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Last year, John Gladwin opened a cupboard beneath his kitchen sink and discovered a bag of soil shredded into tiny fragments. Immediately, a pungent, musty odor permeated the air, resembling the smell near communal trash receptacles in his apartment building. "I knew exactly what it was," he recalled. "Rats." Although he had previously observed them scurrying near waste bins, they had now breached the sanctuary of his home. "I heard them moving within the cupboards and behind the bath panel. One morning, upon waking, I found them fighting beneath the bathtub, screaming and squealing." Mr. Gladwin resides in Croydon with his five children. He acted swiftly by dispersing peppermint oil and rat poison in the affected areas. Fortunately, the rodents have not returned. The ordeal left him deeply shaken. "I was terrified for the children's health. I did not want them contracting any diseases." He also experienced a profound sense of shame. "It is difficult to admit that we are infested, that our family lives in a rat-infested property."
Cleankill, a pest control firm operating across southern England, has been contracted by Mr. Gladwin's estate. Clive Bury, the company's founder, reports a dramatic surge in calls regarding rat activity. He estimates a twenty percent increase in inquiries over the last two years. Similar trends are emerging throughout the nation. The British Pest Control Association indicates that more than half of its member companies have experienced a rise in rat-related calls over the past five years. Rats inhabit drains, sewers, and burrows, primarily emerging at night, which makes accurate counting nearly impossible. Estimates of the UK rat population vary significantly, ranging from ten million to one hundred and twenty million. What is certain is that over half a million rodent infestations were reported to UK councils between 2023 and mid-2024, according to data collected by Drain Detectives.
This phenomenon is not confined to the United Kingdom. Rat populations have surged in several American cities, including Washington DC, San Francisco, and New York City. Populations are also rising in Amsterdam and Toronto. Rats are not inherently unclean animals, yet they scavenge in sewers and trash bins. They can transmit serious diseases to humans. Leptospirosis, also known as Weil's disease, spreads through their urine. Hantavirus can be transmitted when individuals inhale infected droppings. They also consume farm produce and can contaminate entire food supplies. Given that rats are exceptionally clever at evading capture, what measures could effectively halt their expansion? Are we already too late to prevent them from overrunning our cities?
Bobby Corrigan identifies himself as an urban rodentologist. He began his career as an exterminator in New York City and has dedicated his life to studying rats. "I found myself in sewers, attempting to hang poison baits to eliminate rats," he reminisced. Years later, while studying rats in college, he undertook extreme measures to understand their behavior. He once slept on the floor of a rat-infested barn to observe them firsthand. He was astonished by their complex social structures and signs of altruism. "I witnessed young rats carrying food and providing it to older rats that could no longer move," he remembered. He sought to understand the reasons behind the rising rat numbers.
Several factors contribute to this surge. Niall Gallagher, a technical manager at the British Pest Control Association, points to our increasing appetite for fast food. He also notes that some councils collect trash less frequently. Road and construction work that disturbs sewer networks also plays a significant role. However, evidence suggests that rising temperatures are a primary driver. Dr. Corrigan and researchers from the University of Richmond in Virginia studied whether rat activity correlates with temperature increases. Their research examined sixteen cities, mostly in North America. The results, published in the journal Science Advances earlier this year, found that eleven of these cities recorded significant increases in rat activity over seven to seventeen years.
In Washington DC, the increase was nearly four hundred percent. In San Francisco, it was three hundred percent. Toronto saw an eighteen percent rise, and New York witnessed a one hundred and sixty percent rise. Only three cities, including Tokyo and New Orleans, experienced declines. "Cities experiencing greater temperature increases over time saw larger increases in rats," the study concluded. In some locations, temperatures rose nearly two degrees Celsius during the study period. Dr. Corrigan believes that as long as temperatures continue to rise and winters become warmer, the increase in rat numbers will likely persist. Global temperatures are projected to rise between 1.9 and 2.7 degrees Celsius above pre-industrial averages by 2100.
