Some of New York’s free-roaming feral cats are being given a chance to make a contribution to their city—as rat exterminators.

Volunteers trained by the city’s Feral Cat Initiative trap feral cats. The felines are then spayed or neutered and vaccinated. The volunteers then return them to their home territory, but some wind up in places with large rat populations.

Four feral cats patrol the loading dock at the Jacob K. Javits Convention Center, where food is delivered and garbage removed, the center’s Sustainability Manager Rebecca Marshall told the Daily News.

“We used to hire exterminators, but nature has a better solution,” she told the paper. “And cats don't cost anything.”

The Javits Center employees lured the four cats to the loading docks about two years ago.

Cats are predatory, but won’t necessarily attack rats. However, the feline scent and droppings will ward off rates.

“A mother rat will never give birth near a predator because the cats would eat the babies,” Jane Hoffman, president of the mayor's alliance, told the Daily News.