In Patricia Highsmith’s unnerving 1964 short story “The Snail-Watcher,” a broker’s quiet fascination with breeding garden snails curdles into a terrifying biological reckoning that ends with him entombed by his own neglected and ever-multiplying subjects. The tale, a claustrophobic master class in the hubris of human interference, offers a bleak twist on the frailty of humanity’s supposed dominion over nature.
“The Snail-Watcher” finds a startling real-world echo in French Polynesia, where well-meaning ecological interventions have backfired with catastrophic precision. During the 1980s, Partula snails, a genus of aspirin-size tree mollusks with more than 100 species and subspecies across the Society Islands of French Polynesia, nearly vanished after the arrival of a carnivorous foreign snail. (That snail had been introduced a decade earlier in an attempt to control a different invasive snail.)
Partula is re-establishing its place in Pacific ecosystems because of a pioneering rescue initiative that began in 1991 and now includes 15 zoos around the world. Led by the Zoological Society of London, the alliance focuses on captive breeding and reintroduction. Recently, more than 7,000 Partulas of various critically endangered species and subspecies were introduced across four French Polynesian islands — the largest undertaking of its kind.
Snails have been both protagonists and antagonists in the islands’ modern history. “Meddling humans have engineered quick fixes without fully grasping the chaotic, long-term repercussions,” said Paul Pearce-Kelly, the curator of invertebrates and fish at the Zoological Society. And Partulas hold immense research value, despite their small size. “They’re the Darwin’s finches of the snail world,” Dr. Pearce-Kelly said. “They have been under scientific scrutiny for more than a century, offering a unique, real-time look at how isolation drives evolution.”
Thirty-five years ago, a colleague of Dr. Pearce-Kelly rescued the nine last-known members of Partula tohiveana, a species commonly known as the Mo’orean viviparous tree snail, which led to the Zoological Society’s conservation effort. To date, the organization and its partners have returned more than 30,000 snails to Mo’orea, Tahiti and other Pacific islands, including 11 species and subspecies once considered extinct in the wild, into predator-proof reserves. Before release, and to aid monitoring, each snail’s shell is dabbed with fluorescent paint that glows blue under ultraviolet light.
Timothy Pearce, head of the mollusks section at the Carnegie Museum of Natural History in Pittsburgh, described the program as a critical model for mitigating human impact on fragile island biodiversity. Decades of intensive conservation paid off two years ago with the discovery of wild-born Partula tohiveana on Mo’orea; the species was once deemed lost. This success was closely followed by the discovery of a wild-born Partula varia on Huahine, the first time in three decades that the rare snails had naturally repopulated their native habitats.
Shell games
The road to extinction is often paved with good intentions and poor science. Hawaii learned this lesson the hard way after introducing the giant African land snail (Lissachatina fulica) in 1936. The snail, which grows to nearly a foot long, was intended to be a food source, but it multiplied rapidly and became an agricultural nightmare. Within two years, it was ravaging crops and even stripping the stucco from buildings.
“It is a natural dynamic that when a species is placed into a new environment where it has no competition and there are no native predators, it can thrive,” Dr. Pearce-Kelly said.
In 1955, in a misguided attempt at biological control, officials drafted the rosy wolf snail (Euglandina rosea), a three-inch-long snail native to the southeastern United States. Armed with specialized chemical receptors, the rosy wolf snail proved to be a ruthless tracker, following slime trails with astonishing speed.
“It’s about three times faster than typical snails, allowing it to easily overtake prey,” Dr. Pearce-Kelly said. But the wolf snail ignored its intended target, instead using its powerful neck to pin down and devour vulnerable native species.
In 1974, ignoring the cautionary evidence from Hawaii, French Polynesian officials unleashed the “cannibal snail” on their own delicate island ecosystems. The wolf snail, capable of consuming 350 victims in its brief two-year life span, began a relentless march through the smaller Partulas. Dr. Pearce Kelly described a gruesome feast in which the predator consumes its cousins whole, systematically erasing species that had thrived for hundreds of thousands of years.
By 1994, the rosy wolf snail had wiped out 43 of French Polynesia’s 61 native snail species, pushing the survivors to the brink.
“Despite warnings, no one ever listens when there are what sound like easy solutions or opportunities for short-term,” said Justin Gerlach, a plant biologist at the University of Cambridge. “As a result, conservationists spend our time trying to undo the mess, which isn’t as easy as it sounds.”
In French Polynesia, the native Partulas play a crucial ecological role clearing forest fungi; Dr. Gerlach called them “cleaners of the tropical forest.” Their rapid decline has disrupted vital nutrient cycling and weakened forest health; it has also severed a deep, millennium-long link to Polynesian culture and traditional artistry.
Conservationists are reintroducing Partulas into the forest canopy to avoid the latest challenge, the ground-dwelling New Guinea flatworm (Platydemus manokwari). While the flatworm poses a threat to Partulas, it has unexpectedly throttled the spread of the rosy wolf snail — a typical result of the “boom and bust” dynamic between old and new invaders, Dr. Gerlach said.
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