Hair ice is one of the more stunning small-scale features of the natural world. Strands of ice are sometimes seen bursting from rotting tree branches, falling into a smooth, often rounded mound, resembling a tribble from Star Trek, or perhaps a sleeping white gerbil or cotton candy. 

The mystery of how hair ice forms has raged for a century, as researchers attempted to piece together how the formations developed. Now, a team of researchers believe they finally understand how hair ice is created. The process is dependent on the actions of fungi that are tolerant of cold conditions. 

The quest to discover how hair ice forms dates back to the final year of the First World War. It was then, in 1918, that Alfred Wegener, best known for his contributions to the understanding of continental drift, first began his investigation into the unusual frozen formations. Even at that early stage in research, Wegener suggested that mycelium, the roots of fungi, could play a critical role in the formation of hair ice. 

Discovery of the processes behind the formation of the delicate structures took so long, in part, due to the nature of the fine hairs. The structures usually only form at night and melt at dawn, and they are only found in northern climates at latitudes between 45 and 55 degrees. They typically form during humid winter nights when the temperature hovers just below freezing. 

"When we saw hair ice for the first time on a forest walk, we were surprised by its beauty. Sparked by curiosity, we started investigating this phenomenon, at first using simple tests, such as letting hair ice melt in our hands until it melted completely," said Christian Mätzler of the Institute of Applied Physics at the University of Bern.

Nine decades after hair ice was first formally described by Wegener, a retired professor named Gerhart Wagner found the formations would not develop on wood that had been exposed to fungicide or scalding water. However, this study did not reveal which species was responsible for the development of the structures. 

A team of investigators from Germany and Switzerland set out to determine which variety of fungus created the delicate frozen strands. They found that Exidiopsis effusa was present in every piece of wood tested that formed hair ice. 

Future research will be aimed at describing the formation of the fine structures in even greater detail. 

"I would like to let people realize that science can be unforgettably beautiful without any need for relevance for things that matter in human needs," Mätzler said. 

Analysis of how hair ice forms is profiled in the journal Biogeosciences.