“In truth, the city’s rat population is probably closer to 2 million,” said Mr Auerbach, a Columbia Ph.D. student who conducted a study on the topic.

“The urban lore that there are as many rats as citizens dates back at least a century.”

“It may have endured in part because reliably estimating the city’s rat population is difficult even though the creatures are hardly invisible, as most New Yorkers who see them skittering about the subway tracks or hear them rustling through trash piles will attest.”

Mr Auerbach’s initial plan was to use a method that involves capturing a random sample of rats, marking them, releasing them, and then capturing another random sample of rats. But the New York City Department of Health and Mental Hygiene was not enthralled with the idea.

Instead, the scientist used complaints from the public about rat sightings, which the city tracks and publishes online.

Combining the data with a number of assumptions, Mr Auerbach was able to extrapolate the number of rat-occupied lots to about 40,500 across the city, or less than 5 percent of the total.

If each inhabited lot is home to a typical colony of 50 rats that would mean there are about 2 million rats in the New York City.