Critically endangered snails bred in a zoo have been set free to wander (very slowly) on a remote Atlantic island

The release brings two species of Desertas Island land snails back to the wild. Prior to this they were believed to be extinct

More than 1,300 critically endangered snails, bred in a zoo, have been released into the wild on a remote Atlantic island.

The release marks the return of two species of Desertas Island land snails to their natural habitat, after they were feared to be extinct for a century.

A small population of the snails was discovered surviving on rocky cliffs on Deserta Grande island, near Madeira, prompting a rescue effort by conservationists.

The snails were taken to zoos in the UK and France, including Chester Zoo, where they were housed in a converted shipping container.

The tiny molluscs are native to the windswept, mountainous island of Deserta Grande, south-east of Madeira, where habitat destruction by rats, mice and goats, introduced by humans, had led to the snails being feared extinct.

But conservation expeditions between 2012 and 2017 found otherwise, discovering just 200 surviving snails on the island.

Believed to be the last of their kind, the snails were collected and brought into captivity.

At Chester Zoo, 60 of the precious snails were cared for by the conservation science team, who recreated the right food, vegetation and conditions for them in miniature habitat tanks.

Now, 1,329 snail offspring, bred at the zoo, have been marked with identification dots - using non-toxic pens and nail varnish - and transported back to the wild for release.

"This is a colour code," said Dinarte Teixeira, a conservation biologist at Madeira's Institute for Nature Conservation and Forests.

"It will allow us to spot them and track where they disperse to, how much they grow, how many survive and how well they adapt to their new environment."

A wild refuge has been restored for the snails on Bugio, a smaller neighbouring island in the Ilhas Desertas (Desert Islands) archipelago.

Bugio is a nature reserve and invasive species have been eradicated there.

Gerardo Garcia from Chester Zoo said the reintroduction was "a major step in a species recovery plan".

"If it goes as well as we hope, more snails will follow them next spring. It's a huge team effort which shows that it is possible to turn things around for highly threatened species.

"These snails are such an important part of the natural habitat [on the islands they come from]," explained Heather Prince from Chester Zoo.

As well as being food for other native species, she explained, snails break down organic matter and bring nutrients to the soil.

"They help plants grow. All of that is dependent on the little guys - the insects and the snails that so often get overlooked."