[David]

My wife, who's a huge Dune fan and reads the books at least once a year, gave me a link with this description:

How is spice made?
Spice melange is formed deep beneath the sands of Arrakis, where the fungal excretions of sandworm larva mixes with water to form a mass that eventually explodes to the surface due to the planet’s extreme heat. Collecting the melange is extremely difficult; the explosions are deadly and the material hazardous. It’s collected by a vehicle called a Harvester, which must also avoid the giant sandworms. Aircrafts known as Carryalls lift Harvesters to safety.

The Fremen, however, co-exist with the sandworms in the desert and have learned how to harvest spice manually for their own consumption and use.