three meters long) sandworms". A small number of these then emerge into maturity as giant sandworms, to whom water is poisonous. A "stunted worm" is a "primitive form... that reaches a length of only about nine meters". Their drowning by the Fremen makes them expel the awareness-spectrum narcotic known as the Water of Life. While sandworms are capable of eating humans, the latter do contain a level of water beyond the preferred tolerances of the worms. They routinely devour melange-harvesting equipment—mistaking the mechanical rhythm for prey—but they seem to derive actual nutrition only from sand plankton and smaller sandworms, and have no actual interest in the spice. Sandworms will also not attack sandtrout. Behavior and function In Dune, the desert of Arrakis is the only known source of the spice melange, the most essential and valuable commodity in the universe. Melange is a geriatric drug that gives the user a longer life span, greater vitality, and heightened awareness. It can also unlock prescience in some subjects, which makes safe and accurate interstellar travel possible. The harvesting of melange is therefore essential, but is also a highly dangerous undertaking due to the presence of sandworms. Rhythmic activity as minimal as normal walking on the desert surface of Arrakis attracts the territorial worms, which are capable of swallowing even the largest mining equipment whole. They are an accepted obstacle to spice mining, as any attempt to exterminate them would be prohibitively expensive, if not entirely futile. Harvesting is done by a gigantic machine called a Harvester, which is carried to and from a spice blow by a larger craft called a Carryall. The Harvester on the ground has four scouting ornithopters patrolling around it watching for wormsign, the motions of sand which indicate that a worm is coming. Melange is collected from the open sand until a worm is close, at which time the Carryall lifts the Harvester to safety. The Fremen, who base their entire industry around the sale of spice and the manufacture of materials out of spice, have learned to co-exist with the sandworms in the desert and harvest the spice manually for their own use and for smuggling off-planet. Due to their size and territorial nature, sandworms can be extremely dangerous, even to Fremen. The worms are attracted to—and maddened by—the presence of Holtzman force fields used as personal defense shields, and as a result these shields are