If internet memes and YouTube videos are any indication, people sure love cats. But some kitties aren’t so cuddly. As many as 6 million feral cats in Australia are gobbling up more than a million lizards a day, according to researchers at Charles Darwin University (C.D.U.), and scientists are worried the felines could push some reptile species to extinction. Feral cats—the untamed descendants of abandoned domestic cats that live in the wild—aren’t a problem just in Australia. An estimated 30 to 40 million of them are roaming around the U.S., according to the Humane Society, and they’re harming native wildlife populations. Recent studies show that feral and outdoor cats kill an estimated 2.4 billion birds and 12.3 billion small mammals a year in the U.S. But just what to do about this “cat-astrophe” is a source of much debate. The Australian government aims to trap and euthanize 2 million feral cats by 2020. Several U.S. cities are using the nonlethal tactic of capturing, neutering, and releasing them so they can’t reproduce. “Because these are animals that a lot of people have as pets, it hits a nerve,” says Brett Murphy, senior research fellow at C.D.U. “But they’re having a huge impact that people wouldn’t normally think about.”