tl;dr: Glacier mice are moss balls found on glaciers worldwide that host micro-ecosystems of nematodes, springtails, and tardigrades, persisting for six years or more. They exhibit puzzling coordinated herd-like movement across ice (~2.5 cm/day), rolling and rotating rather than sliding, likely driven by differential melting where the dark moss absorbs sunlight and creates depressions it rolls into. First described in 1950 by Icelandic meteorologist Jón Eyþórsson, the exact preconditions for their formation remain unknown.