"The problem is that these are land snails and they don't like salt, as you well know," said the University of Hawaii's Robert Cowie, a snail researcher who is working on a very similar, but far larger, study on the dispersal history of Pacific land snails.
Salt water pretty much rules out one common way for animals and plants to reach islands: by raft.
In fact, it was Charles Darwin who tested whether self-sealed land snails could survive on logs or other floating debris. In the end, he preferred the idea that birds brought them.
But there is a third possibility, says Cowie. The snails might have flown without birds.
There have been wind tunnel studies of how far juvenile snails from Greek Islands can blow in the wind. It has been calculated that small snails can be blown more than 10 miles.
"In the Pacific we have even tinier snails," said Cowie. What's more, most of them live in trees, where they could conceivably be caught on a freed leaf during a hurricane and carried for thousands of miles.
"So there's that scenario, which makes it even more possible to imagine flying snails."
To get the present numbers and diversity of snails on the Hawaiian Islands, for instance, Cowie and his colleagues figure that they'd only need one snail-carrying, hurricane-driven leaf to reach the islands every 10,000 years.
As for the Tristan da Cunha Island snails, it could be birds or storms that brought them there, said Cowie. At present, there is no easy way to find out.
