The man stood at the top of a large sand dune on a desert planet. It had taken almost six days to get to the survey post, and he was barely able to stand up straight. Even with careful preparation, the heat was so relentless it would wear you down until you moved like an automaton. The only thing keeping him alive was the specialized suit he wore that could recycle the moisture seeping out of his pores. Out here, water was not even a dream. He was observing the antennae nestled between the dunes that he had been tasked with repairing, when suddenly the sand shifted underneath it. At first he thought he was hallucinating. A wide hole emerged from the sand under the antennae, glistening spokes within it. The hole was three times the size of the 20 metre tall machine. Within minutes, the entire setup disappeared into the hole, with sparks flying and the grating sound of crunching metal filling the air. The man abandoned his task without a second thought. There were likey more sandworms on the way, and that worm that had devoured the antennae: that was one of the small ones.
Giant sandworms appear in all sorts of deserts. They resemble segmented worms, the type you would find in a typical garden, but their segments are composed of nearly indestructible armor. They are typically a dull, mottled brown colour, but there have been some reports of more unusually coloured purple worms. Their mouths are comprised of three-segments which peel back to expose an impressive array of razor sharp teeth that extend back into the body across in many rows. The teeth are as sharp as diamond and have evolved to efficiently rasp rocks and sand. As such, these monstrous worms can burrow through the ground extremely fast. You might sometimes see a massive sandwave, like a moving mountain, following the path of the worm when its head crests the surface. The largest possible size and age of a sandworm is unknown. Their unique diet of sand and adaptation with the desert ecology removes almost all constraints on their growth. In a smaller desert, such as the Gobi desert on Earth, you might expect a mature sandworm to reach 40 - 50 metres in length. But in a massive, ancient desert, a desert that spans an entire planet, a sandworm could be thousands of years old and its body stretch for leagues.
A sandworm is incredibly dangerous. As dangerous as the desert itself. They can sense even the slightest vibrations on the ground. Walking through a desert with sandworms is certain death for travellers. Given their size, speed, and indestructibility, you might think the common sense adventurer would avoid their territory completely. And yet, the stories tell us that, like the dragons, sandworms are often the guardians of a valuable treasure. In one story, a sandworm swallowed an enchanted sword. Who knows what other artifacts could lurk within the bellies of these ancient devourers? In another story, the sandworms produced a powerful drug that granted those who ingested it the power to see the future and travel to the furthest reaches of the galaxy. In that story, the sandworms were seen as the eternal agents of God.