# Foxfire
Foxfire is the faint greenish glow produced by bioluminescent fungi growing in decaying wood, named historically for the luminescent mycelium, mycelial fans, and rhizomorphs (root-like fungal strands that spread and glow) of *Armillaria* honey fungi[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC11766655/). The term refers to the phenomenon rather than to a single species; the same glow is also called fairy fire or glow wood[2](https://blog.mycology.cornell.edu/2010/04/12/this-bark-glows-in-the-dark-bioluminescence-in-mushrooms/). Observations of the glow go back at least to [Aristotle](https://www.edgepedia.org/aristotle), who described a "cold fire" light emanating from the woods, and to [Pliny the Elder](https://www.edgepedia.org/pliny-the-elder), who in the first century described luminescent mushrooms on white wood in olive groves[3](https://www.lib.uchicago.edu/about/news/foxfire-and-fungi-solving-a-2300-year-old-mystery/).
| Key fact | Detail |
|---|---|
| What it is | Bioluminescence of fungi in decaying wood; historically the glow of *Armillaria* mycelium, mycelial fans, and rhizomorphs[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC11766655/) |
| Light color | Green light with maximum intensity in the range 520–530 nm[4](https://doi.org/10.1111%2Fphp.12135) |
| Species count | Known bioluminescent fungi more than doubled in 15 years, from 64 to 132 species[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC11766655/) |
| Lineages | Five lineages of bioluminescent Agaricales: Omphalotaceae (18 species), Physalacriaceae (14), Mycenaceae (96), Lucentipes lineage (3), Cyphellopsidaceae (1)[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC11766655/) |
| Chemistry | Luciferin is 3-hydroxyhispidin (from hispidin); the light emitter is caffeylpyruvic acid, produced via the Caffeic Acid Cycle[5](https://www.mdpi.com/1424-2818/16/9/539) |
| Ecological role | Strong evidence the glow attracts spore-dispersing insects; it may also function as a defense against oxidative stress[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC11766655/) |
| Historical record | Described by Aristotle as "cold fire" and by Pliny the Elder; Scandinavians used luminescent bark for light on winter nights[3](https://www.lib.uchicago.edu/about/news/foxfire-and-fungi-solving-a-2300-year-old-mystery/) • [2](https://blog.mycology.cornell.edu/2010/04/12/this-bark-glows-in-the-dark-bioluminescence-in-mushrooms/) |
## Where the glow comes from
The classic source of foxfire is the vegetative mycelium of wood-decay fungi, above all *Armillaria* species such as the honey fungus *Armillaria mellea*, which colonize rotting wood and roots[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC11766655/). Until recently only the mycelium, mycelial fans, and rhizomorphs of *Armillaria* were reported as luminescent, and the mushroom fruiting bodies themselves were consistently reported as non-luminescent, although light emission could be induced by spraying them with an extract of fungal luciferin[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC11766655/). Two exceptions have since been documented: *Armillaria limonea* from New Zealand and an undetermined species from Brazil form pilei (caps) that show bright luminescence[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC11766655/).
Foxfire is one expression of a broader trait. Across bioluminescent fungi, different parts glow depending on the species: 36 species (29.5 percent of known cases) present only mycelium bioluminescence, 48 species (39.3 percent) present only fruiting-body bioluminescence, and 37 species (30.3 percent) glow in both[5](https://www.mdpi.com/1424-2818/16/9/539). The glow is often faint, sometimes detectable only with a luminometer, though an entire mycelium can emit visible light[6](https://chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/cbic.202400106).
## The chemistry of the glow
Like other bioluminescence, fungal light production is a luciferase-catalyzed oxidation of a substrate called luciferin, producing light without heat[5](https://www.mdpi.com/1424-2818/16/9/539). In fungi the luciferin is 3-hydroxyhispidin, enzymatically derived from hispidin, and the structure was identified in 2015 using the mycelium of the Vietnamese luminous fungus *Neonothopanus nambi*[7](https://pmc.ncbi.nlm.nih.gov/articles/PMC10302135/). The reaction product, and light emitter, was identified in 2017 as caffeylpyruvic acid, a pyruvic acid adduct of caffeic acid; oxidation of the luciferin is proposed to pass through a high-energy endoperoxide intermediate[7](https://pmc.ncbi.nlm.nih.gov/articles/PMC10302135/) • [8](https://pmc.ncbi.nlm.nih.gov/articles/PMC5406138/).
**One shared pathway.** Cross-reactions between extracts of different luminescent species showed light emission, indicating that fungal luciferin and luciferase are common across bioluminescent fungi[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC11766655/). The pathway is now called the Caffeic Acid Cycle (CAC), and it is the only fully encodable eukaryotic bioluminescent system known: only bioluminescent fungi contain the h3h, luz, and cph genes, even though many plants and non-bioluminescent fungi can biosynthesize hispidin[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC11766655/). The pathway has been successfully reconstituted in multiple plant species, producing autoluminescent plants[9](https://www.sciencedirect.com/science/article/pii/S2452223621001267).
