Despite its wonderfully mysterious name, “foxfire” is not a fire, nor is it at all related to foxes. It is, in fact, caused by the lowly mushroom.

Also known as “will-o’-the’wisp,” “torchwood,” or “faerie fire,” foxfire is actually a greenish glow that is caused by bioluminescent fungi that are located under leaves, inside rotting wood, and in other undisturbed damp places in wooded areas.

Bioluminescent plants are plants which contain chemicals that cause the plant to glow under very dark conditions. This is similar to fireflies in the way they produce their light. An enzyme called luciferase (from “lucifer”, meaning “light-bearer” in Greek) reacts with the oxygen in the air and creates the greenish-white light that is so often seen in forests, especially ones with a lot of oak trees.

Elio Schaechter, a noted mycologist, states in his book that “The greenish light, known as “foxfire,” is given out not only by the mushrooms themselves but also by the mycelium, the fungal filaments that often permeate the wood of diseased trees. The surface layers of the mycelium of such impregnated wood, which is called ‘touchwood,’ can be seen to glow fairly brightly for one or two weeks.”

Although many fungi around the world are bioluminescent, there are several kinds of fungi in particular that are responsible for this light. Armillaria, or honey mushrooms, makes up the majority of foxfire found in North America. Jack o’Lantern mushrooms, and their California cousin, the Western Jack o’Lantern mushroom, also play a role as does Pleurotus nidfformis, the eerily named Ghost Fungus.

Foxfire in History

Foxfire has been noticed and used since ancient times. In 382 B.C., Aristotle wrote about this phenomena, calling it as “luminous wood.” Pliny, a Roman naturalist, describes olive groves with the same luminous wood. In the Renaissance, scientists wrote about “Fungus igneus, which shines like stars with a bluish light.” Other descriptions have been found in Roman and Indian lore.

During the Revolutionary war, the inventor of the first battle submarine used foxfire. David Bushnell realized that he would need a method of lighting the inside of the ship. At first he planned to use candles, but after thinking about this he realized that the candle would use up a great deal of the small amount of oxygen that would be available inside the submarine. He turned to Benjamin Franklin for advice.

Franklin, noted for his scientific acumen and his ability to think outside the box, thought of using foxfire to give the pilot enough light for at least the depth meter and the compass. The illumination provided was apparently sufficient at night, although it was dimmer than expected because the cooler temperatures once the submarine was in the ocean caused the fungi’s metabolism to slow down which reduced the glow.

Mark Twain used the idea of foxfire as a source of light in his book, Huck Finn. Huck says that he and Tom needed light so they went into the woods and got “a lot of them rotten chunks that’s called fox-fire, and just makes a soft kind of a glow when you lay them in a dark place.”

In World War II, troops stationed in the Pacific found uses for this fungi, often putting them on their helmets and weapons so they could spot each other in the dark without attracting the notice of the enemy. The British mycologist John Ramsbottom reported that American war correspondent George Wallerk, on assignment in New Guinea, began a letter to his wife, “Darling, I am writing to you tonight by the light of five mushrooms.”

Foxfire Today

As the amount of forested area dwindles, few people are familiar with foxfire. They simply do not see it as often. It is still there, however. In an interview with Chicago Wilderness Magazine, Gregg Mueller, a mycologist at Chicago’s Filed Museum, says, “The honey mushroom is bright enough to see in the woods on a moonless or cloudy night in autumn. That’s when people call and tell me that their wood piles are glowing.”

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