Rock Worms


 * You feel the ground tremble as suddenly, beneath you, you see a fissure in the earth where none was a second before. You frantically try to move out of the way as a large rocky protrusion lunges straight up out of the ground under you. With cobblestones, rocks, clots of dirt, and shrubs flying in all directions, it flings you into the air. For what seems like a minute to you everything stops. Then, only a matter of seconds later, it stretches upward, suspended in the air by its submerged body, and catches you in its mouth, grinding its jaws over your armor. Your companion, a matter of feet behind you, puts his shield in front of his face, shielding himself from the flying cobblestones and debris and squares his stance. After the barrage he charges forward.
 * -Description of a Rock Worm encounter

History
Natives of the Elemental Plane of Earth, Rock Worms didn't exist on the Material Planes until Sorcerers decided to summon them or they wandered through a stray portal. Since being on the Material Planes, they have reproduced and began to populate the realms that they are on, though their numbers are not nearly as plentiful as on the Earth Elemental Plane.

Biology
They look like regular earthworms although they are exorbitantly larger and have an extremely tough hide composed from rock and calloused flesh, which covers them entirely. Rock Worms are blind, though they are able to "see" by use of an ability known as Tremorsense

Behavior and Ecology
While not necessarily carnivorous predators, rock worms will hunt and consume other living beings on occasion. This is because rock worms need to sustain their bodies by eating carbon-based organisms as a supplement to what they ingest from burrowing. They can cause many problems when near civilization due to their tendency to burrow, which can destroy foundations, supports, mines, and even pipe-systems. When encountered (and subsequently eradicated), they tend to cause a great deal of damage to the natural and built environments. Sinkholes are highly characteristic of a rock worm infestation.

Habitat
Rock worms can burrow through stone (stone is considered difficult terrain), but they are normally found in areas consisting of softer soils such as desert, beach sands, or grassland dirt. When moving through such hard materials it leaves behind a usable tunnel about 5 feet in diameter.

Magical Abilities and Combat
Rock worms normally stay underground. When they feel creatures on the ground above them or when they feel creatures using the tunnels they have left behind, the creature's fight-or-flight mechanism takes over. Rock worms start combat by creating an earthquake, making an intense but highly localized tremor rip the ground. This ability is natural for them, and functions the same way as an Earthquake Spell.

A rock worm will then typically make a charging attack. If overwhelmed it might perform an awesome blow in order to distance itself from enemies or it may writhe around, shifting the earth under aggressors' feet with a tremor. It it feels outnumbered it may burrow underground in order to fight on its own terms. Once there, if the worm's prey drive overrides its fear of death, it will repeat the tactics detailed above.