The sandtrout, in the fictional world of the Dune novels by Frank Herbert, is a small creature that lives under the sands of Arrakis. Also known as the waterstealer, or the little maker. Little more than a membrane like worm, they fuse together around pockets of water. This formation becomes a pre-spice mass, which, after violently exploding up to the surface, becomes a patch of the spice. Each explosion kills sandtrouts by the million, but those who survive encyst and lie dormant under the sand for around six years, to emerge as an infant form of the enormous sand worm.
Fremen children play a game with sandtrout they find near the surface. When taken in hand, the sandtrout will move to form a membrane around the takers hand. It can then be bitten to extract a sweet syrup like substance. If near the sietch, the sandtrout can also be taken back to the deathstills to reclaim its water. This game was what inspired Leto II to encase his entire body with a membrane of sandtrout, thus giving him superhuman abilities, or more philosophically, removing him from the human branch of evolution.