Witches’ Butter

Overview

Witches’ Butter (Exidia glandulosa, also known as black witches’ butter or black jelly roll) is one of the most bizarre, biologically resilient, and historically fascinating jelly fungi in the Northern Hemisphere. Belonging to the family Auriculariaceae, this unmistakable saprotrophic fungus forms glistening, convoluted, rubbery black gelatinous masses that erupt from the bark of decaying oak and beech deadwood following autumn and winter rains.

Ecologically, witches’ butter is an essential primary wood decomposer and moisture regulator in temperate broadleaf forest ecosystems. Specializing in dead deciduous branches, its mycelium produces specialized lignin-degrading enzymes that initiate white rot, breaking down tough structural tree fibers and paving the way for secondary decomposers. In European folklore, its sudden, eerie appearance overnight on rotting deadwood was darkly attributed to the nocturnal mischief of witches who buttered the logs with malevolent spells.

Biology and Physical Characteristics

Exidia glandulosa possesses a sensational, shape-shifting gelatinous morphology. When wet following heavy rainfall, its fruit bodies swell into glossy, pitch-black to dark purplish-black, rubbery, brain-like or convoluted lobed masses with a soft, slippery, jelly-like consistency. The outer surface of the lobes is studded with tiny, scattered, pimple-like glandular papillae (warts) that are visible under a hand lens, giving the species its specific epithet *glandulosa*. Beneath the surface, the fungal tissue is composed of specialized branched hyphae embedded in an elastic, water-absorbing gelatinous matrix. Microscopic basidia are longitudinally septate (divided into four chambers like a cloverleaf), bearing curved, sausage-shaped (allantoid), hyaline spores. The crowning physiological marvel of the fungus is anhydrobiosis: during dry, sunny weather, the swollen jelly loses up to ninety percent of its water volume, shriveling into a razor-thin, hard, brittle black crust resembling dried asphalt, completely pausing its metabolism until the next rainstorm rehydrates it back to life.

Behavior and Ecology

Witches’ butter fruits predominantly from late autumn through winter and early spring (October to April), thriving during cold, damp periods when conventional mushrooms have decayed. It emerges through the lenticels and cracks of dead, bark-covered oak (*Quercus*), beech (*Fagus*), and hazel (*Corylus*) branches. Unlike ephemeral mushrooms that rot in a few days, *Exidia glandulosa* fruiting bodies are remarkably perennial: they can endure dozens of freeze-thaw and wet-dry cycles over several months, drying down to a flat black smear during dry spells and swelling instantly back into glistening black jelly within hours of rainfall, continuously releasing clouds of spores whenever moisture is present. While non-toxic, it has no culinary value, possessing a rubbery, tasteless gelatinous texture that makes it strictly a marvel of wild nature.

Conservation and Human Impact

Exidia glandulosa is evaluated as secure and Least Concern across its native global range, appearing abundantly in ancient woodlands and managed timber forests throughout Europe and North America. Because it depends on fallen dead branches that retain their bark, excessive forest ‘tidying’—the practice of removing fallen deadwood and brush piles from parks and woods—can eliminate its vital substrate. Retaining deadwood branches on the forest floor directly preserves the diverse community of native saprotrophic jelly fungi.

Interesting Factoid

Witches’ Butter is virtually immortal against drought: in dry weather it shrivels down into a hard, paper-thin, crispy black crust that looks like dried tar, but as soon as a single drop of rain hits it, it miraculously rehydrates and swells back into a shiny, squishy black jelly within hours.