The Melmacian Cockroach is a blue-eyed insect commonly found on planet Melmac. Although naturally tiny, they can grow to the size of a Human, or even bigger, when exposed to certain earthly chemicals, including boric acid. After Melmac was destroyed, a Melmacian Roach, named Rodney by ALF and Brian, escaped to Earth in ALF's spaceship (in a bag containing a slimeball) and became huge and aggressive after the Tanners' attempts to kill it. Eventually, ALF discovers a substance that is lethal to the Cockroach: perfume.