In 1859, Thomas Austin made a very small decorative decision with very large consequences. Austin was a British expat living in Australia, grown newly wealthy through sheep farming, and he had most of the trappings of his new lifestyle in place—the bluestone mansion, the horses, the 29,000-acre estate. All he was missing were some atmospheric reminders of his homeland. So he asked his nephew to bring him some English fauna—a bunch of blackbirds, thrushes, and partridges, and 24 European rabbits. Hunting them would make for a good weekend activity, and besides, he wrote, "the introduction of a few rabbits could do little harm."
His casual proposal had real ramifications. Austin got his two dozen rabbits, but within a decade, there were enough bunnies on the continent that not only did every one of his shooting expeditions net hundreds: two million were being trapped each year without denting the droves. In 1920, at the peak of the population boom, Australia was the reluctant home to an estimated 10 billion European rabbits—an average of 3,000 per square mile. Since then, neighboring species have suffered under their voracious rule. Whether or not the rabbits can be stopped will affect Australia at all levels, from the submicroscopic to the governmental.
The European rabbit may look innocent, but behind that cute twitchy nose is an eating, digging, breeding machine, with efficiency-ensuring adaptations that would make a productivity guru blush. Though they have their favorite foods, if pressed, they'll eat pretty much everything that is, has been, or ever will be a plant (including their own poop–a strategy called "refection" that helps them absorb as many nutrients as possible). Similarly, they can live in otherwise vacant and inhospitable places, because their homes are vast, complex warrens, huge underground worlds in which they play out their strange hierarchical rabbit dramas.
Even their sex lives–a part of existence that in many other animals is rendered inscrutable by evolutionary tricks–are profit-maximized. Female rabbits experience "induced ovulation," in which sexual activity releases eggs, increasing the likelihood of a pregnancy. Between this and her short gestation time, a rabbit might mother 30 offspring per year, every year, throughout her nine-year lifespan. A bit of quick math puts this at over 250 kits per mom. As one account puts it, "few animals are as far from extinction" as the European rabbit.
Still, bunnies can't hop across the ocean or over mountain ranges. Left to their own devices, they couldn't pull off a solo world takeover. But luckily for them, they've got a better-traveled species on their side—humans. At the end of the last Ice Age, all the rabbits in the world lived on the Iberian Peninsula, and in small areas of France and Northern Africa. But, with the help of their human accomplices, the rascally creatures steadily invaded the rest of the world.
During their travels, the ancient Romans developed a taste for rabbit with garlic and olive oil, and imported a herd or two back to Italy. Centuries later, the Normans took them along to conquer Britain. When the British became the conquerers, they brought them wherever they went, shipping them to their expanding array of colonies and dropping them off on remote islands so that the explorers would have food when they came back. Now, there are established wild European rabbit populations on every continent except Antarctica.
Their expansion, like most, isn't innocent. Gardeners know them as vegetable-chomping pests, but all that indiscriminate digging, eating, and displacing takes a real toll on native plants and animals, too. In places like Australia, where there are few natural predators to balance things out, the results have been catastrophic—the rabbits outcompete small native mammals like bilbies and bettongs, nibble down trees, grass and shrubs to the point of no regrowth, and erode vast areas of land with their warrens. They're not any nicer to Australian consumers, who, according to a 2012 study, pay more for rabbit-affected commodities like lettuce, broccoli, and wool.
The problem is bad enough that Australia has implemented a series of "so-crazy-they-just-might-work" fixes. In the late 19th century, the government put a price on their tails and set the continent's infamous population of bounty hunters on them. (The bunnies bounced back.) In the early 20th, they built a million-dollar, 2,000-mile fence across the continent—at the time the longest fence in the world—to keep the rabbits out of cereal farms in the South. (The rabbits dug under it with ease.)
In 1950, the scientists resorted to germ warfare, introducing a deadly virus called Myxoma into the population. Myxomatosis nearly wiped out the entire rabbit population, killing 99% of the population in some areas—but the .2% remaining quickly repopulated the continent with disease-resistant rabbits. Researchers are now experimenting with another disease, calcivirus, but its returns are also diminishing; new, slightly more humane hope lies with a technique that prevents rabbit eggs from being fertilized without disturbing the rabbits themselves or their complex social systems.
Even if these fixes work, complete healing still might not be possible—a recent study of sub-Antarctic archipelagos, similarly plagued by rabbits, found that the animals had altered their habitats' very soil composition, enough that it hadn't recovered even 20 years after the islands were declared rabbit-free.
Even if the foe is vanquished, Australia's strange, protracted rabbit war may have consequences for decades to come. Maybe it's time to pause the War on Cats.