New Zealand’s recent announcement of a plan to eradicate all invasive predators, including feral cats, sparked an immediate response—and not in defense of the stoat, up there with cats among the top 100 on the Global Invasive Species list. “Cat murdering New Zealand[ers] are for the birds,” one commenter vented on The Washington Post’s website. “Removing cats from an area is a futile effort—one that cannot succeed,” another warned. When Australia announced a plan in 2015 to cull 2 million feral cats, the singer Morrissey declared them “2 million smaller versions of Cecil the lion.” The actress Brigitte Bardot called the cull “animal genocide.” Needless to say, no celebrity outrage or online indignation has greeted New Zealand’s or Australia’s expensive and long-standing rat-eradication programs.

What makes an animal a pet—a creature to which our emotions attach, sometimes in logic-warping ways—is surprisingly difficult to pin down. Cats are a particularly puzzling case. Domesticated some 9,500 years ago, they still don’t strike humans as completely tame. They live with us, but even indoor cats aren’t entirely dependent on us, certainly not in the emotional way dogs are. They do many things that seem to defy rational explanation, which is no small source of their allure: the blanket-attack ritual, the full-body keyboard plop, the blank-wall stare, and perhaps most dramatic, the post-poop freak-out. One of my cats performs a ninja leap about three feet up one side of the door frame, then slides down, firefighter-style, to the floor.

Even the discoveries, in the past several decades, that cats carry a parasite that could contribute to schizophrenia, and that outdoor cats wreak ecological disaster, haven’t budged a curiously imbalanced relationship with this furry companion—or maybe cohabitant is more accurate. More than a third of all households in the United States now have a pet cat (the total count is estimated to be close to 100 million animals), which marks a 50 percent rise since the 1980s. Their owners feed them, stroke them, shovel their litter, spend ages trying to photograph their yawns from the cutest angle for Instagram. They ignore their owners, mostly sleep, intermittently deign to serve as purring lap warmers, and occasionally drop a half-dead mouse on the rug. Mysterious as cats are, however, the greatest mystery about cats centers on humans. Why do so many of us love them so much when they are so bad for us, and for our planet? And if we could resolve this first mystery, would we be any closer to solving the world’s cat problem?

In Cat Wars: The Devastating Consequences of a Cuddly Killer, Peter P. Marra, the head of the Smithsonian Migratory Bird Center, and Chris Santella, a widely published travel writer, take the easy way out. They’re so clearly not cat lovers that they can’t really begin to comprehend those of us who are. The best they can do in their otherwise informative anti-cat polemic is to tell us that cats have long been “tolerated by their human neighbors because of their supreme pet-like characteristics.”

Merely tolerated? Rat-catchers aboard colonizing ships in the 18th and 19th centuries, cats immediately inspired a craze when they were introduced to islands in the Pacific, the reporter Abigail Tucker writes in The Lion in the Living Room: How House Cats Tamed Us and Took Over the World. “A passion arose for cats,” according to the log of a ship that landed in Samoa, “and they were obtained by all possible means.” Tucker takes an intriguing stab at accounting for that still-thriving passion. “Cats look uncannily like us,” she proposes, and locates their appeal not in their alien aura but in the spell their familiarity exerts and the protective fascination it elicits. “Even better, they look like our infants.” Given their baby-size bodies; large, front-facing eyes; and yet oddly predatory mien, it’s no wonder we find them “mesmerizing.”

Tucker is certainly right to suggest that the current cat predicament is rooted in peculiarly fraught power relations between these cuddly yet opaque creatures and Homo sapiens. History reveals felines as the ultimate opportunists, biologically primed to exploit their human enablers—among many other creatures. As both books reveal, cats travel well, reproduce quickly, and are savage and omnivorous predators. When Mark Twain arrived in Hawaii in 1866, some 90 years after cats had strolled down the gangplanks of Captain Cook’s fleet and conquered the hearts of the natives, he observed “platoons of cats, companies of cats, regiments of cats, armies of cats, multitudes of cats.”

The bloody takeover was well under way, and has continued. Those felines, who have since multiplied in feral-cat colonies throughout the archipelago, prey on endangered birds such as the petrel, the nene, and the Laysan albatross, and have helped decimate the Hawaiian crow. In Australia, with its 3 million pet cats and 20 million feral cats (and about 23 million people), cats have contributed to wiping out several mouse, rat, and bandicoot species. They currently threaten the much-beloved greater bilby. Cats are implicated, according to one study, in 14 percent of all reptile, mammal, and bird extinctions on islands—33 animal species in all.

Princeton University Press

And the feline menace isn’t limited to islands. Cats imperil species around the world, including our own, with which their relations have become—at least on the surface—more symbiotic. A century ago, when they were still viewed as a quasi-domesticated form of vermin control, cats were also regularly deemed vermin themselves—a germ-carrying danger to be treated as such. The New York SPCA, for instance, gassed 300,000 strays during a 1911 polio scare. The invention of kitty litter in 1947 heralded the thoroughly housebound cat, and a new identity, or rather, disguise: The pampered pet had arrived, but the semi-pest still lurked.

