania. Even today, nearly half of all lab rats descend from the original Wistar colony. They are mainly albinos, favored for their genetic uniformity and calm dispositions.
At the outset, Wistar researchers Milton Greenman and Louise Duhring sought to make lab rats “contented and happy.” Their animals were “carefully gentled” to human handling and ate a diet that ranged from macaroni to kale to breakfast sausages, or even hot cocoa if a rat was feeling under the weather. The rodents enjoyed abundant direct sunlight—“unfiltered through glass windows”—and fresh air. “Most albino rats,” they noted, “are susceptible to the soothing influence of soft, sweet music, especially the higher notes of the violin.”
The rats’ cages included some amenities. Each was furnished with material the rats could burrow in and had one of those exercise wheels familiar from hamster cages, except that the wheels were the size of bicycle wheels. The rats often spun the equivalent of more than eight kilometers a day in them.
A century later, modern lab-rat life is defined by what’s known as the “shoebox” — a cage too small for rats to carry out such natural behaviors as burrowing, climbing, or even standing upright. No more hot chocolate, they mainly eat a standardized laboratory rat chow. An estimated three million rats are used in laboratory experiments each year in the United States alone, with about 1.2 million of those experiments classified as painful or distressing.
Over time, scientists’ use of rats as test subjects began to reveal the possibility that rats, and therefore other animals, have qualities previously thought to be the exclusive domain of human beings.
In 1959, American experimental psychologist Russell Church found that rats learned to stop pressing a lever that provided them with a tasty treat when doing so also delivered an electric shock to a rat in an adjacent cage.
It was the first study to suggest that rats might recognize when one of their own kind was suffering and alleviate that suffering if they could.
The debate about whether rats and other animals really care about others or only act in ways that resemble empathy has gone on ever since. But picture this recent study: Rat A is safe and secure. Rat B is distressed, because it’s in a separate chamber where it has no option but to stand in a pool of water. Rat A will release Rat B from that chamber even if liberating Rat B does not provide Rat A with access to the water, or the other rat, or any kind of reward.
It becomes difficult to propose motivations for Rat A that don’t involve a capacity to put itself in Rat B’s position.
Scientists who claim that animals share human qualities like empathy are often condemned for anthropomorphism — the sin of awarding human characteristics to things that are not human. In 2021, two researchers from the Medical University of South Carolina reviewed the numerous studies on empathy in rats and concluded that refusal to recognize the rodents’ empathic abilities now amounted to “anthropodenial”, a term coined by primatologist Frans de Waal in 1997 to refer to a stubborn tendency to dismiss humanlike characteristics in animals, no matter how convincing the evidence.
Other laboratory experiments have shown that rats can solve complex puzzles, recognize cause-and-effect relationships, feel regret, make judgments based on perception, and understand time, space, and numbers. In online videos posted by owners of pet rats, you’ll find trained rats completing agility courses, raising tiny flags by pulling tiny ropes with their delicate fingers, and “reading” placards that instruct them either to jump onto a box or spin around. Rats even appear to engage in metacognition, meaning rats know that they think.
Rats have personalities, too. Nearly every researcher I spoke to who had worked directly with the animals recalled individuals whose distinctive way of being in the world stands out in their memories. Lazarus, for example, was a favourite of Kaylee Byers, who captured and released about 700 different rats for the Vancouver Rat Project. As the rat’s name suggests, Byers thought Lazarus was dead when she first found him motionless in one of her traps. It turned out he was simply unusually chill. After being captured that first time, he returned to be caught again and again. He would eat the peanut-butter-and-oats bait, then wait to be released, apparently grasping that Byers would do him no harm.
If rats have begun to remind you of another animal—you know, the one we increasingly treat with overweening kindness and respect, and rarely hesitate to anthropomorphize—then, well, there’s good reason for that. Joanna Makowska, an animal welfare scientist, remembers a veterinarian once sharing with her the advice he gives to people who are looking for a very small dog. “He tells them, ‘Get a rat.’”
If the rat was not the bête noire of the Black Death; if it poses a low risk of disease in many places, and, where it is poses a higher risk, is a better reflection of how poorly our societies care for the vulnerable than the real dangers of the animal itself; if the rat is not aggressive or filthy; if the rat is not a shadow of our worst qualities but instead can reflect our best; and if—perhaps most important of all—we cannot win our cruel war against them, then an obvious question remains. What are we to do about rats?
The surprising answer may be this: communicate with them.
