This episode of Because Science is sponsored by Captive State. How do Dune's Giant Sandworms swim? If I asked you to think about how animals move, you'd probably relexively think of animals galloping across the plains or flying above your head, or gliding underneath the waves. We almost never think about the animals currently moving beneath our feet, and I think that's why the so-called sandworms of pop culture capture our imaginations so much. They are so beyond our experiences. How would they look? How would they move? How would a Giant Sandworm swim? (upbeat electronic music) Oh, we should go, nonrhythmyically though. You can find sandworms everywhere in pop culture, from Beetlejuice, and of course, Tremors, to Final Fantasy and Mass Effect. But the sandworms from the Sci-Fi masterpiece Dune have to be the most famous. Frank Herbert's creations are giant earthworm-like creatures with tremendous moss lined with a stadium of crystalline teeth. Genomically, these worms move through the sand of Iraq as swiftly and forcefully like fictional Leviathans through the water of the oceans. How? What are the biological and physical factors that make movement for a creature like this possible? Let's put on our still suits and figure it out. First of all, those Sci-Fi sandworms are other worldly creatures. Nature has produced a number of animals that can and do swim through sand. These are the so-called subarenacious animals that possess an ability to move long distances through the dunes. These are the animals like the Wedge-snouted Skink and the Black-naped Burrowing Snake. Moving through sand is a lot different though obviously, than moving through water or air, so nature has produced a number of fascinating constraints on how these animals look, act, and move, and we can provide the same constraints to our fictional sandworms to see how they would look, act, and move. Now that's enough recycled sweat and other stuff for today. To make sure we are applying all these constraints correctly, we are gonna work with Dr. Daniel Goldman, a Professor of Physics at the Georgia Institute of Technology. He has published a number of papers on the locomotion of subarenaceous animals, which makes him the perfect Wadebe to lead us on our quest. Oh, we should go. Oh, it smells like yesterday's butt. Uh, the first component of successful sandworm swimming is the material itself, the sand. Sand is what's called a granular material. A material made up of discreet macroscopic particles that interact through forces like friction. The grains of a granular material can be as small as sand grains, or as large as the asteroids in an asteroid belt. What's important for our purposes is that depending on the material's properties, it's internal friction, its moisture content, et cetera, it will be easier or harder to move through. For example, very, very fine desert sand is much easier to move through than dense, course, rocky soil. This means that Dune Sandworms because they're moving through literal dunes have a plausible sand-swimming material. What's much less plausible though are the Graboids from the Tremor series, moving through the very rocky, very dense and obstacle-filled soils of the Sierra Nevada Mountains. The soil there just isn't footloose enough. Whoa ho ho! Having fine loose sand isn't all it takes though. Dr. Goldman's research has uncovered a fascinating and important behavior in subarenacious animals. When they move, they try to make moving through sand as much like moving through water as possible. Under the right conditions, a granular material like sand can act just like a food. For example, if you blow air up through sand at the correct velocity, that sand becomes a so-called fluidized bed, where objects can sink and float and bob around just like they were in water. Dr. Goldman and his team discovered that when sand-swimming animals like the Wedge-snouted Skink move, with their bodies and their movement, they create a tube of more fluid-like sand that they more or less follow with their movement. This makes their movement through the sand much, much easier, and what's really interesting is that this is again, a plausible kind of movement for Dune's Giant Sandworms, because canonically the formation of the spice involves large buildups of air underneath the sand, which can activate the sand even more like a fluid. Aah! Is that? Is that the spice? Oh! The properties of the material are only half the equation though. The sandworms themselves have to be molded physiologically for the best kind of movement through the dunes of Dune. If we were designing a sandworm for efficient sand swimming, what would it look like? Well, let's look at Dune Sandworms a bit more closely. I'll just rhythmically move on the sand here. There we go! This is the most common and accepted depiction of Frank Herbert's Sandworms. Morphologically speaking, based on all the constraints we've gone through so far for real animals, should a sandworm look like this? Should sandworms have spikes? Should they have little appendages all over their bodies? I see dozens of different Sci-Fi depictions, so again, let's turn to Dr. Goldman's research. It suggests that one of the biggest constraints on sand swimming is friction, and so unsurprisingly, evolution has pushed creatures towards becoming as smooth as possible, which means if sandworms did exist, they would most likely not have spikes or appendages all over their body, which leaves us with more or less Frank Herbert's design, and we can get even more specific. So you got any spice on ya? Oh yeah, cool. Yeah, yeah. Cool, cool, cool, cool, cool, be cool. Be cool! Friction wastes energy, and energy is very precious in an extreme environment like a desert, and so this evolutionary pressure has produced some extremely smooth animals. For example, take thee Shovel-nosed Snake an expert sand swimmer, Dr. Goldman and his team measured the coefficient of friction on the bellies of these slither boys and found it to be just point