Thousands of snails traveled more than 9,300 miles in an airplane to reach the islands of Moorea and Tahiti last month. But the gastropods weren’t visiting for a tropical vacation in French Polynesia. Instead, they had an important job to do: restoring balance to the islands’ delicate ecosystems.
The jet-setting creatures are species of Partula snails, also known as Polynesian tree snails, that are extinct in the wild and critically endangered. For the last three decades, scientists and conservationists at zoos in the United Kingdom and the United States have been working tirelessly to bring them back from the brink of disappearance. And their efforts have been paying off: Nine years ago, teams began slowly reintroducing Partula snails into the wild.
The most recent reintroduction, which took place in April, is believed to be the largest wild release of any extinct-in-the-wild species ever, as it involved more than 5,000 snails, according to a statement from the nonprofit Zoological Society of London, which helps coordinate the conservation efforts. Zookeepers and veterinarians at the London Zoo, the Whipsnade Zoo, the Royal Zoological Society of Scotland and the Saint Louis Zoo raised the snails in captivity ahead of their release.
“This was a win for the ongoing conservation efforts of these highly endangered snails,” says Kayla Garcia, zoological manager of invertebrates at the Saint Louis Zoo, in the statement.
To ease monitoring efforts, scientists painted a dot of red UV-reflective paint on each snail’s tiny shell to make them more visible at night, which is when they are the most active. The Partula species are small—measuring less than an inch in size—but they have a big ecological impact by eating fungi and decaying plant matter to keep the forest healthy.
The saga of the traveling mollusks is a long and winding one that dates back to the late 1960s. At that time, French authorities had brought captive African giant land snails to French-controlled islands in the South Pacific Ocean as a source of food for the people living there. But the non-native snails escaped, multiplied and became invasive, wreaking havoc on the islands’ ecosystems.
To help combat the hungry pests—which can eat more than 500 different species of plants—authorities introduced yet another snail, the predatory rosy wolf snail. But instead of going after the African giant snails as planned, the rosy wolf snails began feasting on smaller, easier-to-catch endemic snails, including Partulas. As a result, they quickly drove many species nearly to extinction.
So, in an effort to undo this tangled, human-caused mess, biologists at zoos in London and Edinburgh in the early 1990s rescued the few remaining snails from several decimated Partula species. Together with a dozen other zoos, they launched an ambitious international plan to keep the species going.
Some didn’t make it, though. Only nine individual snails remained from the Partula faba species when they were removed from the wild. But they just couldn’t breed in captivity, and in 2016, the last remaining individual died at the Edinburgh Zoo, rendering the species extinct.
Others, however, have made a miraculous recovery. Since a lone Partula taeniata simulans snail arrived at the Edinburgh Zoo in 2010, conservationists have carefully boosted the subspecies’ numbers back up to several hundred individuals. In total, the partnering zoos have saved 11 snail species and reintroduced 21,000 individuals to the French Polynesian islands.
The invasive rosy wolf snails still live on the islands, but are now extremely rare, as Justin Gerlach, a biologist at the University of Cambridge who is involved with the snail reintroduction efforts, tells Mongabay’s Elizabeth Claire Alberts. That’s because another predator has moved in: New Guinea flatworms. Still, scientists aren’t too worried. They believe that the invasive flatworms will continue to hunt mostly on the ground, while the newly reintroduced Partula snails should take to the trees.
“With nature across the world increasingly under threat, these little snails represent hope for the world’s wildlife,” says Paul Pearce-Kelly, curator of invertebrates for the Zoological Society of London, in the statement.