Graboid

Graboids are a species of reptilian creatures from the Tremors series.

One of the characters says of them that "graboids are to the desert what sharks are to the ocean."

Physiology
Graboids are depicted as subterranean, reptilian animals, superficially resembling gigantic worms or grubs, with long, serpentine bodies. When fully grown, a mature graboid will measure up to 30 feet long, and 6 feet across at their widest point, and weigh 10-20 tons. Graboids completely lack eyes; they don't need them, due to living underground. Instead, they sense vibrations. Their heads consist of a massive, black, armored beak, which is used to push aside the dirt whilst digging- there is a wide upper jaw, a thinner lower jaw, and a pair of hooked mandibles on either side.

Graboids have a trio of long, powerful, serpent-like tentacles, which are prehensile and have a reach of at least ten feet. Normally kept retracted in the graboid's throat, these tentacles were initially mistaken for the actual creatures, causing the characters in the first Tremors film to underestimate their underground opponents. The graboid's common name is derived from these prehensile tentacles, which "grab" prey and pull it back down the graboid's hungry gullet.

Presumably, it must also possess a semi-rigid internal structure (though not a true endoskeleton) since it can burst through concrete (though such an impact kills it). Less dramatically, the Graboid's ability to lift its upper body into the air, as well as bear the weight of the soil through which it moves, also suggests a semi-rigid internal structure. The internal cuttle-bone structure is probably coupled with a strong musculature.

They are very hard to kill with anything short of saturation bombing or large-bore rounds, due to their thick, pebbly hide. Graboids possess immense physical strength, able to topple over mobile homes, tow along an object heavy as a pickup truck without slowing down, smash through brick walls and pull an entire station wagon underground. All around their bodies are short spikes, which all move in unison to push the graboid through the dirt, similar to the 'setae' on an earthworm. They are able to burrow faster than a human can run, as they have an armored head and mobile spikes working together in unison. These allow a graboid to "swim" through the loose soil at high speed like a shark in the water, though they are incapable of tunneling through solid rock. Their top speed seems to be around 15-20 mph in good loose soil. Therefore they are able to burrow faster than a human can run; a Graboid cannot not catch motorized vehicles like cars or dirt bikes.

Graboids (and their later forms, the shrieker and ass-blaster) have distinctive orange blood. Graboids also have a powerful stench, which is made evident on several occasions throughout the first film. The Graboid appears to respirate the same nitrogen-oxygen atmosphere as other terrestrial animals. Witnesses have heard Graboids sometimes expel blasts of air. This implies that Graboid's possess lungs. Whether these lungs resemble vertebrate lungs is unknown. The Graboid, Shrieker and AssBlaster all have closed circulatory systems; their reddish-orange blood has been well-documented. This suggests that they possess a cardiopulmonary system, a heart pump and an oxygen-based blood-transport system.

Hunting and intelligence
Graboids are shown to be ravenous carnivores, always on the hunt for food. Indiscriminate eaters, their diet includes sheep, cattle, horses, donkeys, coyotes, and humans. Lacking eyes or a nose, they're shown to hunt by sensing seismic vibrations which are produced by sounds and movements (such as walking). Because they are unable to tell the difference between edible and inedible vibration sources they adopt a policy of "eat first, ask questions later," swallowing whatever sets off their vibration sensors and regurgitating anything that does not taste good. Inedible objects can be spat out with considerable force, being propelled high into the air. Due to the sensitive hearing they use for underground navigation, graboids are so sensitive to sound they must retreat from loud explosions, which cause them great pain.

Graboids are ambush predators, preferring to sneak up on their quarry, though they are shown to chase it down with great determination. They erupt from the ground and use their tentacles to ensnare prey, pulling them into their mouth (sometimes only the tentacles break the surface). The tentacles wrap around the prey, biting into its flesh or hooking the prey with their horn-like spikes. When prey attempts to flee by climbing (for instance onto the roof of a house or car), graboids will dig away the earth under the hiding place, undermining it until it collapses or sinks low enough to allow the graboid to pluck off the prey. When they are unable to break down the prey's hiding spot, the undaunted graboids will continue circling it, like sharks at sea, until it ceases making vibrations. Usually they wait so long the prey dies of dehydration or starvation, i.e. several days.

Graboids are depicted as highly intelligent, possessing memory and the ability to learn. For instance, in the first Tremors movie the characters successfully killed a graboid by having it swallow homemade dynamite. The second graboid (nicknamed "Stumpy" by Val) had apparently noticed this trap and simply regurgitated the dynamite. Other examples are when the characters escaped on a bulldozer which was too big to be toppled (weighing 30 tons) or undermined (it could drive away before the graboids had a chance to dig away enough of the dirt under it), the creatures dug a trap in its path.

Life Cycle
Fully grown graboids die while giving birth to up to three live shriekers, which seem to chew their way out from the inside. These develop into ass-blasters after shedding their skin. A graboid seems to live for about nine months before transformation, given the information in the film.