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In a surprising discovery, John Gladwin found a torn bag of soil under his kitchen sink one morning last year, prompting an investigation into the cause.

The presence of a strong, musty odor soon followed, reminiscent of the smell often found near communal trash areas.

John Gladwin's immediate reaction was, "I knew what it was straight away – rats."

Having previously spotted rats near the bins, he realized they had now invaded his home.

The sounds of rats scurrying in the cupboards and behind the bath panel, as well as the noise of them fighting under the bath, were unmistakable.

Taking swift action, Mr. Gladwin used peppermint oil and rat poison, successfully deterring the rats from returning, but the experience left him shaken, particularly due to concerns for his five children's health.

Additionally, he felt a sense of embarrassment about the situation.

Admitting to a rat infestation in one's home can be difficult, as it may be perceived as a reflection of the family's living conditions.

Cleankill, a pest control company, has reported a significant increase in rat-related callouts, with founder Clive Bury estimating a 20% rise over the past two years, primarily in the southern region of England.

Similar trends are being observed nationwide, with the British Pest Control Association noting that over half of its member companies have seen an increase in rat infestations over the past five years.

Due to their nocturnal nature and ability to live in hidden areas such as drains and sewers, accurately counting rat populations is challenging, with estimates ranging from 10 million to 120 million in the UK.

According to data gathered by Drain Detectives through Freedom of Information requests, more than 500,000 rodent infestations were reported to UK councils between 2023 and mid-this year.

The issue is not limited to the UK.

Several major cities, including Washington DC, San Francisco, New York City, Amsterdam, and Toronto, have also experienced a surge in rat populations.

As rats often scavenge in sewers and trash, they can transmit diseases such as leptospirosis and hantavirus to humans, highlighting the need for effective control measures.

Considering the difficulties in eradicating rats, it is essential to explore strategies for mitigating their impact on urban areas.

Bobby Corrigan, an expert in urban rodentology, has spent his career studying rats, from his early days as an exterminator in New York City to his current research endeavors.

His work has taken him to unusual locations, including sewers, where he has attempted to use poison baits to control rat populations.

During his academic pursuits, Corrigan went to great lengths to understand rat behavior, even sleeping in a rat-infested barn to observe them firsthand.

His observations revealed a complex social structure among rats, with evidence of altruistic behavior, such as young rats sharing food with older, less mobile individuals.

Corrigan is determined to understand the factors contributing to the rise in rat populations.

Several possible explanations have been proposed, including the growing demand for fast food, less frequent trash collection, and construction projects that disrupt sewer networks.

Additionally, research suggests that rising temperatures may also play a role in the increase in rat populations.

A study conducted by Corrigan and researchers from the University of Richmond found a correlation between temperature increases and rat activity in 16 cities, mostly in North America.

The results, published in Science Advances, showed significant increases in rat activity in 11 cities, with Washington DC experiencing a nearly 400% rise, San Francisco a 300% increase, and New York a 160% surge.

Only three cities, including Tokyo and New Orleans, saw declines in rat populations.

The study found that cities with greater temperature increases had larger rises in rat activity, with some areas experiencing temperature increases of up to 2C.

Corrigan believes that as temperatures continue to rise, particularly during winter months, the growth in rat populations is likely to persist.

According to the Climate Action Tracker, global temperatures are expected to rise by at least 1.9C and up to 2.7C above pre-industrial levels by 2100.

Rats are prolific breeders, with females producing up to six litters per year, each containing up to 12 pups.

These offspring can begin breeding after just nine weeks, allowing two rats to potentially produce over 1,000 descendants in a single year.

Urban areas, with their heat-trapping buildings and tarmac, tend to warm more quickly than rural areas, creating an ideal environment for rat populations to thrive.

The trend of people moving from rural areas to cities also contributes to the growth in rat populations, as it reduces their natural habitat and creates more opportunities for them to infest urban areas.

The increasing number of buildings and infrastructure in cities provides rats with more places to live and hide, making control efforts more challenging.

