Season 1: Episode 4- The Graboids (Tremors & Tremors II- 1990/1996)

We examine the entire length and girth of the Graboids, from 1990’s incredibly frightening Tremors. Adam fantasises over Kevin Bacon’s footsteps, Sam abuses time travel, and Dave’s audio is garbage and it’s all his fault.

Movie History – 4:59
Movie Any Good – 17:26
Graboid Physiology – 21:00
Graboid Ecology – 49:23
The Graboids vs. Kevin Bacon from Footloose – 1:16:01

Film: Tremors [1990]
Production Company: Stampede Entertainment
Distributed By: Universal Pictures
Monster: Graboid
Featuring: Sam, Adam, David
Rating: Mature (for some offensive language and adult themes)



Graboid- Physio1
Universal Pictures, 1990


Promotional material once hosted on the Sci-Fi Channel discussed that the graboids were in the he Sepioida order in the cephalopod class of mollusks. The fifth tremors film also discussed that the Graboids were likely evolved from some ancestor similar to a cuttlefish. We will try to build this into our discussion.


As is needed every week, we need to have a rough idea of approximately how heavy the Graboids would be. By using the square cube law and applying it to a number of comparable species whose roles we will discuss later. In the films, an adult graboid is estimated to be about 9.1 metres in length and approximately 20 tons.

Black Mamba (fastest snake)

  • Length (average)= 8.2 feet (2.5 metres)
  • Weight (Average)= 1.6 kg (3.5 lb)
  • Difference In Length= 3.64 times
  • Graboid Weight=  (3.64^3)(1.6)= 77 kg (0.08 tons)

Sepia apama (largest cuttlefish)

  • Length= 0.5 m (20 in)
  • Weight= 10.5 kg (23 lb)
  • Difference in Length= 18.2 times
  • Graboid Weight= (18.2^3)(10.5)= 63210 kg (69 tons)


  • Length= 14 in (35 cm or 0.32 m)
  • Weight= 0.39 oz (11.2 g or 0.0112)
  • Difference in Length= 28 times
  • Graboid Weight= (28^3)(0.01)= 220 kg (0.24 tons)


  • Average White Rhino Mass= 2400 kg
  • Average White Rhino Length= 4 metres
  • Difference in Length= 2.3 times
  • Graboid Weight= (2.3^3)(2400 kg)= 29200 kg (32 tons)

Final Thoughts- Total Mass
The total mass of the graboid as estimated by others is far too heave. It is unlikely that a 20 ton animal would be able to move through the loose soil in the manner seen within the films. Instead I would estimate that the graboids’ weight would be closer to that of an average pickup truck. This is because we see the graboid easily resisting the forces of a truck and being able to bury a truck in the ground. In an ideal world the weight would be even more reduced and closer to that predicted for a graboid sized rhino so that they could move at a more representative speed. I am comfortable placing their mass at a maximum of 2.5 tons and a minimum of 300 kg.


Graboid Skin
The graboids skin appears to be composed in a similar way to a rhino, with a thick hard leathery exterior. This is likely a developed adaptation to survive in desert conditions, offer protection, and conserve water. A rhino’s skin is 1.5 – 5 centimetres thick and is formed from layers of collagen.

Graboid Spikes
In the films, it is repeatedly noted that rigid spikes cover the surface of the graboid. These spikes are believed to be used to help the graboid move through the dirt. On observation, I also think that the spikes aid the graboid in detection of vibrations through its surroundings. It is believe that these spikes work similar to a worms setae.

One of the mechanisms that allow worms to move through the dirt is by employing a series of hair or setae that are connected to each worm segment and help them to bind in the dirt. Worms usually have more than 100 segments with approximately 8 setae attached to each. The setae also have mechoreceptos attached to them in the skin that help the worms to sense vibrations in their environment and surface in the event of rain. It is believe that the graboids could employ a similar mechanism as the worm. However the spike would need to be far greater in number, the graboid would need to move more like a snake than a worm, and the spikes would need to have a complex muscular system that would allow them rise and fall at appropriate times to grip the ear as the graboid moved.

