That happens to all rats when cities flood

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Posted by Amanda Schupak, CNN

After Hurricane Ida, the pounding rain that hit cities along the east coast in early September flooded gullies, poured into subway stations, and filled basements like bathtubs. The devastating human death is known. It is less clear what happened to the inhabitants of the underground depths of these cities: the rats.

It’s impossible to know how many rats are in a city – probably on the order of millions – or how many were lost in a major storm. Experts agree that where Ida dropped record-breaking rainfall, many rats living in storm sewers would certainly have been killed by the sudden flood. New York City fell eight centimeters of rain in a single hour on September 1st – about an inch less than the normal monthly total. Perhaps hundreds of thousands of rats were crushed or drowned in the Flood, Bobby Corrigan, a senior rat expert and former rodent scientist for the New York Department of Health and Mental Health, told Gothamist. Dead rats have been spotted on city beaches.

The New York City Health Department knows that some rats drown in severe floods, but since the city does not keep rat counts there is no data on how many, spokesman Michael Lanza said. The department uses rat sightings complaints and inspection reports to track rodent activity. So far the reports have not increased since Ida’s transit. The same applies to Philadelphia, which was also devastated by the rain, according to the local health authorities.

But rising water alone is not enough to bring down these sinister members of a city’s Rodentia. Rats are excellent swimmers, says Michael Parsons, environmental biologist and visiting scholar at Fordham University in New York City. You can swim half a mile or more and tread water for three days. (They can even swim up your toilet.)

And rats are smart and have a tendency to move to higher elevations when they can.

“To put it scientifically, rats aren’t stupid,” said entomologist Michael Waldvogel, North Carolina State University Associate Professor Emeritus and an expert on “everything people find gross and gross.”

“They will arrive where they are out of danger,” said Waldvogel. “And if need be, they’ll keep going up.”

The Norway rat, a common species in New York City, is at home in sewers, sidewalks, and underground burrows. But this living being can climb vertically. And once it gets inside a building, it can chew on the walls and climb them. The smaller black rat that lives on trees, which means that it lives in trees, naturally goes up. This city dweller is common in New Orleans, where he is aptly known as the roof rat.

Even if catastrophic floods captured and killed many rats underground, many more would likely find their way to safety.

After the flood

Given how these animals are known to respond to crises, Parsons predicts that rats Ida would not only survive but thrive as well. During the pandemic, according to his early research, rat populations in New York City adapted to changes in their normal food resources that resulted from restaurant closings at the height of social distancing. “The weaker or unhappy rats died while the happier or more resilient individuals found ways to survive,” he said.

The survivors multiply – quickly and often. Twenty rats could easily become a few hundred within six months, Waldvogel said.

“It’s kind of counter-intuitive,” said Michael Blum, a professor in the Department of Ecology and Evolutionary Biology at the University of Tennessee, Knoxville. “They think in these flood-hit areas these things should be erased. But really, things get wiped out, but they come back very quickly. They can occur much more frequently than before the flood. “

Blum studied the effects of Hurricane Katrina on rats in New Orleans. His research, published in August, found that 12 years after the historic 2005 storm, rats thrived in areas that had been badly damaged by flooding and where many buildings were vacant. Rodent populations were even larger in underserved, often mostly black, neighborhoods like Lower Ninth Ward, where vacant lots were not well maintained.

Indeed, what happens to a city’s rodent population after a major flood is largely determined by the human response when the water recedes.

“In the case of Hurricane Katrina, the infrastructure was so badly damaged that it took a long time to pick up trash and everything that was left on the roadside,” says Claudia Riegel, director of the New Orleans Mosquito, Termite and Rodent Control Board. Empty refrigerators and debris from damaged houses remained on the streets, providing food and resources for rats, and required extensive control measures from the board, including putting rodenticides in rain drains where rats would congregate. “We tried to keep the population from actually growing exponentially,” she said.

Public health action is needed

This has important public health implications as rats carry dozens of pathogens, including salmonella and the bacterium Leptospira, which causes leptospirosis. Infection can cause fever, chills, and vomiting, and kidney or liver failure, within a few days of exposure.

“If you see a rat, assume that it has a pathogen,” said Reigel.

Floods can be contaminated with urine from rats, which can increase the risk of leptospirosis. (Lanza noted that the disease is rare in New York City and there are no known cases related to this or previous floods.)

To keep rat populations low and prevent disease transmission, it is important that storm clearing occurs as soon as possible. Damaged objects must also be cared for in the months and years that follow. As Blum’s research has shown, simply mowing vacant lots can go a long way in controlling rats.

The same principles also apply in the absence of a weather event, emphasized Reigel. Putting lids on trash cans, not feeding birds, and picking up your dog’s feces (rats will eat him) all of these will help keep rat numbers under control. Because if there is a place to dig and something to eat, the rodents will likely benefit.

“The bottom line,” said Waldvogel: “Rats will survive.”

The CNN Wire
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Amanda Schupak is a science and health writer based in New York City.

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