One interesting fact about rats is their inability to vomit, which, in theory, should make them more susceptible to poison baits.

However, rats are also neophobic, meaning they are cautious of new things, and this trait may be related to their inability to vomit, according to Professor Steven Belmain.

This cautious approach to life allows rats to avoid potential dangers, making them more resilient to control measures.

Rats will only try a small amount of a new food source before deciding whether it is safe to consume, demonstrating their adaptability and ability to thrive in various environments.

This unique combination of traits has enabled rats to survive and prosper in a wide range of settings, making them a formidable challenge for control efforts.

With three decades of experience under his belt, Dr. Alan Buckle from the University of Reading has dedicated his career to developing innovative rat poisons, but he admits that his efforts have been unsuccessful.

Rats are known to avoid substances that cause discomfort or pain, which is why anticoagulants, a type of poison that prevents blood clotting, are commonly used as they are slower-acting and allow rats to consume a lethal dose over time.

However, these substances can take up to a week to be effective and are considered inhumane as they cause internal bleeding, leading to a slow and painful death for the rats.

Furthermore, rats have developed genetic mutations in recent years, rendering them partially resistant to these potent drugs.

Researchers are exploring alternative methods, including the use of oral contraceptives, as a more humane approach to controlling rat populations.

Kathleen Corradi, who was appointed as New York's Rat Tsar by the Mayor in 2023, is all too familiar with the challenges of tackling rat infestations.

It's estimated that approximately three million rats inhabit the five boroughs of New York, and Corradi was allocated $3.5m (£2.6m) to increase public awareness about rat mitigation strategies.

Corradi established a "rat academy" to educate residents on how to prevent rat infestations in their neighborhoods.

As part of the academy, Corradi takes participants on a "rat walk" through neighborhoods, discussing both human and rat behavior and how they intersect.

The goal is to empower residents with knowledge on how to prevent rat infestations and take action in their own communities.

Corradi's team also encouraged residents to report rat sightings or evidence of rat-attracting behavior, which would prompt inspections and potential fines for non-compliance.

A key aspect of the initiative was the introduction of rat-proof bins, replacing traditional plastic bags, to reduce the availability of food sources for rats.

Although Corradi is stepping down from her role, she reports that the approach is showing promising results.

According to Corradi, the key to sustained reduction in rat populations lies in cutting off their access to food sources.

In Croydon, pest controller Alex Donnovan from Cleankill led an early-morning excursion to the backyard of an estate where John Gladwin resides, demonstrating the extent of the rat infestation.

As we stood still and quiet, a rat emerged from beneath the concrete walkway and scurried towards the communal bins, followed by another rat that appeared from a burrow at the end of the garden.

During our two-hour observation, several rats were seen climbing trees and one even jumped into a bin, rummaging through a plastic bag for food just meters away.

Donnovan believes that gaining control over such a severe infestation is nearly impossible, citing the abundance of food as a major obstacle.

He noted that even if rodenticide is used, the rats are unlikely to consume it due to the availability of alternative food sources, and the infested bins often become a deterrent for waste collection.

While warmer temperatures may contribute to growing rat populations, factors such as overflowing bins, fast food waste, and social fragmentation exacerbate the challenge of controlling rat infestations.

The UK's population is projected to increase from 67.6 million in 2022 to 72.5 million by 2032, with a growing proportion of people living in urban areas, according to the Office for National Statistics.

Instead of relying on poison, a more straightforward solution might be necessary to address the issue.

Dr. Corrigan argues that by taking care of the urban environment, the need for inhumane methods of rat control can be alleviated.

By denying rats access to food and scraps, the need for poisoning, killing, and torturing them can be avoided, according to Dr. Corrigan.

The challenge now is to implement this approach quickly, as Dr. Corrigan notes that the issue has been underestimated and neglected, allowing rat populations to spiral out of control.

The consequence of underestimating and ignoring the rat problem is now being felt, and it's essential to take action to address the issue.

Additional reporting for this article was provided by Florence Freeman.

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