Rotworms

These worms are more of a nuisance than a real threat. Even the greenest warrior can destroy them without much trouble. Rotworms are neither strong in combat, nor poisonous, and thus easily vanquished. They can be found in the swamps and in dungeons.

In both Underworlds, the Avatar also encountered the far more dangerous Bloodworms, a offshoot of Rotworms.

Trivia

 * In Ultima Underworld I the Avatar must use the corpse of a rotworm as an ingredient to 'Wormy Stew' for a troll to progress in the game.