The emperor’s troops, blades wielded, were staring up at a tremendous dust cloud. For a moment, there was just wind, punctuated by silence. And suddenly, there they were: elephantine sandworms, with apocalyptic maws, effortlessly piercing the veil. Jaws dropped—both in the cinema, and on screen—just as the leviathans, adorned with Fremen fighters, careened into the sands of Arrakis.

Whatever your overall opinion of the movies Dune: Part One and the just-released Part Two, the sandworms, the ferocious, fictional animals of that desert-smothered world, are undeniably impressive. Credit goes not only to Frank Herbert, the late author of most of the book series on which these films are based, but to director Denis Villeneuve and his team of creatives, who brought these primaeval beasts to life on screen. They are a thundering presence that somehow feels real, rather than something dreamed up in the minds of artists.

Of course, these sandworms aren’t real—but that they seem so authentic made me wonder if, in fact, elements of them could be found in nature. In some ways, they are unfeasible animals. But in other, more surprising ways, they aren’t as mythical as you may believe.

Fear is the mind-killer, size is the worm-stopper

Despite their unyielding fearsomeness, the Fremen don’t regard the sandworms as monsters, but rather something more benevolent, omnipotent, and almost deific. They refer to them as Shai-Hulud–varyingly translated as “the eternal thing” or “grandfather of the desert.” Crucially, a biproduct of the sandworms’ biology is spice—a multipurpose substance that boosts longevity in the Fremen while allowing navigators to plot safe passage between the stars. And the Fremen frequently make use of these gloriously gigantic worms as forms of transport and, when the need arises, defence. 

Scientifically speaking, the impressive size of these sandworms may be their most glaring problem. They can grow up to 1,300 feet long, which is twice as long as Seattle’s Space Needle is tall. That means they would be so inordinately massive that they would, under Earth-like gravity, not only struggle to move at impressive speeds—they would also be catastrophically pancaked. “It’s just kind of hard to imagine them generating enough energy to move, and to not be crushed under their own weight,” says Michael Werner, a biologist and worm expert at the University of Utah.

Their size also presents other issues. Presumably, like many of Earth’s organisms, their tissues require oxygen to survive. Worms lack lungs; instead, they absorb oxygen from their skin. That oxygen needs to diffuse to all the relevant organs and cells, but that would be problematic for a considerably larger and chunkier worm.

“It’s just kind of hard to imagine them generating enough energy to move, and to not be crushed under their own weight.”

However, in Dune: Part Two, small orifices of some description can be seen beneath the scales of the worms when they are pulled up by hooks. Perhaps these worms, then, do have some sort of lung-based respiratory system, and can store up oxygen in internal fleshy caches. They may have other helpful adaptations. Emma Sherlock, a curator and worm expert at London’s Natural History Museum, explains that some worms—like Megascolides australis, which can be found in parts of Australia—have high amounts of oxygen-binding hemoglobin in their blood, which helps them survive the low-oxygen levels below ground.

Drowning in endless sand

Another major issue is the infamous lack of water on Arrakis. It’s so scarce that the indigenous Fremen drink their own tears, wear specialised suits that recycle all their lost bodily fluids, and harvest internal water from the bodies of recently killed comrades or not-quite-dead-yet enemies.

Earthworms require water to live. Without it, they dehydrate and shrivel up into crusty husks. “In fact, the desert is the only place earthworms can’t survive,” says Sherlock. You find wriggly worms in ice-riddled environments, but not in hyperarid deserts. Unless the sandworms of Arrakis have been secretly moisturising themselves in underground aquifers—not an impossibility, to be fair—then they would have dried up long ago.

A sparse diet of spice-y food

Water isn’t the only scarcity on this forsaken world. The sandworms are seen to consume pretty much anything that rhythmically thrums in their territory, from the spice harvester machines to the Imperial Sardaukar and the brutish Harkonnen troops. But to support their prodigious size and prolific voyages through the sand, they would have to consume far more calories than those hors d’oeuvres. They may occasionally feast on deep-rooted plants, or even one another—but that can’t be their only option, or they would soon become extinct.

Their size is problematic. But, rather wonderfully, it seems like everything else about them is perfectly reasonable.

