Over a hundred fungal species glow in the dark

Fungal bioluminescence is not reflected light, nor the effect of phosphorus deposited on a cap. It is a chemical reaction taking place in living cells. Fungal luciferin, 3-hydroxyhispidin, is oxidised by the enzyme luciferase, and part of the energy released appears as greenish light. The same mechanism has been found in glowing species from different lineages of the Agaricales, which has helped in understanding the evolution of the trait.

The list of known glowing fungi has passed a hundred species, but they do not all glow in the same way. In some the gills or the whole fruiting body are visible; in others it is mainly the mycelium in wood. Intensity depends on temperature, humidity, the age of the tissue and the time of day. The glow may be so faint that it appears only after ten or fifteen minutes of dark adaptation, or in a photograph taken with a long exposure. Striking photographs therefore do not show how bright a fungus looked to an observer in the forest.

What is the light for? There is no single answer for all species. In experiments, glowing decoys attracted more insects than dark ones, which supports the hypothesis of spore dispersal by nocturnal invertebrates. In species whose fruiting bodies do not glow while the hidden mycelium does, that explanation is less convincing. Luminescence may also be a by-product of metabolism, or serve several functions depending on the environment.

In Poland the phenomenon known as foxfire is most easily met in rotting wood colonised by honey fungus. Do not expect a neon cap: more often, once a torch is switched off, a very faint glow from exposed mycelium becomes visible. There is no need to take the wood. It is enough to shield the eyes from light, wait, and remember that identifying any species requires characters other than the glow itself. Bioluminescence should also not be confused with fluorescence. A fluorescent material needs external light, such as ultraviolet, whereas a living bioluminescent fungus drives the emission itself by a metabolic reaction.

What the evidence actually shows

Fungal bioluminescence is not phosphorescence: the light is continually produced by an oxygen-dependent chemical reaction. Kotlobay and colleagues reconstructed a pathway in which hispidin is converted into fungal luciferin and luciferase oxidizes it, emitting green light near 520–530 nm. The pathway genes occur together in a cluster, helping explain the shared evolutionary origin of light production within several agaric lineages. A recent review catalogues 132 luminous taxa, but that total is not immutable; it changes as species are described and old reports are verified. Depending on the species, the cap, gills, stem, or only the mycelium may glow. Ecological function is not universal either. Experiments in some species indicate that light can attract invertebrates capable of moving spores, but this should not be presented as the established purpose of luminescence in every glowing fungus.

How do you test whether light attracts insects?

A photograph of an insect on a glowing mushroom does not establish what attracted it. Smell, moisture or shelter could also explain the visit. A study published in 2015 therefore used acrylic mushroom models, some illuminated by green LEDs and others kept dark. The illuminated models trapped more insects. This design tested light separately from the other properties of a living fruiting body. The researchers also described a daily luminescence rhythm in Neonothopanus gardneri. The 2015 study supports attraction of potential spore carriers, although arrival at a trap is not itself a measurement of successful establishment at a new site.

An Australian study of Omphalotus nidiformis provides a useful comparison. Traps baited with glowing fruiting bodies did not catch significantly more insects than controls. The fruiting bodies also glowed during daylight and appeared in winter, when insect activity was low. The 2016 result shows why two luminous species may need different ecological explanations. Failure to detect an effect in this experiment does not establish that light can never have any function. It narrows a particular hypothesis under particular conditions.

From a forest phenomenon to a research tool

Once understood, the light-producing pathway can become a biological reporter: in an appropriately engineered system, light provides a readout of the process being studied. In work published in 2024, modified enzymes increased the signal in tested plant, fungal and mammalian cells relative to the original pathway. This is an engineering result for a defined system, not evidence that wild mushrooms have suddenly become brighter. The Nature Methods paper demonstrates applications in imaging.

When reading such a report, separate three questions: how light is produced, what it does for a fungus in nature, and how people can use the mechanism. Answering one does not settle the others. The same distinction helps when viewing a striking photograph. An image can document light emission without establishing its ecological purpose. The experiment, its control and the measured outcome tell us which part of the story has actually been tested.