As a graduate student at Purdue University about two decades ago, Bobby Corrigan spent weekends living inside a commercial granary in Indiana. As part of his doctoral thesis, he observed how rats live, behave, and reproduce, following about 10 separate rat families on several floors of the sprawling facility. The population stood at about 150 rats, all told.
After a few months, Corrigan decided to remove their food supply by meticulously cleaning up all the loose grain.
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At first, there were loud squabbles and fighting among the rodents. Over the next several nights, that progressed to outright battles and even cannibalism. In a few days, nearly all of the rats on the property had disappeared. They had either moved to a small town nearby or died before they got the chance.
Corrigan, a consultant and urban rat ecologist, now lives in New York City where he advises city officials, airport staffers and pest control companies on how to handle their rat problems. He says that since the pandemic hit, cities across the country have been witnessing a replay of his Indiana granary experiment. Urban rats that had been feasting on restaurant dumpsters and back-alley garbage cans for their entire lives have seen their food sources disappear. As a result, they are changing their behavior: foraging during the day, sleeping in cars (they chew on the wires, mistaking them for edible roots), invading apartment buildings, and—just like in that granary—practicing rat-on-rat cannibalism, known as muricide.
“These animals become aggressive when they are starved,” Corrigan says. “They are attacking each other. It’s pretty gross, but it’s life in the wild.”
This stressed-out rat behavior has been reported in Chicago, where pest control experts are reporting cannibalism and other unusual behaviors; in the New Orleans tourist quarter of Bourbon Street; and in Philadelphia, where a pest control expert found one home infested with 20 rats that had moved in after losing their food from local restaurants.
Rats usually live together in underground colonies located about 50 to 75 feet from a food source. But as food has become more scarce, the range that each rat travels has gotten larger.
Rodent control teams are reporting a big shift as rats expand their range to look for food, according to Jim Fredericks, chief entomologist for the National Pest Management Association.
“We don’t have any data that rat populations are increasing,” says Fredericks. “What we are seeing is some observations of rats behaving in ways they normally do not. Primarily, they are acting in a brazen way, during the day, in places where they had not been seen before. I suspect it has a lot to do with how humans are behaving. These urban centers that would be bustling with people are now ghost towns.”
Urban parks, tourist areas and restaurant rows that are normally packed with people munching on food are now nearly empty because of coronavirus lockdown measures. Fewer people equals less food for rats. And even out in the suburbs, Fredericks says, according to members of his organization, hungry rats are abandoning strip malls to invade nearby homes in search of food.
Scarcity has also created conflicts within each colony, he says. “Usually there is an alpha rat that gets first dibs on food before the others,” Fredericks says. “A young juvenile has to wait, and so that competition increases. With more rats vying or less food, tensions rise and there is the potential for these rats becoming violent with each other.”
While rats don’t transmit the coronavirus, they can be carriers of other diseases such as salmonella or leptospirosis, Fredericks says. These are among many diseases that rats spread directly to humans through infected urine or droppings, or indirectly by carrying ticks or fleas that then bite humans and transmit the disease.
If you do find a rat in your neighborhood, the best way to deal with it is to remove outdoor food sources and block entrances to your home or apartment building. That means sealing up any openings the size of a quarter, or any half-inch doorway gap. You will also have to enlist your neighbors. Just as the novel coronavirus can spread through a restaurant or crowded market, so, too, can rats infest a neighborhood where not everyone is doing the right thing to eliminate food waste and clean up their garbage.
“Our weak link is that not all of us behave correctly,” says Corrigan. “It only takes one of 10 misbehaving humans to give the rats what they need. The problem is: How do you get 100 percent of your neighbors to behave correctly? It’s very hard to do.”
Corrigan notes that rats aren’t confined to low-income areas of a city. “If you have a wealthy person that lives like a slob, they will cause problems for the entire complex,” he says.
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One urban rat expert is using the global Covid-19 lockdown to study how rat behavior is adapting to changes in human behavior. Michael Parsons, a visiting scholar at Fordham University in the Bronx, is collecting data for a global research project using data from pest control companies and city officials in several countries. Parsons says that the coronavirus lockdowns that are forcing the movement of rats from one neighborhood to another—or from urban centers to suburban zones—are an opportunity to collect new data on rat behavior.
“Mass migrations of rats don’t come along very often, so our intentions are to document as many global events as we can with help from industry,” Parsons wrote in an email to WIRED.
Parsons isn’t sure if there are more rats out there during the pandemic, or if it’s just that people are noticing them more, and of course, posting images on social media, which reinforces the belief that more rats are around.
One glum note: As life begins to return to normal in some areas, Parsons believes rat populations in urban areas will rebound, just as they have throughout history. “Once restaurants are open,” Parsons wrote, “you then could have rats in both the new and the old places.”
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