Final Thoughts- Integument
The graboids would likely possess a hard leathery exterior similar to what is seen in a rhino, with thick sheets of collagen built in a lattice structure. This tough exterior would provide needed protection for moving rapidly through the dirt and help to retain water and prevent dehydration in a desert environment. The rigid spikes running across the body could be used to help the graboids move as discussed in the film. The would most likely be composed of hard keratinized material like a pangolin’s scales or a rhino’s horn.


In the film, one of the passing geologists discusses that the graboids’ beak is composed of pure magnesium, and along with secreted acid, helps the monster to move through the dirt. There is no precedent for this type of physiological adaptation in nature, and it would make no sense to build the beak in this fashion. Instead it is more likely that the Graboids would have a beak more similar to that seen in a cephalopod. In a presentation by the science channel, a group of writes discussed that they believed the graboids had evolved from a cephalopod species similar to a cuttlefish. This would make sense for other reasons as discussed in the ecology and other physiology mechanisms. From the perspective of the beak, it would fit that the graboid would build its’ beak like an other cephalopods with two parts composed primarily of chitin and cross-linked proteins.


In the films, it is repeatedly discussed that graboids are an incredibly old species with almost no record of them existing within the fossil record. The theory that graboids might be evolved from cephalopods fits with their lack of fossils. Cephalopod skeletons are composed of Aragonite, a calcium carbonate substance that does not fossilize well. If the graboids had made their skeleton from a similar substance, it is reasonable to believe that they would not be leaving many traces behind for archeologists to find them.

The skeleton of the graboid would need to be strong but not too heavy. An aragonite skeleton is very durable (cuttlefish can survive depths of ~600 metres) but also light allowing for fast movement. Their skeleton is chambered and gas-filled for buoyancy control. It is also built at a microscopic level in a pillared structures that give the skeleton its strength.

In order to move through the dirt at the speeds seen in the film, the graboid would need to build the skeleton and muscular system similar to that of a snake. Snakes have hundreds of vertebrae and skin that are crucial to their locomotion. On their skin that have ventral scales that connect and directly correspond to the number of ribs. When moving, the scales are used in sequence with the contraction of the skin and movement of the ribs to allow snakes to slither rapidly across the ground. The bottom edges of the ventral scales function like the tread on a tire, gripping the surface and propelling the snake forward.

Skeletal- Final Thoughts
The Graboids would likely possess an internal skeleton similar to that of a snake, but composed of Aragonite. Their bones would not fossilize well after death, explaining their absence in the fossil record. The skeleton would be chambered and gas filled, allowing for strength but also decreased weight to help with movement through the soil quickly and without sinking.


Within the film, the Graboids are seen to have orange blood. In nature, the only thing that produces orange blood is an infection or a parasitic infection like Trichomoniasis. I would like to propose that the graboids might suffer from infections (symbiotic or opportunistic) due to their presence in the earth. These infections could explain the blood color and the incredibly poor smell that is always associated with their presence.


General Movement
In order for the Graboid to move at the speeds seen during the film, they would not be able to have a locomotion system like that of a worm. Large earthworm can move up to 73 metres per hour (0.005 mph) at their maximum velocity. Earthworms have no skeleton or other rigid structures that interfere with their movement. Circular muscles around each segments and longitudinal muscles running along the length of their body work with the setae or small bristles coming from their skin. The earthworm uses its setae to anchor the body in the soil and pull itself along.

In order to move at a reasonable velocity, the graboids would need to adopt a movement pattern more similar to that seen in a snake. Snakes employ a variety of movement patterns to achieve locomotion but the one that would work best within the soil would be the serpentine or s-shaped pattern. Starting at the neck, a snake contracts its muscles, thrusting its body from side to side, creating a series of curves. On land, a snake usually finds resistance points in the surface such as rocks, branches or dents and uses its scales to push on the points all at once, thrusting the snake forward. The Black Mamba is the fastest land snake in the world and able to reach speeds in excess of 12 miles per hour (20kph) using this movement pattern. Two of the key muscles responsible for this extend from the ribs (costo) to the skin (cutaneous) giving them their name costocutaneous. One set of muscles pulls the skin forward and then it gets anchored in place as the opposite set of muscles pulls. This strategy was originally evolve for movement underground as snakes evolved from burrowing ancestors.

