Dune’s sandworms explained: A spoiler-free guide to Shai-Hulud

Walk without rhythm! If you’re only vaguely familiar with the sci-fi world of Dune, you may think it’s just a bonkers story about giant sandworms who live on a desert planet.

Here’s the thing, that assessment is not wrong. Dune is about many things, but to say that it is about sandworms is totally correct. And what’s the deal with these sandworms of Dune? What do they do? Why are people obsessed with them? And most important, how do you ride one? Here’s your spoiler-free guide to the sandworms of Dune.

What are the sandworms in Dune?

The sandworms in Dune are giant animal worms known by their indigenous name as “Shai-Hulud.” To the Fremen, the deep desert dwellers of Arrakis, Shai-Hulud is considered a quasi-diety and sometimes called “Old Man of the Desert.” (When you see the new film, this last designation is important in one particular scene.)

The sandworms are not considered sentient, but they are extremely dangerous. The adults can measure from 20 meters to up to 400 meters. In the new film and early footage, you’ll see a sandworm that can eat an entire spice harvester, but also one that looks like its mouth is the size of four elephants. The official glossary at the back of the first Dune novel gives us the “400 meters” figure for the massive ones, but there are various lengths mentioned in the quasi-non-canon Dune Encylopedia. (There’s also a whole section that book about the reproductive stages of the sandworms if you’re into that kind of thing.)

The sandworms aren’t the only indigenous lifeforms on Arrakis, but they are certainly the most prominent. They’re drawn to rhythmic sounds, which means if you don’t want to attract them, you have to walk through the desert in an erratic, non-rhymic fashion. (This is called “the sand walk,” and it looks silly.) And yes, the banger Fatboy Slim song “Weapon of Choice” does reference this concept with the repeated line “Walk without rhythm/It won’t attract the worm.”

That said, if you want to attract a worm quickly, you can use something called a “thumper,” which is exactly what it sounds like; a device that makes rhythmic thumping.

Why are sandworms important in Dune?

Other than being totally dangerous alien animals, the Shai-Hulud are the one thing that makes mining the Spice Melange super-difficult. In the world of Dune, the fictional substance known as a “spice” does many things, but as a natural resource, it allowed for space travel across star systems to be possible.

Essentially, spice gives the mind the ability to perceive time-space differently, which creates future visions for some characters. (In the movie, you’ll know this when you see it!) But because the worms are always nearby during the spice harvesting (those damn rhymic sounds!), worms are always eating and destroying equipment.

For the Fremen, the teeth of the giant sandworms are sacred. In the books and the new movie, various characters get a “crysknife,” a special weapon made by the Fremen from a single sandworm tooth. These knives are a big deal in Fremen culture, and if anyone who is not a Fremen is given one of these knives, it essentially means that person is very special.

Some crysknives are so fragile that if they’re not close to a human body, they’ll turn to dust. This makes it sound like they’re not powerful, but that’s not the case. Like the sandworms they come from, the crysknives are some of the most deadly items in the world of Dune.

Why do people ride sandworms in Dune?

The short answer is: Because it’s handy! The creatures that are most adept at surviving the deep deserts of Arrakis are the sandworms, and so, the Fremen, sometimes, hitch a ride on the sandworms. If thumpers are used correctly, people can herd sandworms in specific directions. To ride a sandworm, people use something called a “maker hook,” which in Dune: Part One, is something you’ll see at least once.

Without spoiling anything, it's easy to imagine why someone building an army in an alien desert might want to ride and herd super-destructive sandworms. The sandworms can’t be tamed exactly, but that doesn’t mean they’re entirely wild either.

One of the themes of Dune is all about Paul and his allies figuring out how to accept the culture of the Fremen and also use that knowledge to start a revolution. Smack dab in the middle of all that are the sandworms, the greatest danger on Arrakis, but also the secret weapon of Dune.

Dune arrives October 22 in theaters and on HBO Max.