"Land snails, which we normally think of as being rather slow moving, can actually disperse enormous distances by hitching rides on birds," said Richard Preece, of the University of Cambridge, in England in an interview on Wednesday.

A genetic analysis of snails from the isolated islands, which were thought to be unique to them, revealed they belong to the genus Balea just like their European cousins.

"We have shown that they are indeed exactly the same genus as Balea," said Preece, who reported the finding in the journal Nature.

The arrival of the snails on the islands predates their discovery by humans. So the scientists believe the European snails which cannot swim or fly travelled the 9,000 km (5,592 miles) to the Tristan da Cunha islands on birds.

"It must have gotten there, we think, on some sort of migrating bird," said Preece, adding it was probably a wader.

The genetic trail suggests the snails dispersed from Europe to the Azores and the Tristan da Cunha islands and then back again.