“If we don’t want rats in the area, we should be more mindful of the signals that we’re sending to them, which are like, ‘Hey, there’s a bunch of food that we don’t really care about, and we usually put it out here at this time,’” says Becca Franks, an assistant professor in environmental studies at New York University who has studied rats and once had a wild rat gnaw through the wall of her home. “If we don’t actually want them there, I don’t think that’s the message that we’re sending in a way that they understand.”
The real, lasting solution to rats damaging our homes and eating our food, Franks says, is “unsexy infrastructure stuff.” Design buildings to exclude rats. Put garbage in rat-proof containers, as New York is only now beginning to require. Pass bylaws that give tenants the right to live in rat-free housing, holding neglectful landlords to account. If the scale of such changes seems overwhelming, history provides inspiration.
In the 1920s, mariners made a hard turn toward rat-proofing their boats. This required thinking like a rat, said anthropologist Jules Skotnes-Brown: blocking their runways, storing food in impenetrable containers, and closing out hollows and nooks used for nesting. One early success reduced the rat population on a ship from 1,177 to zero. Through a combination of financial incentives and government regulations, rat-proofed ships were widespread by the mid-1930s.
We are relearning how to coexist with other wildlife species that were once dismissed as vermin or “man-eaters,” including wolves and bears, coyotes and beavers. Along the way, we’re finding that, as Aldo Leopold put it, “Wildlife management is comparatively easy; human management difficult.” Bears can be excellent neighbours, but not if they’re hooked on eating garbage from bins they can easily break into. Wolves can live almost unseen alongside us, but not if we feed them by hand to get a good selfie. Rats can be our shadow companions, but not if we openly discard so much food that some rats—and this is true—develop a taste for Chinese over Italian, or vice versa.
But Franks is prepared to imagine forms of communication that go beyond unsexy infrastructure and antilittering campaigns.
Franks recalls visiting a researcher who kept her lab rats in a small room. The researcher closed the door behind them, then opened the rats’ large cage. Scenes that seemed clipped from the film Ratatouille began to play out. The rodents, about 15 in all, tumbled out onto a table, then streamed down its legs to the floor. A few climbed one after another up a broomstick to the top, where the uppermost rat suddenly let go, sending every other rat playfully sliding down. The researcher used a bat detector to listen in on the rats’ ultrasonic voices. They could hear them, “chittering and laughing and squealing and having just a wild time,” says Franks.
Suddenly, Franks realized she had another meeting to get to, and here she was in a room full of free-ranging rats. She couldn’t just open the door and leave—rats would surely escape. But catching each rat and putting it back into the hutch would take forever.
“I think, you know, we should probably get them back in the cage,” Franks said.
“Oh, okay,” said the researcher.
She opened the cage door. The rats streamed back up the table legs and into confinement, where they continued to romp and play. Franks made it to her meeting.
It was an example of how building relationships and channels of communication with rats might allow us to come to understandings with them. “Rats can be quite responsive to human interests that potentially are not even in alignment with what the rats want,” said Franks.
I admit, and so does Franks, that we are entering unexplored territory here. What does it look like to form social relationships with wild rats? Do we hire rat-catchers who tickle rather than kill? Draw hard territorial lines where they’re most important—in homes, offices, restaurants—while accepting rats on a downtown street or in a park in the same way that we do a pigeon or any other commensal animal?
An idea that seems absurd is sometimes a truth that we haven’t yet accepted. Years after de Chasseneuz represented rats in the court of Autun, one of the strangest animal prosecutions on record gave hints of how the famous lawyer might have fully defended the rats had their trial proceeded.
The case in question was launched against beetles of the species Rhynchites auratus—handsome golden-green weevils—in Saint-Julien, France, in 1587. As with the rats of Autun, the accused were charged with ravaging crops, this time the local vineyards. Again, counsel was appointed to defend the verminous pests.
The prosecution relied on Biblical passages that give humankind dominion over “every creeping thing that creepeth upon the earth”: since weevils surely creepeth, we were free to decide their fates. The defense, meanwhile, made the case that weevils were a part of divine creation, and God had made the earth fruitful “not solely for the sustenance of rational human beings.”
The trial lasted more than eight months, and at one point the restless citizens of Saint-Julien offered to mark out an insect reserve where the weevils could feed without harming the vineyards. The weevils’ advocates were not placated. They declared the land inadequate, turned down the offer and, as lawyers will, sought dismissal of the case, with the accusers paying the weevils’ legal costs.
No one today knows how the matter was finally decided, because the last page of the court record is damaged. It appears to have been nibbled by rats or some kind of beetle.
Preposterous? Absolutely. Yet by putting weevils on trial, both defense and prosecution came to agree on one point that eludes us today: creatures have a right to exist in accordance with their nature, even if it is their nature to make trouble for humankind.
