In Tremors II: Aftershocks, the underground creatures were called Graboids. They are the giant subterranean predators that first appeared in Tremors and return as the central threat in the sequel.
The 1996 film follows Earl Bassett and Grady Hoover after they are hired to eliminate a Graboid infestation at an oil field in Chiapas, Mexico. Graboids travel beneath the ground and attack from below, using long, flexible tentacles to seize prey. Their movement makes ordinary defenses difficult, because victims may have little warning before the ground erupts.
Tremors II expands the creatures’ life cycle. After eating enough food, the Graboids develop into smaller, fast-moving creatures called Shriekers. These creatures reproduce rapidly, are deaf, and detect body heat with infrared-sensitive organs. The film’s characters eventually discover this transformation while trying to survive the refinery infestation.
A common mix-up is calling every monster in the sequel a Graboid. Graboids are the original underground form; Shriekers are their later evolutionary stage, and Ass-Blasters appear as another stage in the wider Tremors mythology.