You know those crisp, freezing mornings where the air bites at your cheeks and the mud under your boots has turned to stone? They are my favourite times to be in the woods.
It was on one of these walks, years ago, that I spotted something strange on a fallen branch. At first glance, I thought it was a piece of sheep’s wool caught on the bark. Or perhaps someone had dropped a tissue that had shredded in the wind.
But when I leaned in close—really close—I realised it was neither. It was ice. But not ice as we know it. It was thousands of silky, individual strands, fine as human hair, curling and twisting like a tuft of white candyfloss sprouting from the wood.
I had found Hair Ice. And if you are lucky enough to spot it this winter, you are witnessing one of nature’s most fleeting and fascinating magic tricks.
A Century-Old Mystery
What I love about Hair Ice is that for a long time, it baffled some of the smartest minds in science.
Back in 1918, Alfred Wegener—the very same scientist who first proposed the theory of Continental Drift—noticed this weird ice while walking in the forest. He had a hunch that it wasn’t just physics; he suspected a fungus was involved.
But it took nearly 100 years for him to be proven right. It wasn’t until 2015 that a team of scientists finally confirmed that Hair Ice is caused by one specific fungus: Exidiopsis effusa.
Without this fungus, you just get normal crusty frost. With it, you get magic.
How the Magic Happens
So, how does a fungus turn ice into hair?
It comes down to a process called “ice segregation.” The fungus is living inside the rotting wood, digesting it. As it breathes, it releases water and complex molecules.
Crucially, these molecules act as a “recrystallization inhibitor”—essentially a biological antifreeze. This prevents the ice crystals from growing large and chunky.
Instead, as the water is pushed out of the wood’s pores, it freezes into a single, incredibly thin filament (about 0.02mm wide).
As more water is pushed out behind it, the hair grows longer and longer, sometimes reaching several inches. It’s like a microscopic pasta machine, churning out icy spaghetti.
The “Goldilocks” Conditions
Finding Hair Ice is a bit of a treasure hunt because the conditions have to be absolutely perfect. It is rare, which makes spotting it feel like a real prize.
Here is your checklist for a Hair Ice hunt:
The Wood: It only grows on dead, rotting wood from broadleaf trees (like Beech or Oak). The wood needs to be moist and devoid of bark.
The Temperature: It needs to be just below freezing (around -1°C to -4°C). If it’s too cold, the water freezes inside the wood. If it’s too warm, it doesn’t freeze at all.
The Air: It needs high humidity.
The Time: This is the most important one. You need to be up early. Hair Ice is incredibly fragile. The moment the winter sun hits it, or the air warms up, it melts and vanishes. By 10 a.m., it is usually gone.
A Photographer’s Dream (and Nightmare)
I’ve spent many mornings lying in damp leaves trying to photograph this stuff. It is beautiful, but tricky.
Because it is pure white, it’s easy to “blow out” the highlights, turning the delicate hairs into a white blob.
- Look for contrast: Try to find a patch that is backlit by the low morning sun, or has a dark background of wet bark or moss.
- Get close: This is macro territory. You need to get right in there to show the individual strands.
- Don’t breathe! Seriously. One warm breath in the wrong direction and your subject will melt before your eyes.
A Fleeting Wonder
There is something poetic about Hair Ice. It takes a perfect alignment of biology (the fungus), physics (the temperature), and chemistry (the inhibitor) to create it. And it exists for just a few hours before returning to the soil.
So, the next time you are out on a freezing morning, don’t just look at the grand views. Look down. Check the rotting sticks in the shadows. You might just find the forest wearing its winter beard.
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