How New York got rid of its rat problem – and why it won’t work in the UK

Reports from New York this week have revealed that the city’s pest controllers have been deploying a new weapon in the war on rats. They’ve been blasting the rodents’ burrows with carbon monoxide gas for what sounds like a double win: the swift and painless extermination of creatures that cause terrible damage to property and spread potentially deadly diseases. So if it’s working there, can it work in the UK? 

Although British cities aren’t as plagued with rats as the Big Apple, our problem is escalating. We now have an estimated 200 million brown rats living in our urban areas. According to a survey by insurer Direct Line, local authorities across the nation spent around £36m to control 225,430 residential rodent infestations in 2022 – equivalent to 618 per day. 

“The brown rat population in the UK has increased by around 6.4 per cent since 2020,” says Paul Blackhurst, Technical Academy head at Rentokil Pest Control. But while he says he’s been interested to read about the “good results” reported by his American colleagues, he suspects carbon monoxide won’t solve Britain’s escalating rat problem. 

“Carbon monoxide is a very dangerous gas,” he says. “It’s dangerous to humans. Although it will kill rats very very well, in the UK we’d be really limited as to how and where we’d ever be able to use it without having to evacuate areas.”

Blackhurst understands that New York exterminators are using the gas “in areas that are planted with trees, in raised flower beds in the streets”. In such places, rat burrows could be shallow, so any gas would disperse gradually into the atmosphere. “But if those burrows reach down into drains,” Blackhurst says “you’d have to worry about where that gas is going.” 

He explains that British pest controllers are already permitted to use a similar gas: aluminium phosphide. But because it’s so toxic, it’s strictly regulated. “We can’t use it within 25 metres of an occupied building or 10 metres of a water course,” explains Blackhurst. “We can’t use it on rainy, foggy or snowy days. It controls rodents very rapidly. But we would very rarely deploy a gas that would kill anything – certainly any mammal – that comes into contact with it. I think we’d end up having the same problem with carbon monoxide.” 

By contrast, Blackhurst says that the traditional anticoagulant rat poisons authorised as humane and licensed for use in the UK are “relatively safe to use around humans. You’d have to eat a lot of them to cause a serious problem. The same goes for dogs; large dogs would certainly have to eat a lot although obviously smaller dogs would need to ingest less. But there are environmental concerns and, for pest controllers,  it’s a case of selecting the right method on a case by case basis.” 

Blackhurst says his colleagues at Rentokil, like many in the industry, are trying to reduce their rodenticide use and go down a more sustainable route. 

“The carbon emissions of a gas like carbon monoxide mean that – even if the gas were authorised for use here – using it would still be up for serious debate.” 

Instead, Blackhurst argues that “prevention is always preferable to cure”. Having opened bins filled with over 50 rats, jumping out and running over his feet, he says our national waste management needs to get much better. “The rising cost [of rubbish collection] has become so prohibitive that waste hangs around for far too long and rats will take advantage of that. We need good waste management and good rodent-proofing of buildings, making sure they’re sealed as well as possible.” 

Blackhurst has an admiration for his long-tailed foes. “They’re a lot like humans,” he says. “They’re very intelligent, tough and adaptable. All they want is food, water and somewhere safe to live. And we’ve created conditions that offer them all of that – we’ve given it to them on a plate. In return, they cause a health risk, and a fire risk when they chew through cables.”

Although British newspapers were full of reports of cat-sized, poison-resistant “super rats” earlier this year, Blackhurst doesn’t like the term. “Are they getting bigger? Possibly. When they have access to protein-rich food then they may be bigger. We also know that, in large swathes of the country, some rats have become resistant to poison due to a genetic mutation. Those rats are now breeding all the way through from London to Berkshire and a female rat can have six or seven litters in a year.”

But instead of poisoning them, Blackhurst believes we need to stop providing them with an environment that enables them to multiply. “We need to change our lifestyles. Improve our hygiene. We need to seal our homes and offices, because they get in through lofts, gaps in walls, and pipes. Rats are very good climbers.” 

He’s a fan of the ‘rat flaps’ that prevent the rodents from climbing up pipes into our sinks and toilets. (Essentially, they’re a non-return valve.) “Our sewers are all shapes and sizes in the UK and I’ve seen builders put extensions on houses and use supermarket carrier bags to block off the main sewers. That’s no deterrent. Rats can tread water for three days. But I’ve seen long term infestations halted overnight by rat flaps.”