The Pyramid-builder is a strange silicon-based life form native to the deserts of Mars. It's an extremely simple organism, consisting solely of a mouth, a single arm and a stiff tail which it can use to root itself in the desert soil to absorb silicon from the rocks. The only waste it produces is in the form of small bricks, which it arranges in the form of pyramids - hence its name. It's speculated that the creature is immortal and completely mindless, having no goal in life other than to consume silicon and produce pyramids. It reproduces by means of small transparent hollow spheres, light enough to be carried by the Martian wind currents, and which consist solely of a thin silicon shell and reactive gases within. It's believed that these gases react with the soil where it falls to produce newborn Pyramid-builders, but the process is so slow that it's never been properly observed, as it would take thousands of years for the soil components to organize themselves into a new organism.
- "A Martian Odyssey", by Stanley G. Weinbaum (1934) (First appearance)
- "Valley of Dreams", by Stanley G. Weinbaum (1934) (Mentioned only)
- "Tidal Moon", by Stanley G. Weinbaum and Helen Weinbaum (1938) (Mentioned only)