Goma worms are the actual cause of the "zombie" plague that desecrated the "Forgotten City," or Ebera. Not to be confused with the "Drowned City." After the plague had spread, a number of people with the ability to control themselves from the Goma's infectious blood lust tasked themselves with guarding their fallen city. In the time the group that had come together to save Lyrian had passed through Ebera, Nedwin had collected a sample of Goma worms secretly, because he knew that none of the crew would have agreed with him. When he was nearly slain by Copernum, he had swallowed this sample. When he had died, the Goma worms had enabled him a temporary amount of time to finish what had started with Copernum, and throw himself into a fire to prevent the plague from spreading.
When a group of Ebera Guardians had threatened to keep the Crew stuck in Ebera, they had threatened with tiny sacks of Goma Worms, which would've been used to infect the group. If it had not been for Rachel's quick thinking with Edomic, they might have ended up infected.