This clearly has nothing to do with human agency. These dispersal events happened long before humans were around.

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One of the species on the Azores returned to Europe. It seems that having got there in the first instance a very long time ago, it relatively recently migrated back to Europe.

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It must have gotten there, we think, on some sort of migrating bird.

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Darwin stuck snails on ducks' feet and submerged them in seawater and found them to die quickly on exposure.

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Land snails, which we normally think of as being rather slow moving, can actually disperse enormous distances by hitching rides on birds.

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I think because they live in trees and are particularly sticky, they're prone to being carried by birds.

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Trying to get one of those birds and the snails together is problematic. So I suspect that some type of wading bird, with a cargo of stowaway snails tucked into its feathers, was blown off course by a storm and deposited the snails on these islands.

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