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The sandworms of Dune are huge and powerful. But how exactly do they move beneath all that sand? They don't necessarily skim above the surface as they apparently only raise smallish (relative to their diameter) mounds as they move around. What about their physiology allows for such rapid locomotion under (surely) really heavy sand? What happens to the rest of the sand that they dislodge below the surface?

Also, do they always remain close to the surface or do they also "burrow" deep down?

I've only read Dune (the first book) thus far. Please avoid or warn me about spoilers as much as possible.

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    I'd look more into how Sand Trouts dune.wikia.com/wiki/Sandtrout move. The abilities of Sand Trout seems very remarkable and almost supernatural in their movement and transformations. – itchi Dec 17 '12 at 18:44
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    Although that is a good link, be careful, if you haven't read the next two books.. It will spoiler things a bit for you quite a bit; be warned. – K-H-W Dec 17 '12 at 23:17
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It's never explained in detail (at least, not that I recall), but the Worms are segmented, just like the ones you may have encountered in the real world. They move by contracting and expanding their segments, with small spikes (yes, worms really have them) assisting the process. They don't (so far as I recall, although some later books seem to contradict this, and the early books DO mention them eating Sand Plankton) open their mouths and process sand all of the time, the way a worm will tend to do with Dirt, however, they have the advantage of moving thru sand, which is considerably easier to 'push aside', given their size and weight. (The Square-Cube law may make this impossible in RL, for something that size, but given that Frank Herbert never goes into detail, there may be more there than we know of.)

Regardless; they are SciFi Monsters -- some suspension of Disbelief is needed :)

Some worms do stay close to the surface, but some go very deep; there are references in the third book (if I'm remembering correctly) to a worm going deep and sulking after being ridden hard.

Edit - From 'Children of Dune' -

"The worm tired before dawn. Leto slid off its side and watched it dig itself into the dunes, moving slowly in the familiar pattern of the creatures. It would go deep and sulk."

That being said, there is an implied limit to how deep they go; from later in 'Children of Dune',

"It sensed only the sandtrout and would not attack the deep-sand vector of its own kind."

That implies that Sandtrout go deeper than full-blown worms.

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    There may be exotic chemistry going on within the worm, something unknown. I wouldn't even rule out exotic physics... if the sandworms are able to do mass-energy conversion somehow, then Square-Cube goes out the door. – John O Dec 17 '12 at 16:50
  • @JohnO - Quite plausible; that's one of the good things about Herbert not going into too much detail; it leaves the readers (well, those who choose to) to come up with their own explanations. The basic idea (Worms, moving thru sand) is simple enough; how it would work on a different scale requires far less suspension of disbelief than something we don't know about from RL experience. – K-H-W Dec 17 '12 at 19:38
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    Far more fun, tho.. No matter how we picture them moving.. How exactly does riding them work? It they expand and contract (like a true worm), then, uggh.. SQUISH go the Fremen. Wriggling like a snake on the sand? Wow; tossed from size to side, and there's nothing about it in the stories... As near as I can tell, the surface movement is arching like an Inchworm, just to a lesser degree. (See Children of Dune for an example; one of Leto's rides.) – K-H-W Dec 17 '12 at 19:40
  • Shai Hulud have scales covering their bodies. The books describe that the use them during movement in various ways. The scales are probably the equivalent of chaetae of Terran annelids. – SteveED Dec 18 '12 at 1:34
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    @SteveED - Sure, and there is some backup to that in the stories "The worm was a type Fremen called a "growler." It frequently dug in its foreplates while the tail was driving. This produced rumbling sounds and caused part of its body to rise clear of the sand in a moving hump. " (Children of Dune) -- he just never went into great detail, that I recall. – K-H-W Dec 18 '12 at 1:51
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Here's an interesting blog talking about the physics of the worm movement. It ends up saying that a regular sandworm would need to move about 3,000 tons of sand, which would not be physically possible.

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    I might be mis-remembering this, but one of the books said something to the effect that the sandworms pass the sand through their bodies when they move. That blog post mentions it too. Basically, the worms open their mouths and let it flow through and out the other end. Much less sand to move that way. – JohnWinkelman Dec 17 '12 at 16:48
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    Clearly these worms exploit some Quantum Mechanical principle that we are as yet unaware of. :-) – Warren P Dec 17 '12 at 20:50
  • It'll be great if you can incorporate the information from the blog into a more elaborate answer. Very interesting stuff! – coleopterist Dec 18 '12 at 4:21
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There is a lizard that can swim through sand, named, appropriately enough, the sandfish lizard.

It has a very sleek body and pointed head. The body has no bulges or increases in diameter after the head. Once in the sand, the limbs are not used, it moves through the sand with a snaking side-to-side movement. This can be seen in the videos the above linked article contains.

So we already have an example of an animal that can swim through sand. Scaling it up would be difficult, but we have examples of dinosaurs that are very large, so there may be biological models of how this might be possible.

So if you're looking for a scientifically possible explanation, I believe these two pieces of information together might suffice.

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