The Graboid is the main creature of the creature film series Tremors. First spotted in the small town of Perfection, Nevada, they have since also appeared in Mexico and Argentinia. They live and move underground, only coming to the surface to grab their prey, hence their name.
The two graboid hunters hear a Coyote howling:
Grady: Is that a Coyote?
Earl Bassett: Yup.
(The Coyote howls again)
Grady: Man he better keep quiet.
(another howl only cut short by the sound of it being eaten)
Earl Bassett: Yup.
They hatch from eggs which apparently can lay dormant for more than 300 years. They then grow rapidly to a size of about 10 foot, hunting surface dwellers with their sensitive hearing. They have no sense of sight or smell, so they react to the sound of movement and vibration of the ground. When trying to escape a graboid, it is best to either climb rocks (which they can't dig through) or remain absolutely motionless and silent (so they can't hear you).
Burt Gummer: I am COMPLETELY out of ammo. That's never happened to me before.
Graboids are extremely fast, and can grab their prey wholesale by breaking through the upper earth itself, or just by grabbing them with their tentacles.
Their bodies are heavily armored and almost impervious to regular firearms (As seen in Burt Gummers cellar in Tremors).
Recently discovered evidence seems to point at the fact that they are indeed native to earth as precambian fossils have been found, so theories of mutations and extra-terrestrial origins have been discounted. After growing to full size (the duration of which depends solely on the food supply), graboids metamorphose into the surface dwelling Shriekers (Tremors II), the next step in the reproductive cycle of the Graboid. The third stage is the Ass-Blaster, capable of rocket propelled flight (Tremors III).
Watching the movies
IMDB for the Quotes