New York Is Sterilizing Its Rats. Here's How

A company aims to sterilize some—not all—of NYC’s subway rodents
Photo illustration by 731; Photographs by Don Farrall/Photodisc/Getty Images (birth control); Davies and Starr/Digital Vision/Getty Images (cheese)

No one knows exactly how many rodents reside in New York, but there may be as many rats as humans by some estimates. That’d be 32 million scurrying legs. Rats are remarkably fertile, sometimes birthing 12 pups per litter and as many as seven litters a year. That’s why the Metropolitan Transportation Authority has started a pilot program to sterilize females. It’s teaming with Flagstaff (Ariz.)-based SenesTech, a company that invented ContraPest, a product that, when consumed orally by rats, accelerates egg loss and can cause infertility in days.

New York’s rat extermination proposals in the past have included everything from the deployment of World War I-era poison gas to a hunting spree led by rifle-bearing citizens. (The gas was used with some success on Rikers Island, now home to one of the city’s jails; the hunting party apparently was called off at the last minute.) This is the MTA’s first effort to target the rodents’ reproductive organs.

For the next two months, SenesTech will study rat behavior in New York subways. One goal is to pinpoint preferred foods in hopes of making the ContraPest bait more desirable than discarded pizza and candy. “In New York, rats have such a buffet available to them,” says SenesTech co-founder Loretta Mayer, “but they don’t necessarily get a lot of liquid, which is why we’ll be offering them … a semi-solid covered in kind of a cheese wax and also liquid from a bottle feeder.”

Mayer says ContraPest is made up of mostly salt, sugar, fat, an herb—and an industrial chemical called 4-vinylcyclohexene diepoxide (VCD). The product will be placed inside bait boxes outfitted to monitor rat traffic. The boxes will be placed in subway trash rooms, where garbage is kept until trash trains take it away.

The goal is to diminish rat populations—but not wipe them out entirely, as that would simply cause an influx of new rats. “Rats are territorial, so you want to maintain a very low population that keeps other rats from migrating in,” says Mayer. “That way you won’t have an infestation, you’ll manage them so low that folks won’t see them on the subway tracks anymore.” Mayer, who estimates only two or three rats are needed in each 200-square-foot trash room to keep out new rats, says the goal is to reduce the population by up to 75 percent. Once that target is achieved, bait will be removed from the boxes.

SenesTech has raised $30 million in research funding from the likes of the National Institutes of Health since being founded in 2002. The private company has 20 employees and expects to become profitable in 2014 by licensing its technology to pest management and agriculture products companies. “We feel quite small in the scope of what we’re trying to do,” says Mayer. SenesTech already is running tests in Indonesia, Laos, the Philippines, Australia, and New Zealand, mostly to keep rodents from ruining crops such as wheat and rice. It’s also developing a product to sterilize dogs.

Mayer says ContraPest does not work on people, nor does it pose them any danger. Rats metabolize the compound into inactive ingredients within 15 minutes of consumption, rendering rat excretion innocuous. “And should the compounds spill and be exposed in the environment … it also breaks down into inactive ingredients,” she says. Contra-Pest also doesn’t appear to cause rat mood swings, says Mayer. “As one person said to me, ‘Wow, don’t you worry? I mean, a whole bunch of large menopausal rats—aren’t they angry?’ Well, we’ve not seen that behavior change.”

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