Why the Graboids from "Tremors" Totally Would Not Have Worked, and the One Thing They Got Right, Part II

We resume my review of the “graboids,” giant carnivorous worms from the 1990 cult classic “Tremors.” My previous post ended midway through a lengthy diatribe criticizing the flaws in their supposed fossorial lifestyle. I’m not quite finished with the criticism, but I do have a few good words to say about the monsters, and the movie as well. So, without further ado…

"Miss me?"

Problem #3: Internal rumblings

It is established fairly early in the movie that graboids are blind*, and detect and follow their prey via seismic waves (= vibrations) – entirely logical adaptations for a burrowing organism. While this detection is shown to be quite sensitive and spatially precise, it is not very discriminatory. Through the course of the movie, graboids are attracted to not only to prey, but to a hand shovel, pogo stick, tumbler, chest freezer, unmanned riding mower, running water, and possibly a jackhammer. 

*Strangely, later in the movie, the graboids supposedly learn that motor vehicles keep their prey safe, and manage to locate and disable a pickup truck and SUV, even though neither is running at the time….

 

But if this style of prey detection is true, graboids have either extremely bad luck or a terrible sense of direction. Nevada, where the movie takes place, is the third most seismically active state in the nation, just behind Alaska and California (you may have heard about earthquakes in those two…). If you look at the geologic map of Nevada to the top left (from here), you may notice that mountain ranges are arranged in parallel bands with an eerie resemblance to the stretch marks on a pregnant woman’s belly (bottom left; from here). This is not a coincidence – in CliffsNotes®-style plate tectonics, the plate being subducted under the west coast (the one ultimately responsible for the San Andreas Fault) is dragging and stretching the western United States along with it, expanding Nevada to several times its original width. Inherent to this is a lot of seismic activity. Graboids trying to pinpoint the footsteps of a puny human amidst all the seismic background noise is akin to trying to find a buzzing housefly in the middle of a dubstep concert.

Incidentally, the co-option of seismic waves by animals is not limited to science fiction. Several modern organisms are suspected of using seismic waves for communication, probably the most notable being the elephant. Elephants, both Asian and African, appear to generate and detect low-frequency waves for long-distance communication. Some paleontologists have also hypothesized that hadrosaurids (duckbilled dinosaurs) may have participated in similar communications, using their elaborate headgear as resonance chambers.

So what’s the good news?

Fortunately, the producers of “Tremors” did manage to include one impressively accurate feature on the graboids (possible unintentionally, but I’m willing to overlook that). In several scenes, graboids display prominent finger-like or fringe-like lateral projections. I assume these to be the gigantic equivalent of setae: miniature hair-like structures found on many organisms, including our invasive friend the earthworm. In earthworms, these structures are very small – even at the microscopic scale in the image below, you may still believe I’m pulling your leg when I say the structures really are there.

asknature.org/strategy/29204f007bb1d29b7c2f63a580fd7d4d

But they are present, and damned effective. Earthworms use them to “grip” the soil and assist with locomotion – an important trait for a cylindrical, slimy invertebrate. They also help the earthworm resist attempts to remove it from the ground - anyone who has ever tried to pull up earthworm probably learned that even if you have the grip of a professional free-climber, the best you will end up with is half an earthworm. Scale this trait up to a whale-sized worm, and very well-anchored organism would result. In fact, in a scene early in the movie, one of a graboid’s “tongues” manages to clamp onto the axle of a pickup. The pickup is able to get away after flooring the gas, but it only succeeds in pulling the “tongue” out by its base, leaving the rest of the graboid likely in exactly the same position it started, albeit in much pain. 

Unfortunately, the graboids in the movie never fully utilize their extreme stubbornness. Towards the end of the movie, the town’s survivors hatch a plan to escape on a bulldozer – reflecting on the graboids’ previous motor vehicle destruction, one of the characters says something along the lines of “[The bulldozer] weighs more than 30 tons. There's no way they could lift that!” Well, it turns out the graboids wouldn’t need to bother. If setae can allow an earthworm to resist something 100,000 times its size, they sure as hell can allow a graboid to immobilize a bulldozer. One graboid would simply need to bite down on the dozer and hold it place, then patiently wait for the trapped prey to “jump ship” (and the graboids are shown early in the film to do just that).

For the record, I don’t mean to sound too critical of the movie – as I said, it is one of my favorites. It effectively blends horror and comedy, portrayed Reba McEntire and the father from “Family Ties” as survivalist gun nuts, and accurately depicted “bromance” decades before Judd Apatow wasted film on nothing but two hours of hairy, pasty-white men waving their dongs at the camera to bad 80’s pop music. But if the producers or writers had consulted with a biologist (or, apparently, a bored paleontologist), they could have created a rare good science/cult classic combination, and saved the bandwidth needed for these last two blog posts.

Although, considering what most of the internet is used for,
perhaps that's not such a great loss after all...