one, possibly the lowest for any known reptile, and so low in fact, that you could just push on this snake with 1/10th of its weight, and it would easily start to sly. This very, very low coefficient of friction allows the snake to move through the sand as efficiently using the least amount of energy possible. Now Dune Sandworms aren't explicitly stated to be very, very smooth, but they do have scales like the Shovel-nosed Snake, so they could be smooth like the snake, or at least optimized for their environment. This one though obviously isn't to scale. There is one more morphological constraint that we can consider, for reasons we will get into in just a bit. It helps when moving through sand biomechanically speaking to be as slender as possible. That is to say for sand swimming, it helps to be much longer than you are wide for this ratio to be very high. The sandworms of Arrakis are enormous, but we can still calculate this ratio. Let me show you. Oh! Canonically, sandworms can mature to be up to 400 meters long, or a quarter of a mile. If I were to start walking from this sandworm sand butt, it would take me the same amount of time to move through the equivalent of, oh no, forget it, too far. Uh! Oh, I guess that worked. The length to width or elongation ratio of most subarenacious reptiles is somewhere between five and 55. Using the numbers that you can find in the first Dune novel, a sandworm's elongation ratio falls between five and 35, which means despite its enormous size, this body type is plausible. Huh! Dune Sandworms may have plausible properties and their stats may stack up, but they won't work as sand swimmers unless they move in the right way. Not like worms at all. While worms, like your typical earthworm do move through granular materials like soil, they don't do so very fast. That's because they move like this, by compressing somebody segments and stretching out others to move through the soil like a dirt slinky, which is what I'm calling them now. Snakes and snakes that swim through sand specifically do something very different. They slither. As they move through the sand, they create a series of undulating waves that press on the sand around them. This in effect creates a net force forward, which propels them through the sand and overcomes forces like friction. Using X-ray imaging, Dr. Goldman and his team have looked at sand swimming snakes and a lizard called the sandfish as they move underneath the sand, and as you can see, using this kind of serpentine motion, they can go surprisingly fast. If Dune Sandworms are to move swiftly in sand, then it's likely that they're gonna employ this kind of motion, and this is where the slenderness ratio that we talked about before makes a big difference. The larger the elongation ratio, the more optimal undulations a subarenacious animal can make. This would theoretically make an animal like a Giant Sandworm or the Shovel-nosed Snake more efficient and sand swimming than the chunkier sandfish, and this is exactly what Dr. Goldman and his team have found. As you can see here, the Shovel-nosed Snake is pushing with many waves on the sand around it, while the sandfish is pushing with only one. More waves means more pushing, which means a longer more slender animal can adapt to a larger range of conditions. If Dune Sandworms are really up to half-a-league long, almost two miles, there is some universe where Dune Sandworms are as efficient as this snake. Finally, sand is heavy, heavier than water, and so more realistic sand swimming sandworms would have to spend most of their time swimming at the surface of sand, and that's because of something called lithostatic pressure. Lithostatic pressure is like hydrostatic pressure, the pressure that you get by going deeper and deeper underwater, except that instead of water, this pressure is from soil and sand and rock. This pressure is ever-pushing on subarenacious animals, and it acts to lift them towards the surface. Yes, even in sand. Everything else about Dune Sandworms has kind of checked out so far, so let's do our due diligence and read a quote from the original Dune, "It appeared to be more than half-a-league long, and the rise of the sand wave at its cresting head was like the approach of a mountain." It sounds like, at least when the sandworms are on the hunt, they move at the surface of the sand, which means taking everything together, these former little makers kind of make sense. Woo! So how do Dune's iconic sandworms actually swim? Well to do so more realistically, they have to move through a granular material like fine desert sand, like a snake that is long and slender with very smooth scales, undulating with optimized waves as they do so. Given the description of the sandworms in Dune, how they act, how they move, what they look like, them realistically sand swimming is surprisingly plausible, which is a much spicier result than I was expecting. Because Science, I'll see you next time. (upbeat electronic music) Thanks again to Captive State for sponsoring today's episode. From the director of Rise of the Planet of the Apes comes Captive State, set in a Chicago neighborhood nearly a decade after an occupation by an extraterrestrial force, Captive State explores the lives on both sides of the conflict, the legislature and the resistance. Ten years later, Gabriel, the catalyst for the resistance rises as their leader, sparking a fire that ignites the war for the world. Watch Captive State in theaters tomorrow. Thank you so much for watching, Jordan, and a huge thank you to Dr. Daniel Goldman, who talked me through his fascinating research, and helped me a lot on this video. If you want to read his fascinating paper on sandfish and slithering sand snakes, you can check it out in the link in the show's description. Also, the second episode of the Science of Mortal Combat is now live. You're gonna want to check it out, and if you have an idea for me about a future episode of this show, follow us here. (loud fascinating music)
