(Michael S. Williamson/The Washington Post)

Rats. In New York, they can outnumber humans four to one, and at any given time, anywhere between 2 million and 32 million wild rats roam the five boroughs. Given their sheer numbers, you’d think scientists all over the city would be clamoring to get a piece of the rat action. You’d be wrong — and one group of rodent researchers want to change that. Medical entomologists and biologists are working together to change the way the city sees rat, one squeaking rodent at a time.

At times, Michael Parsons sounds more like an urban poet than a rodentologist who spends his winters stalking and trapping the rats of New York.  He calls the rodents "our shadows, our ghosts." The behavioral ecologist, who is a scholar-in-residence at Hofstra University, recently published a protocol for recruiting and tracking urban rats — mammals with serious health ramifications for human beings — in the journal Frontiers in Ecology and Evolution.

The creatures eat at the same “table” as humans, he explains, adapting their diet to the one we prefer. “They tend to share our dietary interests,” Parsons said. “If we eat caviar and hot dogs, rats are going to favor caviar and hot dogs as well.” In part due to that adaptability, rats and humans tend to go together. (Remember Pizza Rat? It’s a perfect example of this sometimes hilarious connection.)

A video of a New York City subway rat grappling with a slice of pizza has become an Internet hit. (YouTube/Matt Little)

They may coexist, but rats tend to cost humans a lot. By some estimates, humans in the United States spend some $19 billion on the losses and damages — including the costs of stolen food and fires resulting from gnawed electrical wires — caused by rats each year. And then there’s disease. Rats feed on the waste generated by city life, but they also have a unique ability to harbor microorganisms, taking diseases with them as they scurry to and fro. That’s gross, but it wouldn’t be a problem if scientists knew a lot about how wild urban rats behave and which diseases they carry. Spoiler alert: They don’t.


A rat being sedated for the new study. (Parsons)

“More than 43 percent of all mammals are rodents, but less than 1 percent of all mammalogists would refer to themselves as rodentologists,” Parsons said. That means that relatively few scientists even bother to study rats — and that when they do, big breakthroughs sometimes follow. In 2015, for example, a group of biologists collected 133 Norway rats (Rattus norvegicus, the most common form of urban rat) from all over New York, then tested them for viruses. Not only did the rats carry pathogens associated with gastrointestinal distress in humans, but they also carried a whopping 18 pathogens that had previously been completely unknown to science.

With that potential in mind, Parsons and his colleagues decided to try not just to collect city rats, but to track their movements throughout New York. Rats’ love of sewers, subways and other subterranean locales presented a particular challenge, so the team decided to lure the animals rather than chase them to their lairs. They used peanuts to tempt rats to humane traps in different locations around a RFID antenna. Using a mobile lab, they anesthetized, microchipped and measured the rats. Then they released them where they were picked up, placing soiled rat bedding around the antennae to be sure they'd return.


A microchipped rat ready to return to the sewers. (Parsons)

This system, which took advantage of rats’ love of rat pheromones to make sure they came back to the antenna again and again, allowed the team to study the rats over time instead of relying on extermination or random chance.

Trapping and tracking rats may sound simple enough, but it’s unique enough that Parsons and his team knew they had to document their methods for others to use. Their recently published protocol is like an instruction manual for rodentologists — but for Parsons, it’s just the beginning. Next, he wants to figure out how to broaden the pilot to all five boroughs and start to understand just how rats carry and introduce diseases into the humans they live with.

He’s up against a big barrier, though: the gross-out factor. “I’m sure I have shed tears over the social taboo issue,” Parsons says with a sigh. “This is like the best example of cognitive dissonance ever.” Not only is it difficult to get businesses and residents to allow research on their property due to fears over privacy and exposure to public health officials, but it’s also hard to find funding for what are widely considered to be annoying vermin. Parsons hopes that he can eventually get enough public interest to fund rat research in conjunction with health officials or public works projects.

Until then, though, he’ll continue to study rats with or without the help of others. “Every day I go out there I feel like I’m learning something entirely novel, or at least something that has not been reported in the scientific literature,” Parsons said. Perhaps humans have even more to learn from Pizza Rat after all.

Erin Blakemore (@heroinebook) is a freelance journalist from Boulder, Colo. She is the author of "The Heroine’s Bookshelf" (Harper). 

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