Halfway between Sweden and Finland, and separating the Baltic Sea from the Gulf of Bothnia, lies a vast group of islands known as the Åland archipelago. Consisting of more than 6,500 islands, Åland is home to a species of butterfly known as Granville Fritillary (Melitaea cinxia), which inhabits the small patches of dry meadows that are found on many of the islands1. For the most part, the butterflies on each island form a distinct population. About 60-80% of the butterflies spend their entire lives on the island where they are born. So the butterflies living on each island are almost isolated from the rest of the species.