And that’s just why we’d miss them. By killing mice and rats in barns and grain storage areas, cats are vital for keeping those pests in check. In India, Beck said, cats are believed to play a significant role in lessening the amount of grain loss caused by consumption or contamination by rodents. In other words, it may be true that humans feed cats, but without cats, humans would have less food in the first place.
So, how dramatically would the rodent population increase if cats suddenly vanished? It just so happens that several scientific studies have been conducted that paint a vivid picture. A 1997 study in Great Britain found that the average house cat brought home more than 11 dead animals (including mice, birds, frogs and more) in the course of six months. That meant the 9 million cats of Britain were collectively killing close to 200 million wild specimens per year — not including all those they did not offer up to their owners. A study in New Zealand in 1979 found that, when cats were nearly eradicated from a small island, the local rat population quickly quadrupled.
And if the rodent population shot up, this would of course trigger a cascade of other ecological effects.