Rats! Why Toronto’s rat population is growing, and will likely continue to do so

Rats swarm around a bag of garbage near a dumpster in New York, July 7, 2000. (Robert Mecea / AP Photo, File)

Toronto may need to change how it plays its game of cat and mouse with its growing rat problem.

A new peer-reviewed study, published in Science Advances, took a closer look at public rat sighting and inspection data from more than a dozen cities across the globe over the last 12 years.

Of the 16 cities researchers investigated, 11 saw significant increases to their “rat numbers” with Toronto ranked third, behind only Washington and San Francisco.

Toronto even squeaked past New York City – whose rat problem became so severe that it now employs a “rat czar” – for third.

“I’m not really surprised. There have been rats since, I think the earliest reports were back in the early to mid-1800s,” Burton Lim, assistant curator of mammals at the Royal Ontario Museum, told CTV News Toronto.

“As the population has gotten bigger, there’s more food available. This is a particular species of rat (Rattus norvegicus and Rattus rattus) that just does well wherever people are, so feeding primarily off the garbage but also taking advantage of nice, warm homes that they can also live in.”

The prevalence of rats in Toronto has been on the rise for years and the research suggests that the city will likely see more of these rodents in its streets due to warming temperatures and its densely-populated urban centre.

Alice Sinia is an entomologist and pest specialist at Orkin Canada. She says the data underscores what the pest control company has already been seeing.

Orkin Canada had already crowned Toronto as the “rattiest” in Canada for the last few years.

“Over the years we’ve seen a steady increase in, I would say, unscientific population among rodents in Toronto,” Sinia told CTV News Toronto. “The reason I’m saying its unscientific is because it’s within our industry, the structural pest control industry. We’ve been getting more calls and services for rodent control.”

The study notes a major contributor for the rise of rats is largely linked to the weather, as cities with a “greater rise in temperature over time had larger increases in rat sightings.”

A recent analysis by non-profit research group, Climate Central, suggested Toronto lost nearly two weeks' worth of freezing winter days due to climate change over the past decade from 2014 to 2023. To determine this, they counted the number of above-freezing days over the last decade compared to a world without fossil fuel emissions. Globally, the peer-reviewed rat study noted the average rate of warming has been 0.2 C per decade since 1975 and while it is accelerating, that same rate is not felt universally.

Sinia explains cold winter weather is like a “natural pest control.” Though rats can regulate their body temperature, they cannot maintain it in freezing temperatures and are forced to take cover in freezing conditions.

Since the winters are milder, Sinia says rats don’t have to hide and can stay above ground for longer to scavenge for food.

“That means they’re able to expand in other areas, and they’re able to forage longer, they’re able to reproduce longer and able to produce more litters, and that drives up the population,” Sinia said.

Outside of climate warming, the study found population density and urbanization as other major contributors to how rats thrive in a city.

Toronto and the surrounding region’s population cracked more than 7.1 million as of July 2024, according to a Statistics Canada, up nearly four per cent from 2023.

“We know that population growth goes hand-in-hand with resources, so when there’s food, the rats are able to reproduce faster because that means the resources are able to sustain that population,” Sinia said.

Sinia also pointed to the increased construction in Toronto as a breeding ground for rats.

“When they build, they have to break up the soil, the ground, they have to disturb the natural ecosystem,” Sinia said.

“Now they are being displaced from their natural, outdoor system. So, where do they go? They are pushed indoors, they are pushed into commercial structures, so that displacement actually brings the rats more in contact with humans so that means we end up seeing more rats.”

What is Toronto’s rat action plan?

The new study comes as Toronto City Council continues to look at ways to reduce the growth in the city’s rat population.

Last July, Coun. Alejandra Bravo and Deputy Mayor put forward a motion to craft an “action plan” to reduce the rat population in the city.

“As climate change, construction site management, infrastructure state-of-good-repair, solid waste management practices, property maintenance and many other factors accelerate the presence of rats in our neighbourhoods, we believe it’s time for Toronto to take this step,” the councillors wrote in a letter to the Infrastructure and Environment Committee, imploring them to consult with other North American jurisdictions on how to develop a rat reduction strategy.

Alberta, for example, has been a designated rat-free province for more than seven decades through its Rat Control Program, and Ottawa has recently put forward a motion to explore a form of rat birth control – ContraPest – which is not yet legal in Canada.

A City of Toronto spokesperson said it currently uses various methods to mitigate rodent-related issues in the city, including addressing complaints about garbage attracting rodents to private homes, investigating rat infestations, using pest control services to monitor and fill bait stations at city facilities, and having Toronto Public Health crack down on rodents in restaurants and other establishments carrying food.

“Like most major cities, rodents are common in Toronto. While the City of Toronto is unable to track the total rodent population in Toronto, the municipality is always open to looking at new ways to improve services it provides to residents and will continue to refine and improve its rodent control operations,” the statement reads.

With files from The Canadian Press