Zoo conservationists have bred 300 near-extinct tiny snails and introduced them back into the wild.
Just 21 Madeiran lands snails were found clinging to a rock on Portugal's Bugio Island. They were believed to be the last of their kind.
Experts at Chester Zoo said they had to brave treacherous conditions and climb cliffs to return them to their natural home, which is part of the Madeira archipelago in the Atlantic ocean.
The Madeira government had asked the Chester Zoo experts to help with the snail conservation.
The conservationists had scramble from the water up a cliff face in the dark to find cracks in the rocks where the snails could be safely left.
Tamas Papp, assistant team manager for invertebrates at Chester Zoo, said: "We knew we had one shot to save them.
"If we missed this chance, that was it: they were gone."