Toxoplasma gondii, mostly found in outdoor cats, is one of the most common parasites in humans. It is present in nearly half of the world’s population, according to estimates. Often acquired by eating undercooked meat from animals who ingested tainted cat poop, it can cause a disease called toxoplasmosis, which is especially dangerous for infants and the immunosuppressed, but may pose risks for others as well. Carriers of the parasite seem to suffer at higher rates from Alzheimer’s disease, anxiety, migraines, bipolar disorder, suicidal tendencies, and obsessive-compulsive disorder. There’s evidence for a schizophrenia link, too. And in a twist worthy of a Cheshire Cat smile, Toxoplasma gondii may change our behavior in some bizarre ways, actually encouraging an attraction, in men, to cat pee. (In “How Your Cat Is Making You Crazy,” which appeared in these pages four years ago, Kathleen McAuliffe reported on pioneering research into the parasite’s effects.)

Stop and think about the adaptive brilliance: More humans seduced by house cats means more besotted allies willing to take to the barricades in defense of all cats, ignoring the broader free-ranging-cat menace. And it is broad. Toxoplasmosis also afflicts nonhuman animals, from beluga whales to kangaroos. Because of runoff in the ocean from sewage containing cat feces, the disease has seriously affected marine mammals like seals (including the endangered Hawaiian-monk variety), sea otters, and manatees over the past several decades.

A 2013 study co-authored by Marra estimated that outdoor cats in the U.S. kill—not by disease—somewhere between 1.3 billion and 4 billion birds and between 6.3 billion and 22.3 billion mammals each year. It’s fair to say, as Tucker does, that cats may be considered “nightmarish invaders, capable of ransacking whole ecosystems and annihilating feebler life-forms in their path.”

If that characterization calls to mind another species (our own), perhaps it shouldn’t be a surprise that solutions for the cat problem have proved hard to come by. Both of these books emphasize that altruistic impulses and calmly rational responses have been in notably short supply. As birders have become poignantly aware of cats’ impact on biodiversity, two camps have dug in: cat people and bird people. Extremism reigns in a war of Tom and Jerry–esque brutality over how to handle the free-ranging-cat problem. Bird people want all outdoor cats to go. Some have gone vigilante and poisoned or shot strays. Cat people have fought back, occasionally with death threats of their own—against people.

Simon & Schuster

Even if compromise did seem more feasible, both books suggest that a moderate and affordable solution doesn’t really exist. The primary answer, at least in the United States (host to roughly 100 million outdoor cats), is trap-neuter-return. The approach, popular in many counties, involves just what the name suggests, with cats ideally returned to the cat communities they were part of, now spayed and under the official or semi-official auspices of “managers.” Proponents argue that TNR prevents rampant breeding, and is more humane than euthanasia. But TNR, according to Tucker as well as Marra and Santella, is not especially effective at accomplishing its primary stated goal of keeping cat populations in check. To do that, you’d need to spay or neuter nearly all the animals in a colony, whereas most TNR programs target a small fraction. So the cats continue to breed—and hunt. They routinely get fed, too, by the colony supervisors. As one article in a scientific journal put it, the practice is “cat hoarding without walls.”

Eradication, which has been tried on about 100 islands (from the Galápagos to California’s San Nicolas) over the past 30 years, is usually successful—but can be hard-won and very expensive, even in a self-contained space. To dig out every last kitten from an island’s rocky crevices costs up to $100,000 per square mile. Herding cats isn’t easy. Most programs use traps and toxic bait; some rely on “specialist cat-hunting dogs.” And then there are the daunting public-relations challenges.

With their eye on non-island countries, namely America, the authors of Cat Wars argue for a combination of spay/neuter programs, enclosed sanctuaries, and euthanasia. But they’re well aware of the obstacles. “We would find it preferential—if not quite realistic—to see all free-ranging cats removed from the environment,” Marra and Santella write. The not quite realistic is as much a nod to the power of pro-cat sentiment in the United States as it is to the practical impossibility of somehow stashing all the stray and feral cats in giant, smelly cat houses. They may well be right that the political difficulties are more daunting than the logistical ones. (Good luck even getting cat owners to keep their pets inside; according to studies the authors cite, 40 to 70 percent of house cats are allowed to roam, and the majority of them spend their time doing what outdoor cats do—hunting.) When a Kiwi philanthropist and activist named Gareth Morgan launched a website supporting an outdoor-cat-free New Zealand back in 2013, he said much of his hate mail came from America. “It really feels like I’ve taken on the gun lobby,” he told Tucker.

Guns don’t purr, of course, or lie across your belly at the end of a long day like a small, furry pillow. Then again, cats—however cute—are lethal and heartless. That’s essential to their charm, I would argue: We care about cats so much because (unlike babies) they really don’t care about us. Even their purring seems to be all about them. They are egotistical and self-sufficient, and not really house pets, and we like the sense that we’re more dependent on them than they are on us. Otherwise we would get dogs. To make the rest of nature pay the price for that preference, though, is an act of supreme selfishness. You might think we were spending a little too much time with our cats.