This is what happens to all rats when cities flood

(CNN) – In the aftermath of Hurricane Ida, torrential rains that hit cities across the East Coast in early September overflowed storm drains, poured into subway stations and filled basements like bathtubs. The devastating number of human victims is well known. But less clear is what happened to the inhabitants of the subterranean depths of those cities: the rats.

It is impossible to know how many rats are in a city – probably in the millions – or how many were lost during a major storm.

Experts agree that, where Ida dropped record rains, many rats that lived in the sewers would surely have died from the sudden flood. In New York City, on September 1 it rained 80 millimeters in a single hour, about 10 millimeters less than the normal monthly total.

Perhaps hundreds of thousands of rats were crushed or drowned by the flood, Bobby Corrigan, a leading rat expert and former rodentologist with the New York City Department of Health and Mental Hygiene, told Gothamist. Dead rats have been seen on the city’s beaches.

The New York City health department knows that some rats drown in severe flooding, but since the city does not conduct rat censuses, there is no data on how many, said spokesman Michael Lanza.

In addition, the department uses rat sighting reports and inspection reports to track rodent activity. So far, the reports have not increased since the Ida pass. The same is true in Philadelphia, which was also devastated by the rains, according to officials from that city’s health department.

But the rising waters are not enough to wipe out these intrepid members of a city’s Rodentia. Rats are excellent swimmers, says Michael Parsons, an environmental biologist and visiting researcher at Fordham University in New York. They can swim 0.5 miles or more and stay in the water for three days in a row. (They can even swim to the toilet.)

And rats are cunning, apt to move to higher ground if they get the chance.

“To put it scientifically, rats are not stupid,” says entomologist Michael Waldvogel, an emeritus professor of extension at North Carolina State University and an expert on “anything people find disgusting and disgusting.”

“They are going to get to where they are out of harm’s way,” Waldvogel said. “And if they have to, they will keep going up.”

The Norwegian rat, the most abundant species in New York City, makes its home in sewers, sidewalks, and underground burrows. But this animal can climb vertically. And once you enter a building, you can chew between the walls and climb them. The smallest black rat is arboreal, that is, it lives in trees, and naturally heads upward. This urban dweller is common in New Orleans, where it is aptly known as the roof rat.

Even if a catastrophic flood caught and killed many rats underground, many more would find their way to safety.

After the flood

Considering how these animals respond to shocks, Parsons predicts that the rats would not only survive Ida, they could thrive. During the pandemic, according to his early research, New York City rat populations adapted to changes in their normal food resources that resulted from restaurant closings during the height of physical distancing. “The weakest or most unlucky rats died, while the most fortunate or resistant individuals found ways to survive,” he said.

The survivors reproduce, quickly and frequently. According to Waldvogel, twenty rats can easily turn into several hundred in six months.

“It’s kind of a counterintuition,” said Michael Blum, a professor in the department of Ecology and Evolutionary Biology at the University of Tennessee in Knoxville. “You think that, in these flood-affected areas, these animals should disappear. But in reality, things disappear, but they reappear very quickly. They can become much more abundant than they were before the flood.” .

Blum studied the impact of Hurricane Katrina on rats in New Orleans. Their research, published in August, found that, 12 years after the historic 2005 storm, rats were thriving in heavily flood-damaged areas, where many buildings had been left empty.

Rodent populations were even higher in underserved, often predominantly black neighborhoods, such as the Lower Ninth Ward, where vacant lots were not well preserved.

In fact, what happens to a city’s rodent population after a major flood is largely determined by human response once the waters recede.

“In the case of Hurricane Katrina, the infrastructure was so damaged that trash and everything on the street took a long time to be collected,” said Claudia Riegel, director of the New Orleans Mosquito, Termite and Rodent Control Board.

Empty refrigerators and debris from damaged houses remained in the streets, providing food and resources for the rats and forcing the board to mount a large control effort, including placing rodenticide in storm drains where rats congregated. . “We tried to prevent the population from increasing exponentially,” he said.

Public health measures are needed

This has important public health implications, as rats carry dozens of pathogens, including salmonella and the bacteria Leptospira, which cause leptospirosis. The infection can cause fever, chills, and vomiting within days of exposure, and can lead to kidney or liver failure.

“If you see a rat, you have to assume it has some kind of pathogen,” Reigel said.

Flood waters can become contaminated with the urine of rats, which can increase the risk of leptospirosis. (Michael Lanza noted that the disease is rare in New York City and there are no known cases associated with this or previous floods.)

To maintain rat populations and prevent disease transmission, it is vital that storm cleanup is done as quickly as possible. Damaged properties must also be maintained in the following months and years. As Blum’s research showed, simply cleaning empty lots can go a long way in controlling rats.

The same principles apply in the absence of weather events, Reigel stressed. Covering garbage cans, not feeding the birds, and picking up dog poop (rats eat it) are all measures that help keep rat numbers under control. Because if there is a place to dig and something to eat, rodents are likely to take advantage of it.

In short, “says Waldvogel:” The rats will survive. “

Amanda Schupak is a science and health journalist in New York.