The fin worm split off from its ancestor in search of a new home that would protect them from the destructive insaneshroom and the notorious wingworm catcher. When they evolved they became slightly bigger than their ancestor. Their wings have become stiffer and are no longer used for flying, but instead for swimming in the water. They also have developed a fish-like caudal fin on their tail, which helps them swim even faster since they are hunted by many predators.
Their diet mainly consists of freshwater raftballs and the seeds of river bubbleweed, though they will occasionally leap out of the water to take small bites out of the leaves of bubble herus. During their mating season, the fin worms migrate to Bone River to gather in huge swarms to mate. Next they lay their eggs under the leaves of river bubbleweed and die. Finally the eggs hatch and swim back to the Bone Swamp from where they came from.