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All right. I didn't know this. Maybe you did. Little balls of bright-green moss sometimes live on glaciers. These moss balls have a nickname - glacier mice. And as NPR's Nell Greenfieldboyce reports, they move around in this mysterious way.
NELL GREENFIELDBOYCE, BYLINE: These green fuzz balls really stand out against the stark, white ice. Tim Bartholomaus is a glaciologist at the University of Idaho. He first saw them while hiking around a glacier in Alaska and was startled.
TIM BARTHOLOMAUS: What the heck is this? They're too obscure to have, you know, textbooks written about them. You know, and so I wasn't anticipating them.
GREENFIELDBOYCE: Unlike the moss you might see in the woods, this moss isn't attached to anything. It's just a ball made of moss, sitting on the ice.
BARTHOLOMAUS: Yeah, soft and squishy and kind of like a sponge of really soft, lush, green moss.
GREENFIELDBOYCE: They're rare, but scientists who've seen them tend to be fond of them. Sophie Gilbert is a wildlife biologist, also at the University of Idaho.
SOPHIE GILBERT: They're so weird and interesting looking. They really do look like little mammals, little mice or chipmunks or rats or something running around on the glacier, although they run in, you know, obviously very slow motion.
GREENFIELDBOYCE: She wanted to understand that motion.
GILBERT: These things must actually roll around, or else that moss on the bottom would die.
GREENFIELDBOYCE: So she and Bartholomaus tagged 30 of these moss balls, sort of like ornithologist tag birds. They tracked each ball's precise location for a couple of months. Bartholomaus thought the balls would roll around randomly.
BARTHOLOMAUS: But what we actually found is that the whole colony of moss balls, this whole grouping moves at about the same speeds and in the same directions. And those speeds and directions can change over the course of weeks.
GREENFIELDBOYCE: In the journal Polar Biology, with Scott Hotaling from Washington State University, they report that the moss balls traveled on average an inch a day. And the balls can live for years. But here's the thing - how they move together like a herd remains a mystery. Bartholomaus says they checked out a bunch of possible explanations - the downhill slope, the prevailing winds, the incoming solar radiation.
BARTHOLOMAUS: And none of them explained the directions that the moss balls were moving. And so we still don't know. We're - I'm still kind of baffled.
GREENFIELDBOYCE: Other scientists find this intriguing. Ruth Mottram is with the Danish Meteorological Institute.
RUTH MOTTRAM: I think that probably, the explanation is somewhere in the physics of the energy and the heat and around the surface of the glacier. But we haven't quite got there yet.
GREENFIELDBOYCE: She recalls seeing moss balls in Iceland.
MOTTRAM: I think they're extremely engaging when you look at them in a great, big mass. It's very hard not to think of Tribbles from "Star Trek" or something like that.
GREENFIELDBOYCE: She says they're just one example of how life can flourish on a harsh glacier. Nell Greenfieldboyce, NPR News.
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