Surprising Science: Rattiest City?

Orkin, the national pest control company, recently named Chicago “rattiest city” for the eighth year in a row. The company said it ranked metro regions based on the number of new rodent treatments that took place between September 1, 2021-August 31, 2022 at both residential and commercial treatments.

However, scientists at Lincoln Park Zoo’s Urban Wildlife Institute (UWI) don’t think this rating tells the whole story. In fact, they believe this rating says more about people’s attitudes toward reporting rats than it does how many rats are currently plaguing the city of Chicago.

Map of complaints about rats in Chicago over the past year.

More Rat Reports May Be Good News

Given that, more rat reports might be a positive development. Maureen Murray, Ph.D., says, “Since Chicago is a large city, it is not surprising the pest control services are routinely requested, but it is nice to see that residents are reporting their rat sightings.”

More reporting of rats may more clearly signify that people believe something can be done about the problem. This implies a level of optimism regarding city and government services, and can be encouraging in cities where rats tend to congregate everywhere in large numbers and cause public health issues. “People are more likely to complain when they have faith the city is going to do something about it,” Murray points out, adding that there is still progress to be made in getting residents to actually go through with their reports, since only about 36 percent actually do so.

And UWI has additional information Orkin might be interested in as that company looks to position itself as an industry leader. “Our research has shown rat complaints are not evenly distributed across the city but spike in areas with potential rat attractants such as restaurants, older buildings, and construction but also where there are more people to make complaints,” Murray explains. “We also suspect that Chicago’s alleys may play a role in the number of reported rat sightings as parking spaces and alleys are often an extension of the homeowner’s property versus rats seen on public streets.”

Rat sighting on a camera trap in Uptown. Photo courtesy of Deirdre McGovern.

The Chicago Rat Project

UWI started the Chicago Rat Project in 2018, with the goal of learning more about rat populations. At the time, little was known about how rats operate in cities—except that it is much harder to coexist with them than with many other kinds of wildlife. They are an invasive species, for one thing, and they carry disease and other pathogens.

The project studies the ecology and health of Chicago’s rats to help prevent human-wildlife conflict and public health risks from rat infestations. A better understanding of urban rat ecology helps prevent the risks associated with rats. “Rats are fascinating because they are arguably the most successful urban wildlife species in the world,” Murray says. “And humans are a very important part of the rat story; they’re so successful in cities because of us.”

Rat sign in an alley. Photo courtesy of Maureen Murray.

Myth Busting

Among the results of the study, UWI scientists have discovered that most people living with rats in the area are concerned with diseases like rabies, which is not known to be carried by rats, rather than the transmission of more common pathogens that are present in rat feces and urine. These include salmonella and e. coli and the bacteria that causes leptospirosis, along with viruses such as hantavirus. Thus, they may be focusing on the wrong kinds of dangers and unknowingly exposing themselves to disease.

UWI researchers have confirmed that people in lower-income areas do see more signs of rats and experience more of that exposure than people in higher-income areas—but while this isn’t surprising, it’s also not the whole story. The science suggests, as Murray puts it, “You shouldn’t make assumptions about which neighborhoods are vulnerable.” Instead, a more direct correlation can be made that rats prefer areas that have uncontained garbage and lots of food waste, even in wealthy areas. Additionally, rats were more likely to carry certain dangerous bacteria in areas of standing water.

As such, sanitation measures are key in preventing rats from congregating near urban homes. Lincoln Park Zoo is currently working with Chicago aldermen to mitigate the rat problem in the city, since rats in this city are managed at the ward level. It is also expanding the Chicago Rat Project to develop educational materials that can help citizens learn vital, correct information about these issues surrounding rats and how residents can deal with them.

Among UWI’s recommendations? “The best way to prevent unwanted rats near your home is to stash your trash,” says Murray. “Secure trash in closed bins and replace damaged trash containers.”