An endangered species of snail unique to Bermuda has been returned to the island after a breeding programme in Britain.

Four thousand of the Poecilozonites bermudensis snails, bred in a joint effort between the Zoological Society of London and Chester Zoo, are being tagged and released by the Department of Environment and Natural Resources.

The snails, thought to be extinct, were sent to London in 2014 after specimens were found living in an alley in the City of Hamilton.

Mark Outerbridge, the department’s wildlife ecologist, said that the return of the snails to their natural habitat was part of a programme to restore the species.

The snails, which date back more than one million years, had last been seen in the 1970s, according to recordings made by Stephen Jay Gould, a paleontologist and Harvard University professor. The snails were common before the 20th century, but numbers declined as a result of carnivorous snails and terrestrial flatworms.

Dr Outerbridge said only a “handful” of residents had actually seen a living endemic land snail.

He added: “However, their fossilised shells are commonly found embedded in the rocks along South Shore.

“I don’t expect they will ever be as numerous as they once were, but hopefully this species will get a new lease of life once it becomes established on the island nature reserves.”

The snails are being released on Nonsuch Island and another privately owned island.

Surveys by the department and a team of volunteers found that both islands have snail-friendly habitats, with no evidence of the predators that almost drove them to extinction.

Breeding and range expansion were observed in a limited number of endemic land snails which were released and monitored on Nonsuch Island in 2016.

That influenced the decision to release a larger number of captive-bred snails.

The department said it would continue to monitor the snails at both reintroduction locations and that additional islands would be selected for future releases.