What do the sandworms eat?
A few desert mice won’t sustain such massive behemoths. Nor do they likely get to eat very many humans—and in any event did not evolve with humans present.
shareI looked into it, because I was curious too. Turns out they eat what is called "Sand Plankton," microscopic organisms that live in the sand and feed off of Spice. They also eat sand, and bits of rock deep under the sand's surface (the sands of Dune are miles deep), and occasionally some small animals, but mostly Sand Plankton. They can eat just about anything, but humans aren't technically on the menu. In fact, humans might be considered a source of a stomachache for Sand Worms, because water is poisonous to them, and humans are 60% water. They only go after humans because of the vibrations they make when doing activities on the sand's surface (such as running or operating machinery), mistaking them for food.
shareVery interesting. But that last part is a bit of a problem, because microscopic plankton wouldn’t make vibrations on top of the sand.
shareThat's not the point. The Sand Krill are usually found everywhere in the sand, and the sandworms must travel long distances, swallowing tons of sand and pooping out spice everywhere they go before they are fully fed, and even then, they can put up with an environment like that. Prey they catch on the surface is just some rare treat, rather than their normal meal.
shareBut my point is, why are they so attuned to thumping on the surface when they didn’t evolve with large surface animals as prey?
shareI think, like many desert creatures, earthly or alien, they are opportunists when it comes to food. While it's true that humans [and spice harvesters, and other things on the Arakeen surface] aren't usually part of the sandworms' diet, they often have to go for months not being able to eat, and if there's some kind of creature or machine on the sands' surface they can chomp on, they'll go for it, even if it isn't really good for them. These worms are tough too. Rarely do they suffer much for the unusual food they eat.
I have yet to hear anyone detonate a bomb inside them in any of the Dune stories, but there's always a first time ;)
Like asom said below, their lifestyle and setting are vaguely similar to baleen whales in earth's oceans, just in oceans of sand.
Think whales
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