We Finally Know How "Glacier Mice" Moss Balls Move In Herd Formation

Carsten ten Brink/Flickr/CC BY-NC-ND 2.0

Researchers have long been baffled by the existence of “glacier mice”, small balls of green moss that appear en masse in the icy landscapes surrounding glaciers, like a low-budget, PG take on The Day of the Triffids. These colonies of moss balls were thought to move randomly but new research published in the journal Polar Biology details how these bizarre fuzzballs actually move at a uniform pace and in the same direction. 

The unusual moss balls were first described in a 1950s research paper in the Journal of Glaciology by an Icelandic researcher who described rolling stones covered in moss gathered from the ground, which he termed “ jökla-mýs" or "glacier mice." The arctic fuzzballs have since become a much-loved phenomenon among glaciologists even though, until now, extremely little was known of where they come from and why they move. 

A team from the University of Idaho set out to uncover the mystery of these moving moss balls in Alaska. They tracked 30 glacier mice by tagging each moss ball with a loop of wire and some beads. They monitored the movement of the moss balls for 54 days in 2009 and returned annually for 3 years. A review of their findings revealed that the movement of the glacier mice was not as random as predicted.

"The whole colony of moss balls, this whole grouping, moves at about the same speeds and in the same directions, those speeds and directions can change over the course of weeks,” Bartholomaus said in an interview with NPR.

"When we visited them all, they were all just sort of moving relatively slowly and initially toward the south. Then they all started to speed up and kind of start to deviate toward the west. And then they slowed down again and progressed even farther to the west."


The coordinated movement of the moss balls surprised the researchers as rather than sporadically distributing due to changes in the wind, it was found the balls actually shifted about an inch a day in formation in a way comparable to groups of wildebeests or flying birds. Sophie Gilbert, a wildlife ecologist at the University of Idaho and another one of the study’s co-authors, explains in the study how this movement enables the entire of the glacier mouse’s surface area to be exposed to the sun. If the glacier mice didn’t “roll” around, the bottom part of the moss ball would die. 

The researchers stress that there’s still much to discover about these bizarre moss ball herds, but their occurrence adds further evidence that glaciers are not quite so sterile as previously believed. Rich communities of bacteria and algae, as well as the perplexing glacier mice are found in these environments, and present an exciting area of investigation for future research. 

The below video, which is not a part of the published study, shows how glaciologists worldwide have come to love these weird green fuzzballs, with the bizarre phenomena having been observed in Alaska, Iceland, Svalbard, and South America.


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