This is a collection of notes about Foxfire. It's intended that this will eventually become a more properly groomed article, but meanwhile it is hoped that the content will be of some use to someone.
foxfire - n. 1. The phosphorescent light emitted by decaying timber. Usage: 1483 Cath. Angl. [Catholicon Anglicum] 140 Fox Fire, glos, glossis. 1824 J. DODDRIDGE Notes Virginia & Pennsylv. 290 If they had seen any thing like fire, between that and the fort, it must have been fox fire.
—The Oxford English Dictionary, 2nd Ed.
Foxfire is a natural phenomenon sometimes visible at night in forests. It's caused by bioluminescent fungi in special conditions—usually on rotting bark. Foxfire is caused by a range of different species of fungi, though Armillaria mellea appears to be the most common source. This particular species emits a bluish-green glow, like glow in the dark toys. I've also come across reports of redish lights, however, which are most probably caused by other species.
List of species which may cause bioluminescence: Armillaria mellea, Armillaria ostoyae, Collybia tuberosa (luminescent sclerotia*), Mycena chlorophos (Mycena chlorophanos), Mycena citricolor (Omphalia flavida), Mycena rorida (luminous spores), Omphalotus olearius (Clitocybe illudens, Omphalotus illudens, Jack-o'-lantern), Panellus stipticus (North American, not Eurasian, only), and Pleurotus nidfformis (Ghost Fungus). Source, e.g. sari.ac.uk; note also that Bioluminescence in Fungi says that the "bioluminescent ability occurs in 25 different phyla many of which are totally unrelated". There are some illustrations of Mycena chlorophos glowing at the Springbrook Research Centre, and Luxgene (at bioart.co.uk) has several illustrations of species that cause foxfire:
"A substance called luciferin reacts with an enzyme, luciferase, causing the luciferin to oxidise, with the consequent emission of light. [...] The function in fungi is unknown. It has been suggested that it attracts insects which then disperse the spores."—Luminous Fungi.
Recorded observations of fungal luminescence date back to Aristotle and Pliny the Elder. Pliny identified an "Agaricke" that "grows on the tops of trees and shines at night." Renaissance philosophers wrote of `"Fungus igneus, which shines like stars with a bluish light." In folklore, "Fairy sparks" in decaying wood indicated the place where fairies held their nightly revels.
—BIOLUMINESCENCE FUNGI: LIVING LIGHT, Spores Illustrated, Conn.-Westchester Myco. Assoc., Summer 1999, via Boston Mycological Club Bulletin, Sept. 1999
"The results suggested that bioluminescence is linked to metabolic activity in A. mellea, M. citricolor, O. olearius, but not in P. stipticus." - Naturally bioluminescent fungi - a new perspective, Hedda J Weitz, University of Aberdeen.
Foxfire depends upon a number of conditions to survive, but once taken from the wild it's been known to be quite durable, lasting for days in people's fridges, or being posted through the mail, etc. It's even been put to practical purposes in the past:
People from many parts of the world have found uses for these natural lanterns. The Swedish historian Olaus Magnus wrote in 1652 that people in the far north of Scandinavia would place pieces of rotten oak bark at intervals when venturing into the forest. They could then find their way back by following the light.
—Elio Schaechter, from his book In the Company of Mushrooms
In an episode of Lassie, Timmy and Boomer hunt for foxfire so as to scare the girls into not kissing them at the Hallowe'en party.