The greater Bermuda land snail was thought to have disappeared for many years until an empty shell turned up in the territory’s capital city, Hamilton.
Live snails was then found among litter in a nearby alleyway.
Some were flown to Chester Zoo for a unique breeding programme.
More than 4,000 snails raised at the zoo have now been taken back to the island and released.
Many more captive snails will soon be returned to their homeland to help give the species a new lease of life.
Mark Outerbridge, a wildlife ecologist for the Bermuda government, said the snail was a “Lazarus species”, which was considered extinct not so long ago.