Rats Aren’t Nearly As Populous As We’re Led To Believe

By Debra Kelly on Thursday, February 19, 2015
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“Come out and take it, ya dirty, yella-bellied rat, or I’ll give it to ya through the door!”” —Jimmy Cagney, Taxi! (1932)

In A Nutshell

Listen to the popular horror stories about just how many rats there are in the world’s cities, and it’ll make you not want to go there. From being just a few steps from a rat no matter where you are to being outnumbered by them at least two to one, the popular stories are greatly, greatly exaggerated. While rat populations are still in the millions, they’re also not at the point where you need to worry about them flooding out of the toilet, either.

The Whole Bushel

There’s a whole bunch of folklore that talks about how humans are way, way outnumbered by rats. According to some, there are twice as many rats as there are humans living in cities like New York and London, and the other statistics you’ve probably heard include things like, “You’re never more than 6 feet from a rat.”

You’ve probably heard horror stories about rats living in the sewers and swimming up through drains when there are too many of them, emerging from toilets and drains in the streets.

The good news is that stories of rat populations are less horror stories than they are urban legends, and we’re pretty sure we know where the stories come from.

Cities have rat populations, that’s not argued. But less-than-trustworthy (read: outright lying) news sources like the Daily Mail and the New York Post even now issue warning articles that state the rat population has risen to double that of New York City’s human population (that makes about 17 million rats), while if you believe the Daily Mail, super-intelligent, giant rats are now on their way to taking over not only the native rat population, but invading human territory, too.

Other researchers, with data based more on scientific fact, aren’t nearly as apocalyptic in their estimates.

Statisticians from the Royal Statistical Society looked at just what the realistic estimates for a rat population are. They started with basing the data on factors like the number of rat sightings in different areas of New York City; that gave a starting point for the number of places that there actually are rats in the city. Looking at the numbers, there are only about two million rats in the entire city.

A lot, sure, but that’s nothing compared to the stories of two rats per person.

Similarly, professors from the University of Hudderfield ran the numbers for England. They based their estimates on a pretty diverse amount of factors, like how many homes have reported having rats (less than half a percent), how many have rats outside (only about 3 percent), and how many commercial and industrial lots there are that have reported rats.

Estimates suggest the entirety of the UK only has about 10.5 million rats, and that means that you’re not even close to being only 2 meters (6 ft) away from a rat no matter where you are. On average, that’s more like 50 meters (165 ft), although admittedly the population is far from evenly distributed.

So where do we get the idea of the terrifying numbers of rats that we share our cities with?

One of the earliest sources for assigning numbers to the rat population comes from a 1909 book called The Rat Problem. Written by an Englishman whose scientific method for determining whether or not there were rats around was asking people if they’d seen any, he estimated that there was about one rat per acre living in the English countryside. That meant that there were 40 million rats living on 40 million acres. This matched nicely with the human population of the time, which was also about 40 million.

The numbers were convenient and easy to remember, and they stuck.

Show Me The Proof

BBC News: Are you never more than 6ft away from a rat?
NPR: Rats! New York City’s Population Might Be Seriously Overestimated
New York Post: There are twice as many rats as people in NYC
Daily Mail: Swarm of ‘super rats’ spotted across the country ‘expected to outnumber humans two to one by next year’