Earthworms as a prey source for the insular snake Thamnophis sirtalis (Linnaeus, 1758)

Insular organisms typically evolve in closed, isolated systems; thus, changes caused by introduced species can drastically affect their ecology. Isle Royale National Park (Michigan, USA) is a remote island in Lake Superior that, until relatively recently, was void of earthworms. Its two native natricine snakes are known to feed on earthworms on the mainland; here, we confirm that eastern gartersnakes (Thamnophis sirtalis) are also feeding on earthworms on Isle Royale. It is unknown how this new important dietary source will impact the snake ecology on Isle Royale.