As New York City continues its phased re-opening, more New Yorkers have been out in the streets and returning to their favorite restaurants (for outside dining only). That means more garbage—and more garbage means rats can return to their normal routine of coming out at night to dine on our refuse.
Dr. Bobby Corrigan is an urban rodentologist. At the height of the pandemic in New York City, he got numerous calls from friends who wanted to tell him about this weird thing they saw a rat doing.
“You wouldn't believe what’s going on outside my condominium, it’s kind of crazy I hear screaming rats down in the street,” Corrigan recounted. He described one phone call saying: “I’m watching rats, I never seen them play in the park before, they’re wrestling, they’re playing it looks like they’re happy.’ I said, trust me, they’re not playing, somebody is going to be killed shortly and eaten!”
Corrigan is a consultant who has worked with cities on rat management all over the country, including here in New York City where he lives. And for him and other scientists who study rats, behavior like this is nothing new. Fighting and infanticide are just a few normal responses to a food shortage.
“It’s Biology 101,” Corrigan said. “Any mammals, if you take the food away you’re going to have abnormal behavior show up really quick.”
Jason Munshi-South teaches evolutionary biology to freshmen at Fordham University. He said one fact about rats is key to understanding their behavior: they’re homebodies.
“Urban rats actually use only a very small area around where they were born throughout their lifetime, think one city block.”
And they live right by their food supply, which here in the city is an all-you-can-eat garbage buffet.
“Think about a block with a lot of restaurants,” Munshi-South said. ”There would have been trash on the street nearly every night, it would have been basically predictable.”
“They absolutely know when garbage day is for their local colony,” added Corrigan.
But when the pandemic hit, the regular supply of garbage that rats rely on for food in certain neighborhoods slowed to a trickle almost overnight. A block with a lot of restaurants and a lot of garbage might support a huge colony of rats. Now those rats need to seek out food elsewhere. And rats are territorial, so with large numbers on the move, conflicts with other colonies are inevitable.
The Department of Health and Human Hygiene said the number of 311 calls about rats dropped significantly this March, April, and May compared to last year. The decline in complaints may be because people have been staying in more and therefore spotting fewer rats.
But Corrigan has another idea. The rats may have gone underground. “Some of them may have only dropped down to the sewer. A lot of food floats by in the sewers, a lot of people flush things down the toilet, smelly fish pieces and parts of vegetables, even feces.”
Munshi-South suggested that the lockdown could have caused an overall drop in the rat population. “I think that depends on how long this goes on, but I think it has already gone on long enough that there may have been a decrease. You know rats can respond really quickly to food supply so if there’s less food they’re not going to reproduce as much.”
But by the same logic, as restaurants open up again and the amount of garbage in certain neighborhoods increases, the rats’ numbers will ramp up.
“They have evolved to turn food into babies very rapidly,” said Munshi-South. “So gestation is about 3 weeks, when the rats are born it’s only 5-6 weeks before those rats that are born become sexually mature, you know a single female rat if she’s in good condition can have 4 or five litters a year. So I guess my bottom line is I don’t think this lockdown is going to result in any kind of decrease in the rat population for any long period of time."
But it might be a good time to double down on rat control efforts.
“We should capitalize on this time to put out whatever baits and traps and clean up as best as we can,” wondered Corrigan. “And, hopefully the lesson we learned in part from this pandemic is we need to be cleaner.”
No matter how much a municipality spends on rat control, it only takes a few badly managed garbage areas to feed the rats. “When you take your trash out, ask yourself, ‘do I do my trash in a way that a rat can’t get to it?’ said Corrigan. “Period. Yes or no? It’s a simple question.”
“The rats are going to take advantage of sloppiness wherever it occurs,” he pointed out. “Parks, subway, alleys, residents, houses, hotels, hospitals—rats are like ‘show us the slobs and we will show you where we’re gonna set up shop!’”