Among the many unusual form’s fungi can take, few stand out quite like Tremella mesenterica, also known as Witches’ Butter. Bright yellow, gelatinous, and often appearing suddenly after it rains. Those encountering it without explanation believed it was left behind mysteriously rather than growing from the trees.
Its appearance alone has long-invited explanation.
In a landscape where unexplained illness or misfortune was often attributed to witchcraft or unseen forces, unusual growths in the forest were rarely seen as something positive or beneficial.
In parts of Britain and Northern Europe, this fungus became known as “Witches’ Butter” or “Witch’s Jelly.” According to folklore recorded in works like The Encyclopedia of Superstitions (1961), such strange yellow substances found on wood were believed to be the residue of a witch’s spell, a deliberate curse, or a trace of hidden activity in the night.
One belief held that witches would “cast” this material onto trees or branches, leaving it behind as a sign of their presence.
If the fungus was seen growing from an individuals doorway, the home was considered cursed.
In parts of Scandinavia, strange yellow growths in the forest were not always seen as natural. They were sometimes described as “butter” or “bile” left behind by the Devil, or as remnants of the work of “troll cats”, creatures believed to steal butter and carry it back to witches.
Because it was associated with curses or witchcraft, people sometimes attempted to destroy or remove the fungus.
Folklore collections note that burning or removing “Witches’ Butter” was thought to counter the spell, protect the land, or disrupt the unseen force.
Unlike some natural signs that were avoided, this substance was sometimes actively destroyed, suggesting it was believed to carry intent rather than simply exist.
These actions reflect a broader pattern in European folk belief, where unusual natural forms, especially those that appeared suddenly, were treated as intentional rather than a natural process.
Like many fungal stories, the explanation came not from understanding, but from observation. Something appeared suddenly, changed with moisture, and seemed to have no clear origin.
Unlike the familiar cap-and-stem shape of most mushrooms, Tremella mesenterica exists as a jelly-like mass, made up of folded, irregular lobes. When wet, it swells into a soft, almost luminous structure. When dry, it shrinks into a hardened, nearly invisible form, only to inflate again with rain.
This ability to disappear and reappear likely contributed to its association with something hidden or supernatural.
Despite its strange appearance, Witches’ Butter is part of a complex ecological process.
Rather than feeding directly on wood, it is parasitic on other fungi, particularly species that inhabit decaying branches. It exists within an already active natural system.
What might look like a sudden, isolated growth is actually part of a much larger, unseen interaction.
Witches’ Butter is a perfect example of how fungi have shaped human imagination.
Before we understood moisture cycles, parasitic relationships, or fungal life cycles, organisms like this demanded explanation. What we now recognize as biology was once interpreted as intention.
And even now, knowing what it is doesn’t entirely remove the feeling that it doesn’t quite belong.
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