Rats: the planet's most tenacious survivors with a lot to teach humanity
For centuries, rats have been vilified and feared. But in truth they are empathetic and rarely aggressive
*Originally published on October 26, 2020.
Is there any creature that inspires more hatred and fear than the rat?
For centuries, they've been reviled as destroyers of food supplies, associated with disease, and cast as the nightmarish villains of stories ranging from Edgar Allen Poe's 19th century short story The Pit and the Pendulum to the 1971 cult horror classic Willard.
But rats are more complex than their representation in popular culture often suggests, and if you trace the roots of humanity's rat problems back to their source, you can see they often start with people.
Take a standard alleyway, where in almost any city on the planet there's a good chance of finding rats; over the long history of cohabitation with humans, rats have adapted to thrive in urban environments.
"The ideal environment for rats in cities is actually not difficult to put together," says Bobby Corrigan, an urban rodentologist based in the New York area. "First, it starts with food."
For this purpose, an overflowing garbage bag will do nicely.
"Of course, after food, then we're going to have a situation where they need a home, just like we do."
That can be provided by the crumbling foundation of the buildings on either side of this alley — after squeezing through a hole in that foundation the size of a quarter, a rat can raise up to seven litters a year in a space no bigger than a basketball.
"Now you have good food. You have good places to build a nest, and once you put those two big pieces together, you're pretty much in the perfect storm, if you will, for rats rearing themselves in great numbers."
Following humanity's footsteps
Around the world, rat numbers appear to be on the rise, aided by the conditions of the 21st century: warming temperatures due to climate change, and increasing urbanization.
But this relationship goes back much farther than the present day.
Rodents first emerged roughly 56 million years ago. Black and brown rats — the kind of rats most associated with people — likely originated in India and Mongolia, respectively. They are now found on every continent except Antarctica, having followed in humanity's footsteps for millennia.
In some places, rats garnered positive associations. The Karni Mata temple, in Northern India, is home to more than 25,000 rats, with the white rats among them revered as descendents of the 14th century sage Karni Mata — herself an incarnation of a Hindu goddess — and her sons.
And in the Chinese zodiac, the sign of the rat is associated with ambition, intelligence, and charm.
In medieval and early modern Europe, which black and brown rats had reached by hitching a ride on trade routes, rats' ability to exploit human environments made them a practical and spiritual foil to people.
"Every castle, every community had a priest, but also a rat catcher, and this rat catcher was a kind of semi mystical figure, like a vermin whisperer," says Lucinda Cole, a research associate professor at the University of Illinois.
This antagonistic relationship was particularly heightened in the 16th century, when a "little ice age" descended over Europe, and food supplies shrunk, making rat infestations an increased threat to the survival of the community. Part of this was due to rats' exponential rate of reproduction, which also informed beliefs about rats' moral corruption.
"A sexuality that reproduced so rapidly — and turned two creatures into a swarm often, you know, in a month — that was going to be a source of threat," says Cole.
"But I think symbolically it was also perceived as threatening, and you can look at some of the literature and see the ways in which rats were associated with promiscuity, often a kind of disgusting promiscuity."
This situation only got worse as rats stowed away on ships piloted by Europeans, who were setting out to subjugate much of the rest of the world. As rats hopped or swam ashore wherever these ships landed, they destroyed food supplies, decimated native biodiversity, and spread disease.
In some cases, even colonial attempts to prevent the spread of disease favoured rats. In the early 20th century, brown rats originally from south China, bearing bubonic plague, spread through Hanoi in the sewer system French colonizers had built to counter cholera.
"What was supposed to be a technological fix, to solve health crises in Hanoi, actually created an entirely new and potentially much more serious health problem," says Mike Vann, professor of history at California State University, Sacramento, and author of The Great Hanoi Rat Hunt: Empire, Disease, and Modernity in French Colonial Vietnam.
Measures to contain the rats backfired as well. French authorities offered the Vietnamese a penny per tail, which seemed to be working — until they realized people were cutting off rats' tails, while letting the creatures run free to produce more rats.
These efforts were only part of a global campaign against rats being waged at the time, as officials sought to contain a pandemic of bubonic plague.
The third plague pandemic, which began in the Chinese province of Yunnan in the mid-1800s, killed roughly 12 million people worldwide in the late 19th and early 20th centuries. It also happened just as humans had come to understand the role of animals — including rats — in spreading disease.
This discovery didn't only spark global efforts to stop the spread of rats; it also had long-lasting impacts for how we understand infections that can jump from animals to people, which include everything from bubonic plague to COVID-19.