“Nematodes, a group of worms known as the round worms, can enter an alternative developmental stage called the dauer stage upon unfavourable or harsh conditions where they are surviving on no food for a long period of time,” says Anna Allen, a developmental biologist and program director at the U.S. National Science Foundation. They can do this for several reasons, including when there is a lack of food. The sandworms may do something similar—existing in a stasis mode until they detect nearby prey.

Either way, their size is problematic. But, rather wonderfully, it seems like everything else about them is perfectly reasonable.

Consider their terrifying, Lovecraftian maws. Instead of teeth, they are filled with long spikes, possibly hairs, that act less like chomping teeth and more like filtration systems. Indeed, that’s exactly what the artists behind the movies intended. In a behind-the-scenes video, the teeth are labelled ‘baleen’, as in baleen whales, real-life marine mammals that have tough but flexible keratin hairs inside their mouths that filter their tiny fishy prey from the inflow of seawater. It isn’t clear why the sandworms need this sort of filtration—they seem to happily swallow plenty of sand along with their snacks. But hey, maybe the zoologist on Arrakis that could explain this in more detail was unwittingly gobbled up by one of their subjects.

Psychoactive worm water

In Dune: Part Two, a Fremen is shown neutralising a juvenile sandworm in a water-filled basin, before sticking a syringe down their gullets and extracting a blue liquid. This is a substance known as the Water of Life that, when consumed, either outright kills the imbiber or gives them potent hallucinations—visions of the past, and of the possible future.

“I am not aware of any animals or worms that produce hallucinogenic compounds for humans.”

If you think that sounds silly, the Sonoran desert toad would like a frank word with you. These North American amphibians, which spend most of their time hibernating underground, dislike being threatened. If they get anxious, they excrete toxins that can, if you’re a small-ish animal, induce death. But if you’re a curious and careful human, you can extract an ingredient from these toxins that, when smoked, can trigger a potent psychedelic episode.

Some worms can produce pheromones that can attract other worms toward them. “I am not aware of any animals or worms that produce hallucinogenic compounds for humans,” says Allen. And no known hallucinogen can give you prescience while giving you a highlights reel of your distant past. But the notion of an alien worm producing its own mind-melting unguent doesn’t seem especially bonkers.

The rhythm is gonna get you

The coolest element of the sandworm’s biology may be the way they use sound waves. When we get our first good rendezvous with a sandworm, in Part One, we hear it make a guttural, thumping noise. It’s suggested by the movie’s artists that the percussive, bass-heavy ‘voice’ of the sandworms is why the rhythmic beat of people’s normal walking, and the cyclical thwacking of the Fremen’s gadgets, draws them out of hiding: they recognise it as if something is, unwittingly or not, communicating with them.

Worms may not have ears, but many gravitate toward or flee from sounds that aren’t being made by worms. “A common hypothesis as to why earthworms rise to the surface after it rains is because the rain causes ground vibrations that sound similar to predator vibrations,” says Allen. Burrowing moles, for example, generate tell-tale vibrations that worms can detect. Some do this by using specialised nerve cells. Sound waves hit their skin, causing it to vibrate, which in turn makes any internal fluids wobble about. That triggers those nerve cells, which send out electrical impulses that make the worm move. Perhaps the sandworms have a similar mechanism.

The wriggling wyverns of Arrakis are also able to make the sand around them shift in a preternatural manner. In a production video, the movies’ sound team discuss how they imagined the sandworms would move through the desert, while also trapping their prey. Inspired by quicksand, they decided that the use of directed sound to trigger vibrations at specific frequencies would do the trick. 

If you place a speaker under a pile of sand and blast out some select tunes, you can see this effect for yourself—it really does work, and the impressive biological sound system of the sandworms really makes you believe they could turn the ochre land into a temporary fluid. “That’s very much within the realm of biological possibility,” says Werner.

Wriggly wonders

This underscores what matters most about Dune’s sandworms. We know, almost intuitively, that parts of them are unrealistic—but enough of their design is tangible, and based on things that exist, that they feel real, and are capable of inspiring awe. They are exhilarating creations, ones that, once glimpsed, indelibly lives in our collective imaginations. They are “close enough to something we understand on Earth,” says Werner, which adds substance to their wondrous nature.