A data-rich look at New York’s battle against rats

The rat problem is worsening in many cities, and not just in America

For decades, New York sidewalks were awash in piled-up black plastic rubbish bags, some of which doubled as housing projects for the city’s other inhabitants. “I’ve kicked bags of garbage in New York as part of a rat safari and you just watch rats go flying,” says Kaylee Byers, an expert on urban rats at the University of British Columbia. “A rat runs across your foot. You think about it every time you’re on the block for the rest of your life,” says Joshua Goodman, a deputy commissioner of sanitation in New York. A study conducted in 2023 by MMPC, a pest-control company, suggested there were 3m rats in the city, up from 2m a decade earlier.

The externalities of supplying rats with an all-you-can-eat buffet are hard to price, but one study that attempted to do so put the damage across America at $27bn a year. (File photo of New York.) (REUTERS)

This is not only revolting. The externalities of supplying rats with an all-you-can-eat buffet are hard to price, but one study that attempted to do so put the damage across America at $27bn a year. Much of that was accounted for by rural rats nibbling crops. But city rats are more of a menace. They “urinate and defecate kind of constantly”, says Bobby Corrigan, an urban rodentologist. Rats transmit E. coli, salmonella, and more than 50 pathogens and parasites that cause diseases like typhus and leptospirosis.

The rat problem is worsening in many cities, and not just in America. This is linked to climate change, according to an analysis of 16 cities led by Jonathan Richardson, a biologist at the University of Richmond in Virginia, who has studied rat population dynamics and control for 15 years. Food abundance or scarcity affects the rate at which rats reproduce, as do milder winters. Global warming is beyond the remit of mayors, but stopping feeding time in cities is not.

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New York pioneered a misguided turn from metal containers to plastic bags after a sanitation strike in 1968. It is now leading the way back out of the rat race. Early evidence suggests that the city’s experiment with “containerisation” (or bins with lids) is tipping the scales against rattus norvegicus. While New York is winning, rat populations have been rising in Washington, DC, and Boston. That puts New York City in the unfamiliar position of being a model for the rest of America to imitate.

In May 2023 Jessica Tisch, now the NYPD’s top cop, spearheaded a strict, data-driven programme to manage and contain rubbish. Now 70% of buildings in the city—including all smaller ones and commercial premises—are obliged to use rat-resistant bins with lids. A pilot in Hamilton Heights, in West Harlem, yielded good results. A larger pilot scheme, also in West Harlem, is currently evaluating an approach for larger residential buildings to keep rats away from the remaining 30% of buildings. Reported monthly rat sightings have been dropping (see chart).

In Washington, DC, by contrast, rat complaints rose nearly 13-fold from 2014 to 2024. In Boston complaints more than doubled and in Toronto they nearly tripled, suggesting the rats are not singling out the United States for special favours. In Washington the city government does not always provide or mandate that private contractors use ratproof bins. “A lot of times people get the cheapest possible bin from Home Depot that rats can just chew right through, or leave drain holes or lids open,” says Dr Richardson, disapprovingly. In some neighbourhoods in Boston residents still put out plastic bags and rubbish can be out on the street four days a week.

“Cities have been tackling the wrong part of the problem,” says Dr Byers, the occasional kicker of rubbish bags for research purposes. Their focus has been on killing with traps and anticoagulant rodenticides (which can also kill other wildlife). Chicago is experimenting with rodent contraception. Instead of enforced family planning for the creatures, which after all have four legs and are mobile, cities would do better to just cut off their food supply. “Why eat the bait when you’ve got a piece of pizza nearby?” asks Dr Byers.

This seems obvious. Yet while New York has a “rat tsar”—or had until she resigned recently with no explanation—“a huge proportion of cities in the US don’t really have any planned response, which just leaves these massive gaps in management,” says Niamh Quinn, who specialises in interactions between man and wildlife at the University of California.

Boston is a rare other big American city that is making itself less welcoming to rodents. Rats are “one of the top concerns that we hear for quality of life across Boston”, says Michelle Wu, the mayor. The city has launched assessment programmes and installed several hundred remote sensors to track rats as they commute from home to lunch. Mayor Wu says the city plans to improve the frequency of rubbish collection and expand containerisation over the next three years. Though only after “community engagement to make sure that everybody would be on the same page”. Why wait? New York has already shown rats can be sent packing.

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