The sandworm is a native lifeform of the planet Arrakis. It lives in the vast sand dunes that stretch across the surface of the planet, and is a by-product of the same process that creates the Spice Melange.
Sandworms typically stay beneath submerged in the sand, although occasionally they will surface. They are attracted to rhythmic vibrations, including human footsteps, which perturb them and will cause them to attack the source.
Sandworm can grow to a huge size. Specimens up to 400 meters long have been spotted by humans in the deep deserts of Arrakis. They naturally live to a great age, ranging in the thousands of years, unless killed by humans or other sandworms.
In appearance their skin is thick and protective. It is comprised of many scales, each a few feet in size, that overlap to form an armor to protect against sand abrasion. But as the Fremen discovered, prying one or more scales up causes irritation. The sandworm will roll itself until the prone scale is at the highest point from the desert floor, so as to avoid sand getting trapped beneath it. This weakness is used by the Fremen to control the direction and speed of the creature, thus making them a viable method of transporting people.
Internally the sandworm is a massive furnace, producing almost unimaginable heat. The forward end of the creature possesses a huge yawing mouth that can easily consume large ground vehicles, including spice harvesters. A strong flinty, cinnamon smell exudes from the open mouth of the sandworm. The sandworm is highly susceptible to water poisoning.
Creation of Sandworms
The sandworm is created when sandtrout band together after converting water deep beneath the surface of Arrakis into a liquid chemical that the sandworm is capable of digesting without being poisoned. This chemical then erupts up to desert's surface in a pre-spice mass.
The sandtrout that survive this event then coalesce and are metamorphasized into a young sandworm.
Cultural Impact of the Sandworm
Yet to the planet's Fremen population it was a spiritual symbol of their faith, who saw the creatures as physical embodiments of the One God of their original Zensunni religion. Within Fremen culture the sandworm had several additional names, notably Shai-Hulud, which variously means 'Old Man of the Desert', 'Old Father Eternity', and 'Grandfather of the Desert', as well as alluding to its perceived deific qualities.
Young sandworms are also sought by the Fremen for special ceremonies. When poisoned with water, the young sandworm is killed, but not before it chemically alters some of the water and expells it through its mouth. This liquid, known to the Fremen as the Water of Life, is used to induct new Bene Gesserit reverend mothers. The toxic liquid forces the prospective reverend mother to either purify the water or die. During this process dormant genetic memories and other abilities are activated, heralding the creation of a new reverend mother.
After the rise of the Atreides Empire and the propagation of the Arrakis-variant of the Zensunni religion, the reverence paid to the sandworm spread to other worlds. This continued through the rule of Leto Atreides II, in no small part because of his merger with sandtrout to form a hybrid human-sandworm being.
Decline of the Sandworm
The terraforming of Arrakis posed a grave risk to the sandworm, which found life outside the arid desert poisonous. The terraforming reversal process had begun by the end of Leto's reign, and he himself had devolved back into sandtrout at his death. These events saw the sandworm once again thrive on Arrakis for a few thousand years. During Leto II's reign some smaller sandworms were also removed and shipped off with colonizing vessels during the Scattering. The exact success of these samples remains unclear as of the end of 'Chapterhouse: Dune'.
The hostile actions taken by the Honored Matres saw the termination of all life on Arrakis, including the sandworm. But not before their enemies had spirited away at least one more of the creatures, which accompanied them on their escape from the unified Bene Gesserit/Honored Matres organization and into uncharted space.