Very little is known about the M-113 creature, except that it needed salt to survive. It used mind control to hide it's true appearance and to immobilize it's prey. The M-113 creature was part of a species that slowly went extinct when the salt resources ran out on the planet. It killed Nancy Crater, wife of Robert Crater who was working on a geological dig on M-113. She was also one of Dr. Leonard McCoy's former girlfriends. Robert Crater continue to provde salt for the creature to help it survive. In return the creature gave him companionship... something Crater craved after the creature killed his wife for the salt in her body. The creature could consume salt orally or through suckers on it's fingers. When the U.S.S. Enterprise arrived at M-113 several crew members were killed by this creature when Robert Crater failed to warn them about the creature. Eventually this creature even killed Robert Crater for the salt in his body.