The hidden peril under the sands of Arrakis that endangers spice miners is sandworms. These enormous creatures live beneath the desert surface and are drawn to rhythmic vibrations, including the machinery and movement associated with spice harvesting.
In Dune, spice mining is therefore a dangerous operation. Crews use large harvesting machines to collect melange from exposed deposits, while scouts watch for “wormsign,” the rippling or shifting sand that signals an approaching worm. A carryall aircraft is meant to lift the harvester away before the creature arrives, although equipment and workers are often lost.
The Fremen call the sandworms Shai-Hulud and regard them as sacred beings. Their life cycle is also tied to the production of melange: the spice is created through biological processes involving the worms and their earlier sandtrout stage. A common misconception is that the worms deliberately guard spice; in the story, they are territorial animals, and the spice is a by-product of their ecosystem.