A button-sized snail once feared extinct in its Bermudian home is thriving again after conservationists bred and released more than 100,000 of the molluscs.

The greater Bermuda snail (Poecilozonites bermudensis) was found in the fossil record but believed to have vanished from the North Atlantic archipelago, until a remnant population was discovered in a damp and overgrown alleyway in Hamilton, the island capital, in 2014.

After a decade-long international effort by conservation scientists, the government of Bermuda and Chester zoo, where thousands of the snails were bred before being transported back to the islands, the species has been confirmed as safe from extinction.

“It’s every conservationist’s dream to help save a whole species – and that’s exactly what we’ve done,” said Tamás Papp, the invertebrates assistant team manager at Chester zoo. “This scientific confirmation that we’ve saved them is testament to the role zoos can play in preventing extinction, and in the power of collaboration, and is something everyone involved will carry in their heart.”

The snails, which are only found in Bermuda, had been hit by global heating and habitat loss, but their decline was accelerated by the introduction of predatory “wolf snails” and carnivorous flatworms, which ate the smaller native species.

At Chester zoo, keepers adapted existing snail husbandry methods to create the best conditions for P bermudensis to multiply, keeping them in specially designed pods.

Since 2019, generations of the captive-bred snails have been returned to islands where they have been placed in protected wooded habitats, with biosecurity measures shielding the species from invasive predators.

The snails have now been found to be well established in six areas, according to a population assessment to be published in Oryx, the International Journal of Conservation, with the species’ recovery hailed on IUCN’s “reverse the red day”, which marks the global effort to repair biodiversity loss.

Dr Mark Outerbridge, an ecologist for the government of Bermuda, said: “It has been extremely gratifying to be involved with this reintroduction programme and to see these snails back in Bermuda’s ecosystem again. It is remarkable to think we only began with less than 200 snails and have now released over 100,000.”

Dr Kristiina Ovaska of the Canada-based partners Biolinx Environmental Research said the restoration of the snails was an important part of restoring degraded ecosystems. “The snails function both as prey for larger animals and as consumers of live and decaying vegetation, so they are vital for turning over nutrients within their habitat,” she said.

The Chester zoo team is now focusing its efforts on breeding a second rare species of snail, the lesser Bermuda land snail (Poecilozonites circumfirmatus).