Effra (portrayed by Sherry Jackson) is a character in the episode “The Space Croppers.” She is the daughter of Sybilla and the sister of Keel, over whom she seems to have some control when he is transformed into a werewolf. She practises magic and at one point orders Will to provide her with some of Don’s hair after he rebuffs her advances, obviously with the intention of using it for magical purposes. Her mother tells to Dr. Smith that Effra revels in the carnage the space croppers’ plants will create, and advises him to “just close his eyes” if Effra levitates him above the feeding plants.