An Earth-like planet was home to many species of butterflies, a species of flying spider and a species of flower which was deadly to Cybermen and Cybermats.
The Second Doctor, John and Gillian visited the planet, where they met Professor Gnat, who was there to collect butterflies for study, and freed him when he was captured by Cybermen. (COMIC: Flower Power [+]Loading...["Flower Power (comic story)"])