Gangs of Hungry, Violent Rats Take Over the Streets of U.S. Cities

Humans aren't the only ones whose lives have been disrupted by the coronavirus pandemic. Millions of rats that live below the streets of big U.S. cities have seen their world turned upside down—and the results can be violent.

When times are good, the rats inhabit subways, sewers and basements by day. They emerge mainly at night to feast on the considerable amount of food left over from restaurants – an estimated 22 billion to 33 billion pounds of food waste each year in the U.S. In a city like New York, which had about 27,000 restaurants as of 2018, that amounts to a considerable supply of food—enough to support about two million rats, the third largest rat population in the U.S. after Chicago and Los Angeles.

The March lockdown caused a major disruption in the food supply-chain for rats. No longer were restaurants tossing half-eaten hamburgers, pizza slices and sushi to the sidewalk in thin, plastic garbage bags that rats easily penetrate with incisors that have been known to gnaw through metal, concrete and brick.

For the past months, these normally cloistered creatures have been taking to the streets in broad daylight—behavior that has astonished rat experts. "We didn't realize they were so dependent on our garbage for survival," says Bobby Corrigan, an urban rodentologist and pest management consultant who designed rodent control programs for New York City's Department of Health and Mental Hygiene. "The pandemic proved just how dependent they are on us."

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Normally cloistered rats have gotten more aggressive in their search for food during the coronavirus. Sanjay Kanojia/AFP/Getty Images

In Chicago, packs of rats that don't normally travel more than 150 feet outside their burrows are venturing further to look for their next meal. In New Orleans, rats have been spotted scurrying out into the open and empty streets frantically searching for food. Midtown Manhattan, an area of New York City normally bustling with humans, is now occupied by armies of desperate rats, who run free digging through garbage bags. In May, the Centers for Disease Control and Prevention warned that rats were becoming increasingly aggressive in their hunt for food, as restaurants across the U.S. remain closed.

Rats generally live in packs of a dozen or so, led by an alpha rat that is bigger, stronger and faster than the followers. Each pack establishes territorial foraging habits that usually keep conflict to a minimum. Now that rat packs are searching far and wide for new sources of food, however, they've clashed frequently, and often violently, resorting to cannibalism and infanticide and littering the streets with dismembered corpses.

The bright side of the rat wars is that humans are not among the casualties: rats are only aggressive and violent only toward each other. "They won't come fighting our ankles or trying to attack us when we sleep," says Corrigan.

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As cities begin phased reopenings, Newsweek asked Corrigan about rat behavior and the challenges of living among them. Excerpts:

Newsweek: What is the key behavior that's changed since the pandemic started?

Corrigan: That key behavior is exposure. This is an animal that has done very well because it's an expert at being cryptic. It's the color of shadows, it uses the cloak of dark and shadows below bushes to get around. It's an expert at being secretive. This pandemic stripped that all away – food was not there at 3 o'clock in the morning anymore. It wasn't there when they could run shadow to shadow. They had to expose themselves by traveling further which they do not like to do, and they had to compete and expose themselves to their own enemy, which they do not like to do. I'd say for me, the biggest difference is that they're exposed.

How can we tell if a rat is aggressive? What kind of qualities would they display?

The press has been seizing on that word "aggressive" that the CDC released, very important. They are being seen more readily during the day and they're being seen in areas that they are not normally seen.

What should we do if we see one of these rats in our home?

So here's the interesting thing. It is so simple. When you take out your trash, put it in something that rats cannot get to. And keep whatever you put your trash into very clean with disinfectant. Get a handy person and improve the basis of your doors. There are materials you can get at Home Depot for rat proofing. So that's the easy thing for the exploratory rat. But if you develop a rat problem, like a family of rats moved into your home, that's not a do it yourself thing. That is a job for pest professionals.

From how far away can rats smell food in your car or in your home before they go in and try to explore?

