Rats have lived alongside city dwellers for centuries. Usually, their presence is unwanted, with the occasional exception of certain creatures who seem particularly endearing (remember New York City’s “Pizza Rat,” who shot to social media fame in 2015?). Usually, however, they are reviled as unhygienic disease carriers, and there’s certainly some truth behind their bad reputation. Aside from that, they are also known to damage infrastructure, contaminate food, and chew through wires, sometimes sparking fires. They can also cause serious mental health problems for people who live with rat infestations.
Yet despite countless efforts to bring rat populations under control, new research suggests that in many cities, the opposite is happening.
Intrigued by anecdotal reports of rats “taking over” various urban areas, biology professor Jonathan Richardson of the University of Richmond examined data on rat sightings, trappings, and inspections from 13 major U.S. cities, along with Tokyo, Amsterdam, and Toronto, to see how their rat populations changed over a 12-year period. In 11 of those 16 cities, rat sightings increased significantly.
The study attributed this to several factors, though one stood out: rising temperatures. During mild winters, rats and other small mammals spend longer outside foraging, making nests, and reproducing. Warmer average temperatures also give them better access to food and vegetation for hiding. They are even able to detect scents from farther away.
Although rats will probably always live in our cities, there are ways to limit their presence besides simply waiting for cold weather. In addition to climate change, human population growth and urbanization also feed into burgeoning rat numbers. Yet many vermin-control efforts are underfunded and focus on extermination rather than the underlying cause of the infestations, such as the presence of garbage and food waste on city streets.
A very ratty problem:
- Have you ever heard the saying that you are never more than six feet away from a rat in a big city? It’s a myth—at least for now.
- The cities that saw the biggest increases in their rat populations were Washington, DC, New York City, Toronto, San Francisco, and Amsterdam. Only three cities in the study experienced rat population decreases: Tokyo, New Orleans, and Louisville.
- Of the cities included in the study, Washington, DC, was the most badly affected, despite city pest control efforts such as liquid birth control. Resident complaints about rats rose from 1,448 in 2010 to 12,209 in 2021. However, there are issues with using rat sightings and complaints as a proxy for the size of the rat population, due to the rodents’ secretive nature and the fact that people who regularly encounter rats are often less likely to report or complain about it.
- Every year, rats in the United States cause damage worth an estimated $27 billion.