## Distribution and diversity
Glowing fungi are found across the globe, though documentation is uneven; the greatest numbers of known species have been recorded in Japan, where 36 have been identified, followed by South America with 30 and North America with 27; Malesia together with South and Southeast Asia accounts for 26, Europe for 23, and [Central America](https://www.edgepedia.org/central-america) for 21; China has 13, [Australasia](https://www.edgepedia.org/australasia) along with [Papua New Guinea](https://www.edgepedia.org/papua-new-guinea) and New Caledonia has 11, Africa has 10, and the Pacific Islands 5.[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC11766655/) Molecular phylogenetic analyses recognize five distinct lineages of bioluminescent Agaricales, and the phenomenon is thought to have originated a single time early in the evolution of that order, with multiple independent losses explaining why many species within the lineages, and the majority of Agaricales overall, do not glow[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC11766655/).
## Why fungi glow
The ecological function is not fully understood, but the best-supported role is attracting nocturnal insects that disperse spores, much as flowers attract pollinators[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC11766655/) • [3](https://www.lib.uchicago.edu/about/news/foxfire-and-fungi-solving-a-2300-year-old-mystery/). A study of the Brazilian species *Neonothopanus gardneri* found that the fungus regulates its bioluminescence through circadian rhythms: levels of luciferin, reductase, and luciferase peak at night, when insects that cannot otherwise locate the mushrooms in the dark are active[3](https://www.lib.uchicago.edu/about/news/foxfire-and-fungi-solving-a-2300-year-old-mystery/). Researchers also propose that bioluminescence may primarily function as a defense against oxidative stress, and that in some species, life cycle phases, or environmental conditions the glow may be merely an accidental metabolic byproduct[1](https://pmc.ncbi.nlm.nih.gov/articles/PMC11766655/).
## Folklore and history
The name foxfire has nothing to do with foxes, but the same metaphor arose independently in Japan: old Japanese called an unknown ground glow Kitsune-bi, meaning "fox's fire", and both Kitsune-bi and Mino-bi ("raincoat fire", a glow attributed to wet straw raincoats) are partly considered responsible for luminous mycelia growing on rotten wood or straw[7](https://pmc.ncbi.nlm.nih.gov/articles/PMC10302135/). In 1555 the Swede Olaus Magnus published a history mentioning numerous luminescent mushrooms and their connection to wood decay, and described the practical use of mycelia-infested bark, often called "Foxfire" or "Faerie fire", by Scandinavians during long winter nights; in the 1600s a Dutch physician noted Indonesian cultures using luminescent fungi as improvised torches[2](https://blog.mycology.cornell.edu/2010/04/12/this-bark-glows-in-the-dark-bioluminescence-in-mushrooms/) • [3](https://www.lib.uchicago.edu/about/news/foxfire-and-fungi-solving-a-2300-year-old-mystery/). As recently as the 20th century, Micronesian cultures incorporated luminescent fungi into ritual dress and face paint[3](https://www.lib.uchicago.edu/about/news/foxfire-and-fungi-solving-a-2300-year-old-mystery/).
## References
1. [Diversity, Distribution, and Evolution of Bioluminescent Fungi, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC11766655/)
2. [This bark glows in the dark! Bioluminescence in mushrooms, Cornell Mushroom Blog](https://blog.mycology.cornell.edu/2010/04/12/this-bark-glows-in-the-dark-bioluminescence-in-mushrooms/)
3. [Foxfire and fungi: Solving a 2,300 year-old mystery, The University of Chicago Library News](https://www.lib.uchicago.edu/about/news/foxfire-and-fungi-solving-a-2300-year-old-mystery/)
4. [Current Status of Research on Fungal Bioluminescence: Biochemistry and Prospects for Ecotoxicological Application, Photochemistry and Photobiology](https://doi.org/10.1111%2Fphp.12135)
5. [Fungal Bioluminescence: Past, Present, and Future, Diversity](https://www.mdpi.com/1424-2818/16/9/539)
6. [Bioluminescence – The Vibrant Glow of Nature and its Chemical Mechanisms, ChemBioChem](https://chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/cbic.202400106)
7. [The Luminous Fungi of Japan, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC10302135/)
8. [Mechanism and color modulation of fungal bioluminescence, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC5406138/)
9. [Understanding and using fungal bioluminescence – Recent progress and future perspectives, Current Opinion in Green and Sustainable Chemistry](https://www.sciencedirect.com/science/article/pii/S2452223621001267)
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*Topic: Encyclopedia › Life and health › Microorganisms and fungi › Fungi and mycology › Basidiomycete taxa › Basidiomycetes overview*
*Initially written Sep 17, 2026 · Reviewed: Sep 30, 2026; Oct 21, 2026 · Edited: Oct 15, 2026; Oct 21, 2026 · Last review: Oct 21, 2026*
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License: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license