Rats and people have a close relationship—whether people like it or not! Rats follow people because they like eating people’s food. (One study showed that rats in cities have three favorite foods: macaroni and cheese, scrambled eggs, and cooked corn.) Many people don’t consider rats good company, and think of them as dirty animals that spread diseases. And it’s true that rats don’t benefit people much—unless you count “cleaning up” their garbage. (Rats do eat garbage. But they may rip apart your trash bags to do it.)

Gerard Brown is the head of the city’s rodent control department in Washington, D.C. He says a string of gentle winters has made rats able to breed constantly. The harsh winters don’t necessarily kill off the rats. Most Norway rats live only about eight months, and they stay warm by burrowing underground or chewing their way into basements. But a long freeze would choke off their food supply. Less food means fewer babies are born. And a mature female rat can give birth to one litter per month, with an average of 10 babies per litter!

The city’s human population is growing too. More than 700,000 people live in Washington, D.C. That’s more people than live in some whole states! “More people with more money means more restaurants, which means more garbage, which means more rat food,” Mr. Brown says. Rats are having trash-eating parties all night! And they are hard to get rid of. A rat can fall 50 feet and not get hurt. It can even survive being flushed down a toilet by treading water.

God has given officials a responsibility to keep cities clean. But what can be done about the rats? One rodent scientist has an idea: Collect trash at night instead of early in the morning. But city-dwellers probably won’t go for that. Garbage collectors don’t want to work at night. And others don’t want to hear noisy garbage trucks while they’re trying to fall asleep. “Too bad,” some experts say. “It’s that or the rats!”