Giant bloodworms had spotted dark green, slimy skin and a dark brown underbelly. They typically measured 20 feet (6.1 meters) in length. In the dimlight of their underground habitats, they could often be mistaken by other creatures for a moss-covered boulder.
If hungry or provoked, a giant bloodworm attacked by attempting to affix its mouth to a target. Once attached the worm would continue to suck blood from its victim until it was satiated, the victim died, or it was dislodged.
Giant bloodworms were typically known to inhabit shallow pools of water within underground or caverns.