This tiny snail is about the size of a grain of rice (5mm long). Chris Waldrup brought it to me after finding it under a log. The snail belongs to the genus Cionella, probably Cionella morseana (the genus also goes by the name Cochlicopa). Reproduction in this genus of snails is mostly through self-fertilization, confusing the taxonomy of the group by creating a star-burst of mini-groups. Studies of European members of the genus have found that some named “species” are collections of multiple lineages.
This snail is the intermediate host of Dicrocoelium dendriticum, a parasitic liver fluke that infects sheep, goats, and cattle. After infecting a snail, the fluke moves on to ants, then finally infects mammals. The following diagram from the CDC summarizes this complex life cycle, although they have drawn the wrong species of snail. Humans can get infected, but only when we eat infested ants, an event that is apparently rather rare.