Rats are phenomenal breeders. A female typically produces around six litters annually, with up to twelve pups per litter. Rats can begin breeding after just nine weeks. This means two rats could potentially generate more than one thousand offspring in a single year. Researchers note that numbers increase particularly in cities. This is because heat-trapping tarmac and buildings warm up faster than rural areas. The trend of people migrating from rural regions to cities also contributes. Dr. Corrigan explains, "Land is disappearing rapidly, and we are constructing buildings that reduce their habitat in the wild." More buildings create more nooks, pipes, and drains for rats to inhabit, adding to the challenge of controlling their populations.
A curious fact about rats explains why poison baits often fail: they cannot vomit. Theoretically, once they ingest poison, they cannot expel it. However, rats are also "neophobic," meaning they are fearful of new things. Professor Steven Belmain, an ecology professor at the University of Greenwich, states that these two traits are interconnected. "It is somewhat of a superpower," he says. When they discover potential food, they do not dive in immediately. "They will only sample a small amount. Once they understand they do not feel ill, they realize, 'Okay, I can eat that'. You could argue this cautious approach to life has served them well." Dr. Alan Buckle of the University of Reading has spent thirty years developing new rat poisons. He admits with a laugh, "I failed." If a poison tastes bad or causes pain, rats will not consume more. This is why slower-acting substances, primarily anticoagulants, are used. These drugs prevent blood from forming clots. They take up to a week to act, giving rats time to consume a lethal dose. However, this is a cruel method of death, causing internal bleeding.
In recent years, rats have developed genetic mutations that grant them immunity to these powerful drugs. Some researchers are now exploring oral contraceptives as a more humane method to curb rat population growth. Few understand this challenge better than Kathleen Corradi, a former schoolteacher appointed the city's Rat Tsar by the New York Mayor in 2023. An estimated three million rats inhabit the five boroughs. Corradi was awarded $3.5 million to increase public awareness regarding rat prevention. She launched a "rat academy" to teach residents how to stop their neighborhoods from being overrun. "They take a rat walk with me," she explained. "We venture into neighborhoods to discuss human behavior and rat behavior. We examine how these factors converge and what actions residents can take." Her team urged New Yorkers to report rats or behaviors that attract them. Inspectors investigate and order action, with substantial fines for non-compliance. A crucial change required residents to use rat-proof bins instead of plastic bags. Corradi is leaving the role but says the approach demonstrates progress. "Cutting off rats' food source is the key to a sustained reduction," she explained.
Back in Croydon, Alex Donnovan, a pest controller for Cleankill, leads me into the backyard of the estate where John Gladwin lives. It is just after dawn. He gestures for me to remain still. Moments later, a rat darts from beneath a concrete walkway toward the communal bins. Then, the head of a large rat emerges from a burrow at the end of the garden. During the two hours spent on the estate, rats climbed high into a tree. A brazen rat jumped into a bin and pulled a chunk of food from a plastic bag while I watched, less than a meter away. Mr. Donnovan believes it is nearly impossible to control an infestation of this magnitude. "There is simply too much food," he says, gesturing to bins overflowing with trash bags. "Even if we apply rodenticide, they will not eat it. They are simply uninterested. Once these bins are infested, the garbage collectors refuse to collect them either." Warmer temperatures may fuel growing rat populations, but overflowing bins, a love for fast food, and fractured communities compound the challenge. In the UK, more people are living in closer proximity. The Office for National Statistics projects the population will increase from 67.6 million in 2022 to 72.5 million by 2032, with more people residing in urban areas.
Instead of hoping poison works, the solution may be straightforward. "If we care for our city environment, then we will not have to worry about being so inhumane to them," argues Dr. Corrigan. "By denying them access to food and scraps, we do not have to poison them, kill them, or torture them." The challenge now is how to execute this quickly. After all, as Dr. Corrigan states, we have already underestimated them. "We ignored rats and allowed them to get out of hand, and now we are paying the price." Additional reporting: Florence Freeman