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Glaciers are some of the most forbidding places on Earth, but if there are life-forms that live on volcanoes, why can't there be something crawling in the bitter cold?
Meet Mesenchytraeus solifugus (above and below). These eerie black ice worms spend their entire life deep inside Mount Rainier's Paradise Glacier (as well as other glaciers), but emerge by the billions every summer. Why they bother to come to the surface remains unknown. Not many people are concerned about ice worms, even as global warming slowly melts their habitat, but biologist Scott Hotaling of Washington State University is obsessed with them.
Hotaling has made M. solifugus one of his main research subjects after many, many questions came to his mind when he first saw ice worms wriggling up from their lairs. These squirmy extremophiles and related annelids that live in ice are surrounded by mystery.
“The question of what they are doing outside of summer when we can readily observe them still hasn’t been answered,” Hotaling tells SYFY WIRE. “They might carry on as usual, just under a very deep layer of seasonal snow, or they might go into some kind of diapause during winter.”
Any creature that goes into a diapause experience goes into suspended development after a drastic plunge in its metabolic activity. Its growth and molting hormones also decrease as temperatures and other environmental conditions grow less favorable. This is most commonly seen in insects, especially in the cocoon stage of those that form pupae, but also occurs in some mites, crustaceans, and snails. However, for those worms that are adults, what are they up to?
M. solifugus might be the ice version of earthworms. In the summer, they do what their terrestrial relatives do in the dirt, creeping around and eating whatever bacteria and algae comes up, then excreting it as they go. The surface is teeming with food. Finding out what goes on with them during the winter is not exactly easy since they bury themselves under too much snow for humans to follow. They move using hairlike setae on their undersides. When enough winter snow and ice melts, they are able to wriggle their way through.
What is especially bizarre about M. solifugus is that they can survive freezing temperatures — but not actually being frozen (that honor goes to another ice worm). Not that they enter what is otherwise a deep freeze unprepared. They produce antifreeze-like proteins to stay alive, and ironically, even though they spend most of their lives underground, they have an amazing UV tolerance. The high melanin levels throughout their bodies (which are higher than those of any other worm species) are like built-in sunblock.
“These worms are clearly well-suited to the cold conditions, and their biochemistry must reflect that,” Hotaling says. “They are also able to tolerate the exceptionally high UV and limited availability of nutrients. Ultimately, a mix of behavioral and evolutionary changes contribute to their unique phenotype.”
What may keep these worms going under several dozen feet of snow and ice is the way they metabolize what nutrients they are able to get. They use ATP (adenosine triphosphate) in a different way than most creatures. ATP is the ultimate energy molecule, but the cells of most living things, including humans, are not able to use it as much as temperatures go down. In M. solifagus, the exact opposite happens with a drop in temperature to at least a chilling 21 degrees Fahrenheit, usually lower. The metabolic increase is another factor that keeps them from freezing.
There have not been many genetic studies done on M. solifugus, which are endemic to Alaska and the Pacific Northwest, but it is thought that they probably didn’t always take refuge in glaciers. They may have lived in the ground instead. As glaciers retreated towards the end of the last Ice Age, they brought the worms with them, but the threat of global warming is raising serious concerns about the loss of their habitat.
“Glaciers are melting because global temperatures are on the rise,” Hotaling says. “Primarily reducing our own CO2 (and related emissions) while also supporting policies and initiatives to actively remove CO2 from the atmosphere can help keep ice worms from going extinct.”