How rats survive major floods and hurricanes

It’s impossible to know how many rats are in a city – probably in the 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 surely have been killed by the sudden flooding. At New York, 3.2 inches (8 centimeters) of rain fell in a single hour on September 1, about an inch less than the normal monthly total. Perhaps hundreds of thousands of rats were run over or drowned in the flood, Bobby Corrigan, a leading rat expert and former rodent with the city’s Department of Health and Mental Hygiene, told Gothamist. from New York. Dead rats have been spotted stranded on the city’s beaches.

But rising waters alone aren’t enough to bring down those rough members of one town’s Rodentia. Rats are excellent swimmers, points out Michael Parsons, environmental biologist and visiting researcher at Fordham University in New York. They can swim half a mile (0.8 kilometers) or more and swim in water for three days in a row. (They can even swim to your toilet.)

“To put it scientifically, rats aren’t stupid,” said entomologist Michael Waldvogel, associate professor of extension emeritus at North Carolina State University and an expert on “everything people find gross and disgusting.”

“They are going to get to where they are out of danger,” said Waldvogel. “And if they have to, they will continue to climb higher.”

The Norway rat, the species abundant in New York City, has made its home in sewers, sidewalks and underground burrows. But this bug can climb vertically. And once he enters a building, he can chew on walls and climb them. The smaller black rat, which is arboreal, meaning it lives in trees, naturally walks upwards. This city dweller is common in New Orleans, where he is rightly known as a black rat.

Even if catastrophic flooding were to trap and kill many rats underground, many more would likely find their way to safety.

After the flood

Given how these animals are known to respond to seizures, Parsons predicted that the rats would not only survive Ida, but thrive. During the pandemic, its initial research found that rat populations in New York City adapted to changes in their normal food resources resulting from restaurant closings at the height of social distancing. “The weaker or the more unlucky rats died, while the luckier or more resilient individuals found ways to survive,” he said.

Survivors reproduce – quickly and often. Twenty rats could easily grow into a few hundred in six months, Waldvogel said.

“It’s kind of counterintuitive,” said Michael Blum, a professor in the department of ecology and evolutionary biology at the University of Tennessee, Knoxville. “You think in those areas affected by the floods, these things should be eliminated. But in reality, things are wiped out, but they come back very quickly. They can become much more abundant than they were before the floods. ”

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

“In the case of Hurricane Katrina, the infrastructure was so badly damaged that it took a long time for the garbage and everything that had been left curbside to be picked up,” said Claudia Riegel, Director of the New Orleans Mosquito, Termite and Rodent Control Board. Emptied refrigerators and debris from damaged homes remained on the streets, providing food and resources for the rats and forcing the council to deploy a major control effort, including putting rodenticides in the storm sewers where the rats congregated. “We were trying to keep the population from growing exponentially,” she 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 causes leptospirosis. The infection can cause fever, chills and vomiting a few days after exposure and can lead to kidney or liver failure.

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

Flood water can be contaminated with rat urine, which can increase the risk of leptospirosis. (Lanza noted that the disease is rare in New York City and that there are no known cases associated with this or previous flooding.)

To reduce rat populations and prevent disease transmission, it is essential that storm cleanup is done as quickly as possible. Damaged properties must also be maintained in the months and years that follow. As Blum’s research has shown, just mowing wasteland can go a long way in controlling rats.

The same principles apply in the absence of a meteorological event, Reigel stressed. Putting lids on garbage cans, not feeding birds, and scooping up your dog’s poop (rats eat it) help control rat numbers. Because if there is a place to dig and something to eat, rodents are likely to take advantage.

“Ultimately,” said Waldvogel: “The rats will survive.”