Planet Earth - Glacier mice: Mysterious moss balls rolling across polar ice

On certain glaciers around the world, mosses gather into spherical colonies known as glacier mice. These peculiar balls harbor miniature ecosystems, providing shelter to nematode worms, springtails, and water bears. They have been documented in varied locations, including Iceland, Alaska, Svalbard, Uganda, and sub-Antarctic islands. Most remarkably, glacier mice do not merely sit in place. They roll across the ice in coordinated, herd-like motions that scientists have found cannot be explained entirely by wind patterns or downhill slope.

Source: Wikipedia