Deep in the forests of Switzerland and Germany, something strange is going on. Wispy ice that resembles candy floss has been growing on rotten wood in certain conditions, leaving scientists stumped (sorry) as to what is causing it.

But now a team of researchers think that they have an answer, identifying a fungus called Exidiopsis effusa that seems to be the final ingredient. So-called “hair ice” only grows when the humidity is extremely high, approaching 100%, and the temperature is slightly below 0°C (32°F). Without the fungus, though, the ice will form just as a crust; the fungus is key to it growing into thin hairs. The research is published in Biogeosciences.

“Hair ice is a way for the wood to get rid of water,” coauthor on the study Christian Mätzler, from the University of Bern, told IFLScience. “When wood lies on the ground it gets water from the rain and soil moisture. When it freezes the water inside [the wood] stays as a liquid, but it starts to freeze on the outside, the surface of the wood.”

Hair ice, first discovered by geologist Alfred Wegener in 1918, is remarkable, in that it can keep its wispy shape for many hours. “It may grow one night, and then continue the following night when it’s cool again,” said Mätzler. The phenomenon was found in Switzerland and Germany, but it can be seen in other forests with similar conditions.

^{Above is a time-lapse of hair ice growing in Switzerland.} 

As the ice grows on the outside it dehydrates the wood, which also protects the fungus inside from damage. And, for some unknown reason, this fungus then causes the ice to form in wisps. Mätzler said he didn’t know the exact science behind it, saying that “it is just a special idea of nature,” although recrystallization is thought to play a part.

A coauthor on the paper, Diana Hofmann from the Institute of Bio- and Geosciences in Germany, though, thinks that complex organic compounds called lignin and tannin may be at work. “These components may be the ones preventing the formation of large ice crystals at the wood surface,” she said in a statement.

But “the most surprising thing” was its shape, which can be 10cm (four inches) or more in length, with a diameter of 0.01mm (0.0004 inches), a ratio of one to 10,000. “This is extraordinary,” said Mätzler. “There are not many such elements that have this ratio.”

Is the research important? Well, not really, according to Mätzler. But it is an interesting phenomenon, and certainly one that will have people interested.

“Really, I don’t think it’s relevant for anything for mankind,” he said, “but it’s very nice to see this phenomenon just happen. It’s just a pleasure to me, to work with this without any need for relevance. That’s my conclusion.”