This week we look at the Rusalka, an elemental spirit from Slavic folklore. She is described either as spirit of forest and field or as a water spirit, though in both roles she is a "fertility wight," a being that brings water to the crops and fields. However, by the 19th century the Rusalka became the spirit of women who died unbaptized or as virgins, a kind of vengeful damned spirit. They also became associated with mermaids at this time, and a Rusalka-type spirit is the inspiration for Hans Christian Andersen's "Little Mermaid", which bears a resemblance in plot to Dvořák's opera entitled "Rusalka". I discuss all these associations, as well as reasons for the shift from benevolent but tricky nature spirit to malevolent spirit leading men to their deaths.