The Medusae conquered the Moon, set up their bases there, and went on to attempt conquest of the Solar System. The Medusae had for eons used a reddish, artificial greenhouse gas to keep their dying world from freezing. The Medusae learned from the first human expedition to their world that the gas rots human flesh, and the Medusae use it as a potent chemical weapon, attempting ecological destruction by means of projectiles fired from the Moon. Their vast spaceships also have very effective plasma weapons, very similar to those the Romulans had in a Star Trek episode called "Balance of Terror".