Rats have a great sense of smell in general and they keep their nose to the ground. Food has very heavy molecules and settles to the ground. When someone cooks eggs for breakfast and the windows are open, those molecules are drifting out the window down. They can pick up the scent of food easily, several hundred yards away.

How hungry do they have to be to resort to cannibalism?

Pretty hungry. Small mammals with high metabolic rates like rodents and other small mammals eat on a pretty regular basis. After a couple of days of being denied food, that's when they will become aggressive with each other. If a rat is denied for a couple of days, to the point where they physiologically feel ill or sick, mammals like that will begin to attack each other. They'll begin to prey each other's nests looking for pups, and they will begin to kill those pups. And so it's only a couple of days and then they go to war, if you will, they have battles. That's what's being reported by the pest control professionals that they're out working every day. They're seeing in certain areas, these rats that have been killed by other rats.

How common is cannibalism in rats?

It's pretty common. We didn't realize how dependent rats have been on our garbage. We've known they're depending on us for food. And by being dependent on our garbage, there was no reason for many of these rats to go to these wars. Even though they still had their fights, there were still killings and cannibalism from time to time. But it's nothing really new and it's nothing new among any of the animal populations.

What does going to war with each other look like? Does that mean a stronger rat attacks a weaker rat? How does that work?

Going to war means when all that food all of a sudden has been reduced to a very low level, you will start seeing them establishing dominance. You will see them wrestling and fighting and trying to kill one another. And it actually looks to me like a single wrestling match when it's going.

What does establishing dominance mean? Is there an alpha rat that leads the pack?

In a rat litter of 8 to 10 pups, not all teets on the mother are equal. Certain pups are going to get the best milk from the best teet. They'll grow up to be the largest and most well fed they're going to bully around the smaller ones. The big rats tend to be the alpha rats and have behavioral traits that lends toward aggressive versus passivity. Put that together and you get Mr. Alpha Rat or Mrs. Alpha Rat. Though it's typically a male kind of thing. But females do fight like crazy to defend their nests.

What can we expect after the pandemic? Will we see a different type of rat population where only the dominant have survived, or is this pandemic not long enough for that to happen?

It's not long enough for that happen by a long shot. If you talk to urban evolutionists that study these kinds of things like are rats going to evolve into a more aggressive or a different kind of animal? The answer is no. These animals are so successful for a lot of reasons, but one of the main reasons they're so successful is high resiliency, the most resilient of animal population.

As cities open up, how will rats change their behavior?

Their migration patterns are a block by block situation. The rats that were most affected by the restaurants closed in the city travel as far as they need to, to find another source if they could.

And if they couldn't, that's when they start killing each other and going to war. We will never know what percent of those that were most effected died. We'll never know what percent of those successfully migrated to another area and survived. We are never going to know any of that, but in general, these animals generally tend to stay within about 500 feet radius of their nest. That's their typical home range. Now when that's disturbed they'll travel several blocks.

Several blocks?

When [scientists] put radio tags on these animals in England, in 24 hours [one rat] went five miles round trip from its nest and came back to the same exact nest. So when they have to, they're tremendous dispersers, and that is evidenced by the fact that they're all over the world.

Will these rats return to business as usual after the pandemic?

I'm not sure. We're living through somewhat of a wide experiment that nobody designed or anticipated. We'll know when the rats are back but we won't know if it's the same rats. We're probably never going to know that. We'd had to have tagged these rats with numbers but we didn't do that.

What does the media currently get wrong about rats?

The press loves to paint rats as these scary demonized animals that are out to get us. Hollywood does same thing. We Hollywoodize this animal with fear. A lot of times when I give [interviews], the story is right but the editor puts a headline on it that's like "big, aggressive, giant rats seen in Washington D.C." I don't know where they come up with those headlines just to get readers eyes on it.

Gangs of Hungry, Violent Rats Take Over the Streets of U.S. Cities | Tech & Science