New York City Just Found a Way to Stop Its Rat Epidemic. Here’s How

So here’s an unsettling fact. One pair of rats can birth up to 15,000 offspring a year – and then those offspring have babies, and so on. Needless to say, no city wants a baby boom of rats happening in its sewers and alleys. One answer to this New York City is looking into is rat birth control.

For decades, the city has used lethal rat poison to keep its rodent population in check, but that can only do so much. Starting next month, the Department of Health and Mental Hygiene will launch a new pilot program that uses a non-lethal drug that simply makes the rats infertile, to stop them from reproducing.

“When you are up against one of nature’s most successful breeding machines, you can never get ahead by killing,” said Dr. Loretta Mayer, the CEO of SenesTech, which manufactures the compound.

The compound has been dubbed ContraPest and was developed by retired University of Arizona professor Patricia Hoyer, who began working on the drug back in 1989. The chemical in ContraPest, 4-vinylcyclohexene diepoxide (VCD), was originally viewed as a toxic compound said Hoyer, but when discovered that it damaged the ovaries in female rats, it was developed into a bait. The liquid bait doesn’t harm larger animals, because of the low dose of concentration. It was only recently approved by the Environmental Protection Agency.


The liquid bait works by triggering early menopause in females, rendering their ovaries infertile in a matter of weeks. The drug also impairs the testicles in male rats to produce sperm. “They put sugar in it and oil and fat, things to make it taste good,” said Hoyer. “The rats love it, and they remember it tastes good, so they go back for more.”

The Metropolitan Transit Authority ran a million dollar six-month trial of the “fertility management bait” in parts of the city’s subway system back in 2013. The results proved promising and an MTA spokesperson confirmed they were planning to expand to other parts of the subway system, which any New Yorker knows is rodents’ favorite.

In 2016, the city tried another experimental method that involved dropping dry ice into rat burrows found in the city’s public parks. This was an effort to eliminate the use of toxic poisons that can harm humans and other wildlife. The dry ice would melt into carbon dioxide and suffocate the rats in their own burrows.

“When selecting products, we look at the least toxic methods that will be effective in reducing the rat population,” a Health Department spokeswoman said in a statement.

City mayor Bill de Blasio has been dedicated to wrangling the city’s rat population which has been estimated at 2 million, and earned the big apple a rodent reputation that it would like to shake. In 2015, the mayor dedicated $2.9 million to expanding the city’s anti-rat program, beefing up the nine-person staff to fifty, and cracking down on areas that were known to have an abundant population.

Rats have long been one of the most prominent forms of urban wildlife and are known carriers of pathogens causing diarrhea, vomiting, and fever in humans. Their fleas are known to have been the culprits for spreading such diseases as bubonic plague, typhus, and spotted fever, so the city is looking into any safe measure that can be used to curb their population.

“The potential for worldwide use is tremendous because rats are pests around the world,” added Hoyer. “It will get rid of them in the places where you don’t want them.”

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