Mouth Tentacles
The graboids in the film posses a cluster of tentacle-like appendages that emerge from the throat. These tentacles appear to terminate in prehensile “mouths” capable of grabbing prey and pulling them down the monster’s throat. Each tentacles appears to be approximately 3 metres in length.

Cuttlefish have tentacles of their own that extend just cranial to their oral cavity. These tentacles help them to catch prey. At the end of these tentacles are suckers that have a “taste-by-touch” sensor that allows them to discriminate among objects and water currents that they contact. We believe that the graboid tentacles likely have a similar system as it is described in Tremors 2 that the Shriekers use their tentacles/tongues to “taste” objects and distinguish what is edible. Some species of cuttlefish also have venoms attached to their tentacles allowing them incapacitate their victims.

Final Thoughts- Musculature
The graboids would most likely need to employ movement mechanism similar to what is seen in a snake. Movement through the dirt would only be possible in the semi-loose soil found near the surface in desert environments. Coordination of muscles connected between the ribs and skin would allow for rapid movement. Instead of scales being used for grip, the graboids would use the spikes connected to their skin to help with traction. Speeds of 15-20 mph might not be possible (as reported in the film) but up to 10 mph could be feasible (humans run an average of 10-15 mph).

The graboid tentacles would most likely serve as adaptation from their suggested evolutionary connection to cuttlefish. These tentacles could have touch-to-taste sensors to allow them to distinguish edible from non edible. The prehensile ends of the tentacles would help in grasping food to draw in and might also have venom capabilities to help immobilize their prey, explaining why some victims in the film do not appear to struggle much during ingestion.


The incredible size of the graboids, will require that they have some for of an internalized respiratory organ. Unlike the earthworm, they will be far too large to breathe in air through their skin or through the soil. Having large lungs that fill a decent portion of their body cavity will help with keeping their weight down and combined with pneumatized bones, will allow for easier movement through the soil. Breathing will likely be accomplished similar to a whale. The graboid would likely have a form of a blowhole connected to their dorsal surface. This would allow them to take large breaths when travelling near the surface. I would also permit breathing when consuming food, reduce the risks of obstruction from large meals, and allow for breaths to be taken without having to surface their entire head. They would hold their breath when travelling underground and expel air when they arrived at the surface creating the large plumes of dirt typically seen when the graboids appear in the films.


The graboids in the film appear to be intelligent creatures capable or organization and coordination between members to perform activities like holding humans inside structures or digging traps for large vehicles. Cuttlefish are able to communicate using a wide variety of mechanisms including vibration/locomotion. They are thought to be one of the most intelligent invertebrate species and are capable of problem solving and other complex cognitive functions. The graboids appear to have indistinct pain sensation and seem to struggle to localize where damage is coming from when attacked in the basement with guns in the first film. Recent research into squids and other cephalopods has found that their pain detection is different than many other animals. The research suggests that squids, rather than being able pinpoint the location of a wound, an injured squid may hurt all over.

Final Thoughts- Neurological
The graboids would be fairly smart and capable of simple problem solving. Communication could occur through a variety of mechanisms, but I would like to suggest that they could communicate through vibrations in the dirt or chemical secretions/pheromones into their surroundings (possibly also contributing to their terrible smell). They would seem to have a reduced or indistinct sense of pain/nociception, but the utility of such a mechanism is still unclear.


It is established in the film that the graboids lay eggs. Similar to other species we have discussed previously, it is possible that the graboids would dehydrate their eggs. In desert conditions these eggs could lay dormant until exposure to sufficient water. This might be why the eggs seem to hatch whenever caves are opened and exposed to sufficient air in the water or environment.


The graboids are seen to have incredible abilities to detect vibrations in the ground. Another example of detection systems like this in the wild are found within the earthworm. They have sensory buds/bumps located on their skin that contain cilia or small hairs that extend outside of the buds. When vibrations occur in the environment these hairs move allow the worm to detect it. These sensory buds are arranged in rows around the worms body to allow detection in all 3 directions. They also possess light sensitive cell scattered in their outer skin that permit them to be aware when they reach the surface.

