Japan Exterminates Killer Mongooses That Just Had One Job

Mongooses deployed on a small Japanese island to cull a population of venomous snakes have themselves been culled by the state, after the mammals insisted on eating the local endangered rabbits.

Mongooses (yes, that’s the plural) are venom-resistant and prey on venomous snakes like those on Amami Oshima, a subtropical island and UNESCO World Heritage site that is home to species like the Okinawa rail, the Iriomote leopard cat, and the endemic Amami rabbit.

It was that endangered rabbit—often referred to as a “living fossil” for its resemblance to ancient Asian rabbits—that found itself at the mercy of the small Indian mongooses (Urva auropunctata), introduced in 1979 to reduce number of habu, a pit viper, on the island.

But there were issues with the plan. For one, mongooses are diurnal and the habu are nocturnal, meaning the two animals rarely crossed paths. Instead, the mammals turned their gaze—and their appetites—on the Amami rabbits, drastically reducing numbers of the already threatened species. The mongooses also had a significant impact on Ryukyu long-furred rat populations, according to a Japanese environment ministry release.

The impact of the mongoose population became clear by 1993, and the ministry developed a model project to evaluate the extent of the animal’s harm. By 2000, the mongoose population was as high as 10,000 animals, AFP reported, and Japanese officials began a program to cull the predators.

The program was a success, and by 2007 the mongoose population numbered around 1,000 individuals. Yesterday, the government declared that Amami Oshima is officially mongoose-free, closing the loop on a population control plan gone horribly awry. It took nearly 25 years to rid the island of the mongooses and nearly a half-century to bookend the entire endeavor.

“(This) is genuinely good news for our prefecture and for conservation of World Natural Heritage site Amami’s precious ecosystem,” said Koichi Shiota, a local governor, in a statement quoted by AFP. “There are many lessons we should learn from the impact on native ecosystem that mongooses brought, and efforts and costs required for us to eradicate it.”

The poorly thought-out plan is a reminder of the harm invasive and introduced species can cause to populations that have no defenses against those creatures. The species can wipe out native ones, damage human agriculture, and generally wreak havoc on environments.

Stateside, the last few months were declared Joro spider summer by local researchers who said that the Asian arachnid’s spread across the eastern United States was “a matter of when, not if.”

Though those spiders are not as deleterious to their environment as the mongooses were to Amami Oshima, invasive species should generally be kept from getting a foothold in new environs. Once the animals set up shop, they’re not as easy to kick out. It took 50 years to get the mongooses off a small island—imagine the difficulty with getting spotted lanternflies out of the contiguous United States.