First, The Numbers: How Many Rats Are In Chicago?
There is no definitive answer to this question. By their very nature, rats are difficult to track and count. They also reproduce quickly, with a typical gestation period of only 21 days. One popular misconception is that there is one rat for every person in big cities. However, this theory was debunked decades ago.
Today, in Chicago, complaints made to the city’s 311 service offer a helpful starting point. According to city data, Chicago received about 39,000 rat complaints in 2018. Conventional wisdom among exterminators holds there are “10 rats for every rat you see,” so if you believe that ratio, Chicago could have 390,000 rats.
Chicago biologist Maureen Murray studied whether there are actually more rats in the neighborhoods with the most 311 rat complaints (or whether residents of some neighborhoods simply complain more than others). By trapping and counting rats in different neighborhoods, her team found that 311 complaints do correspond with the numbers of rats. This map shows which Chicago neighborhoods have the most rat complaints — and according to the study’s results, the most rats.
Q&A With Rat Expert Rebecca Fyffe, Director Of Research At Landmark Pest Management
Where do rats live in the city?
Since rats are a prey species, they need to stay out of sight, which is why they excavate soil and dig under cement slabs to build extensive burrow complexes. They invade our homes, garages and gardens.
What are some fun things you’ve learned about rats?
Rats demonstrate social learning [and] teach learned behaviors to other rats. Rats are also impressive athletes: They can tread water for three days [and] can flatten their bodies to squeeze through half-inch openings.
What’s the ideal number of rats in a city?
The ideal number of rats in a city is zero. Norway rats [the kind found in Chicago] reached North America around 1755 on the ships of the settlers, and they haven’t done anything beneficial since. They’re a disease risk, a fire hazard, they cause our sidewalks to collapse and they bite babies in their cribs.
What’s the impact of rats on human health?
Seoul hantavirus, hepatitis E, leptospirosis and flea-borne typhus are just some of the diseases that humans can contract from living in close proximity to rats. Because the symptoms of these pathogens in humans can resemble other common illnesses, scientists think that infection in human populations probably goes underdiagnosed.
What are the best ways to reduce rats in cities?
The only way to meaningfully control rats in the urban environment is to eliminate their access to garbage and to our structures. We need to have construction standards that seal rats out and improve our trash-handling practices to eliminate rats’ nightly buffet.
More rat tales!
We asked you to send us stories of your wildest encounters with Chicago rats — here are some of our favorites.
More about Curious City
Curious City is a show from WBEZ that answers people’s questions about Chicago and the region. You can ask questions, vote on your favorites and join reporters to track down answers. Besides zines, our stories have been told through video, audio, quizzes and even live events. Follow along on Facebook and Twitter, and check out our latest stories online or on your favorite podcast app.
More about our questioner
Justin Carrasco is a rising eighth grader at Unity Junior High School in Cicero. He became curious about rats in Chicago after reading a book about the large rat population in New York.
He sometimes spots rats in alleyways, crawling into garbage carts through small holes. One time, one got a little too close. “It ran in front of me, and I got scared,” he says.
Justin’s favorite class in school is gym, and his favorite sport is soccer. In his free time, he likes to play Grand Theft Auto V. One day, he hopes to pursue a career in mechanical engineering and build sports cars.
Illustrations by Ellie Mejía | Reporting by Jesse Dukes | Editing by Jessica Pupovac
Design and development by Katherine Nagasawa and Paula Friedrich