Final Thoughts- Sensory Systems
Although blind, the graboids would likely have photo sensors built into their skin to allow them to detect the surface. The would also likely possess a similar type of skin based mechanoreceptor as seen in earthworms allowing for detection of vibrations in the surroundings.


Graboid- Ecology
Universal Pictures, 1990


Determining the ecology of the graboids was an interesting problem in that there are no organisms like them on the planet. There are an enormous variety of subterranean organisms, but nothing on Earth moves through soil with the speed of a graboid.


Our challenge with the graboids was to figure out what led to an organism evolving to be intelligent, massive, and have tentacles. Thankfully, we found our answer with the cuttlefish, a small cephalopod that is known for its intelligence.

The graboid and cuttlefish share a common ancestor, with some amount of similarity to both of them (tentacles, beak, general form). Some members of the species adapted to live in the loose or wet soil along the shore of water bodies, likely an ocean or sea. Over time, these organisms became better able to survive away from water, with adaptations to avoid desiccation and breathe air. Additionally, the ancestors would have lost their eyes, likely their sense of smell, and the tentacles would have moved from the outside of the body (like those of a cuttlefish) to the inside of the mouth, where they would not only be able to help with prey capture but they would also not interfere with moving through the soil. The massive beaks would be a trait that would be selected for, as it likely helps with moving through the soil and and prey capture. After millions of years, these organisms became so well-adapted to living underground and away from water that they were able to utilize a relatively “empty” ecosystem, that of desert soil.


Graboid life-history is fairly complicated, and for the purpose of this summary we will only be focusing on this stage of the life cycle. Briefly, the graboid bursts and spawns several shriekers, which eventually molt into an ass-blaster, which for all intents and purposes can fly. This flight ability allows the species to disperse far and wide, leading us to ask the question of where have they all been? Why are they only seen in Perfection, Nevada?

To answer that question, we only need to look at the history of the United States. Around the mid 19th century, Americans were spreading west (at the expense of the indigenous people already living there). A huge part of this expansion was building railroads, which was a loud process. Not only did the trains make a lot of noise, but the engineers would level mountains in order to make a path for the rail lines themselves. This noise is likely harmful to the graboids when it is that loud, and they would have learned to avoid this noise.

The Great Plains, where most of the ancestral graboid habitat was, is bordered on both the east and west by a enormous mountain ranges. When these east-west railroads cut through this landscape, it fractured the habitat of the graboids, meaning their once massive ranges were divided and fractured, leading to local extinctions. Over time, increasing human development limited the range size of the graboids more and more, until they were left in the small and isolated box canyon of Perfection, Nevada.


Graboids, like their cuttlefish cousins, are incredibly intelligent animals. In the films they are seen to not only trap their human prey and wait for them, but they also lay traps to capture them. The graboids are mostly seen as independent and solitary organisms, though there is some evidence for coordinated action in the film, as well as better examples in the later films.

In Tremors, we see the graboids trap humans on top of buildings, rocks, and towers. This in and of itself isn’t intelligent, but the fact that they wait around for a day or two (the amount of time it takes a human to die of exposure in those extreme conditions in the desert) shows that they understand some aspects of their prey’s limits. We also see the graboids start knocking down the buildings that the humans are using to stay out of reach, though this is likely random aggression.

One great example of their intelligence is when a graboid (or multiple graboids) lay a trap in the road, ruining the one chance the humans had to get away safely on their tractor. Additionally, they learn very fast. The humans are able to trick one into eating a homemade bomb, killing it from the inside. They try the same trick on another graboid immediately afterward, but this one spits the bomb back at the humans, having already figured out that the bomb was a threat.


Balthasar, Uwe. Aragonite and the fossil record: are we overlooking something? AA(Plymouth University, School of Geography, Earth and Environmental Sciences, Plymouth, United Kingdom EGU General Assembly 2016, held 17-22 April, 2016 in Vienna Austria, id. EPSC2016-13765. 04/2016

Bairati A, Comazzi M, Gioria M. An ultrastructural study of connective tissue in mollusc integument III. Cephalopoda. Tissue Cell. 2003 Jun;35(3):155-68.

Ombor Mitra. Vibration Sensitivity in Earthworms: Surfacing Responses to Seismic Vibrations in Florida and Ontario (2009)


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