In the fifth episode of the six-part story "The Web Planet," the Doctor (William Hartnell) is unsuccessful in his efforts to immobilize the Animus, the spider-ish parasite that controls the planet Vortis. Meanwhile, the butterfly-like Menoptra invade the planet, hoping to topple the ant-like Zarbi ruling class (who are themselves the slaves of the Vortis). To say that the Menoptra's efforts are doomed to failure would be putting it mildly. Written by Bill Strutton, "Invasion" first aired on March 13, 1965. ~ Hal Erickson, Rovi