"The study of the rat and the efforts to control it, and the feedback between practical efforts on the ground and science created many of the notions we have today, about zoonotic diseases," says Christos Lynteris, principal investigator of a Wellcome funded project called The Global War Against the Rat and the Epistemic Emergence of Zoonosis.
Rat versus human brain cell
Even as people were coming to better understand the negative impacts of rats on public health, rats were also starting to play a significant role in biomedical research.
Rats have been used in laboratories since the 19th century. They're now used in research on conditions ranging from cardiovascular diseases to cancer.
But where they may be most useful is in shedding light on the human brain and behaviour, says Kelly Lambert, behavioural neuroscientist and professor at the University of Richmond.
"If you look at a brain cell in a rat, under a microscope, and a brain cell in a human, you can't tell the difference. It has all the same structure; they use the same neural chemicals. It's a very good scaled down model of a mammalian brain," Lambert says. "And it engages in behaviours that I'm interested in: stress responses, parenting, and learning."
Research in Lambert's lab has included the impact of reduced resources on rat mothers and their litters, and whether or not rats can learn the complex task of driving tiny cars, in return for fruit loops.
Lambert says the studies on driving have also underscored the significant role of environment — in this case, enriched cages, with more space and stimulation for the rats, versus standard cages, which are Plexiglas boxes — in brain development.
"I have been just shocked, actually, to see that the animals that were kept in standard laboratory cages — which is where we keep most of our laboratory animals — some of them just can't learn to drive. They're not comfortable even getting in the car. They're not accepting the reward," Lambert says.
"So that says something about fear and about how complexity in our environment gives us a greater sense of control, so that we can try these new things and engage in new forms of learning."
To draw greater insights about the human brain from rats, Lambert says researchers should consider housing for lab rats in more stimulating environments, which would allow them to exercise the adaptable, intelligent natures they share with their wild ancestors.
And when it comes to managing the wild rats inhabiting our cities — especially as cities grow, and rat populations follow suit — more researchers are saying it's important to consider their living conditions too.
"Right now, we're so focused on just eliminating rats themselves, without acknowledging that rats are a part of our cities, they're part of our ecosystems," says Kaylee Byers, with the Vancouver Rat Project, which was founded in 2011 by veterinary pathologist Dr. Chelsea Himsworth to look at rat-associated health risks in Vancouver — and to examine the little-understood ecology of urban rats.
"So I think, instead of focusing on, let's just remove all rats everywhere, let's think about, what are the vulnerable aspects?" says Byers. "Where are those interfaces where we can actually develop and deploy management methods to mitigate those risks?"
This could mean moving beyond trapping and poisoning strategies humans have used for centuries — and which the Vancouver Rat Projects's research suggests, may sometimes make rat problems worse, by creating more opportunities for pathogen spread between rats — and instead focus on where rats cause the most harm, including to those who are homeless or living in substandard housing.
Urban rodentologist Bobby Corrigan says it also means turning the mirror on ourselves — not only to recognize how human behaviour, such as with our careless disposal of trash, creates rat problems, but also to interrogate assumptions about rats being vermin, unworthy of serious consideration or humane treatment.
"I do see change. I've seen just my own world the past five years, a whole lot more graduate students in rodents than I've ever seen before," Corrigan says.
"And to some degree, rats, then, we owe our, you know, appreciation of that animal. We owe our respect to that mammal."
Guests in this episode:
Bobby Corrigan is an urban rodentologist based in the New York area.
Lucinda Cole is a research associate professor at the University of Illinois and the author of Imperfect Creatures: Vermin, Literatures, and the Sciences of Life 1600-1740.
Mike Vann is a professor of history at California State University, Sacramento, and author of The Great Hanoi Rat Hunt: Empire, Disease, and Modernity in French Colonial Vietnam.
Christos Lynteris is a medical anthropologist at the University of St. Andrews and Principal Investigator of a Wellcome funded project called The Global War Against the Rat and the Epistemic Emergence of Zoonosis.
Kelly Lambert is a behavioural neuroscientist at the University of Richmond and the author of The Lab Rat Chronicles: A neuroscientist reveals life lessons from the planet's most successful mammals.
Kaylee Byers did her PhD with the Vancouver Rat Project and is Deputy Director of British Columbia's Canadian Wildlife Health Cooperative.
Natalie Kofler is a molecular biologist by training and the founder and director of Editing Nature, an initiative to encourage conversations about the ethics and regulation of new genetic technologies.
Jan Zalasiewicz is a professor emeritus of palaeobiology at the University of Leicester.
*This episode was produced by Moira Donovan and Mary Lynk.