Naturally occurring ring or arc of mushrooms
A fairy ring, also known as fairy circle, elf circle, elf ring or pixie ring, is a naturally occurring ring or arc of mushrooms. They are found mainly in forested areas, but also appear in grasslands or rangelands. Fairy rings are detectable by sporocarps (fungal spore pods) in rings or arcs, as well as by a necrotic zone (dead grass), or a ring of dark green grass. Fungus mycelium is present in the ring or arc underneath. The rings may grow to over in diameter, and they become stable over time as the fungus grows and seeks food underground.
Fairy rings are the subject of much folklore and myth worldwide, particularly in Western Europe. They are alternately seen as hazardous or dangerous places linked with witches or the Devil, or as a sign of good fortune.
Genesis.
The mycelium of a fungus growing in the ground absorbs nutrients by secretion of enzymes from the tips of the hyphae (thread-like branching filaments making up the mycelium). This breaks down larger molecules in the soil into smaller molecules that are absorbed through the hyphae walls near their growing tips. The mycelium moves outward from the center, and when the nutrients in the center are exhausted, the center dies, forming a living ring, from which the fairy ring arises.
There are two theories regarding the process involved in creating fairy rings. One states that the fairy ring is begun by a spore from the sporocarpus. The underground presence of the fungus can also cause withering or varying colour or growth of the grass above. The second theory, which is presented in the investigations of Japanese scientists on the "Tricholoma matsutake" species, shows that fairy rings could be established by connecting neighbouring oval genets of these mushrooms. If they make an arc or a ring, they continuously grow about the centre of this object.
Necrotic or rapid growth zones.
One of the manifestations of fairy ring growth is a necrotic zone—an area in which grass or other plant life has withered or died. During a dry year, these zones are caused by the mycelia, which coat the roots of grasses and other herbs in meadows. After some time, they are removed by biotic factors from the ground; at this stage, a zone on the surface soil becomes visible. Patterns other than the basic ring or arc are also possible: circles, doubled arcs, sickle-shaped arcs, and other complicated formations are also formed by this process. Fungi can deplete the soil of readily available nutrients such as nitrogen, causing plants growing within the circle to be stressed, which leads to plant discoloration. Some fungi also produce chemicals that act like hormones called gibberellins, which affect plant growth, causing rapid luxuriant growth.
Long-term observations of fairy rings on Shillingstone Hill in Dorset, England, further suggested that the cycle depended on the continuous presence of rabbits. Chalky soils on higher elevations in the counties of Wiltshire and Dorset in southern England used to support many meadow-type fairy rings. Rabbits crop grass short in open areas and produce nitrogen-rich droppings. Mushrooms need more soil nitrogen than grass does. A ring can start from only a few spores from which the mycelium develops; the fruiting bodies of the mushrooms appearing only later when sufficient mycelial mass has been generated to support them. Subsequent generations of fungi grow only outward because the parent generations have depleted their local nitrogen levels. Meanwhile, rabbits keep cropping the grass, but do not eat the fungi, allowing them to grow through their competition to tower, relatively, above the grass. By the time a circle of mushrooms reaches about in diameter, rabbit droppings have replenished the nitrogen levels near the centre of the circle, and a secondary ring may start to grow inside the first.
Soil analysis of soil containing mycelium from a wood blewit ("Clitocybe nuda") fairy ring under Norway spruce ("Picea abies") and Scots pine ("Pinus sylvestris") in southeast Sweden yielded fourteen halogenated low molecular weight organic compounds, three of which were brominated and the others chlorinated. It is unclear whether these were metabolites or pollutants. Brominated compounds are unknown as metabolites from terrestrial fungi.
Types.
There are two generally recognised types of fairy ring fungus. Those found in the woods are called "tethered" because they are formed by mycorrhizal fungi living in symbiosis with trees. Meadow fairy rings are called "free" because they are disconnected from other organisms. These mushrooms are saprotrophic. The effects on the grass depend on the type of fungus that is growing; when "Calvatia cyathiformis" is growing in the area, grass grows more abundantly; however, "Leucopaxillus giganteus" causes the grass to wither.
Species involved.
About 60 mushroom species can grow in the fairy ring pattern. The best known is the edible Scotch bonnet ("Marasmius oreades"), commonly known as the fairy ring champignon.
One of the largest rings ever found is near Belfort in northeastern France. Formed by "Infundibulicybe geotropa", it is thought to be about in diameter and over 700 years old. On the South Downs in southern England, "Calocybe gambosa" has formed huge fairy rings that also appear to be several hundred years old.
Cultural references.
Oral tradition and folklore.
A great deal of folklore surrounds fairy rings. Their names in European languages often allude to supernatural origins; they are known as ("witches' circles") in French, and ("witches' rings") in German. In German tradition, fairy rings were thought to mark the site of witches' dancing on Walpurgis Night, and Dutch superstition claimed that the circles show where the Devil set his milk churn. In Tyrol, folklore attributed fairy rings to the fiery tails of flying dragons; once a dragon had created such a circle, nothing but toadstools could grow there for seven years. European superstitions routinely warned against entering a fairy ring. French tradition reported that fairy rings were guarded by giant bug-eyed toads that cursed those who violated the circles. In other parts of Europe, entering a fairy ring would result in losing an eye. Fairy rings are associated with diminutive spirits in the Philippines.
Western European traditions, including English, Scandinavian, and Celtic, claimed that fairy rings are the result of elves or fairies dancing. Such ideas dated to at least the mediæval period; The Middle English term "" ("elf-ring"), meaning "a ring of daisies caused by elves' dancing" dates to the 12th century. In his "History of the Goths" (1628), Swedish writer Olaus Magnus makes this connection, saying that fairy rings are burned into the ground by the dancing of elves. British folklorist Thomas Keightley noted that in Scandinavia in the early 19th century, beliefs persisted that fairy rings ("elfdans") arose from the dancing of elves. Keightley warned that while entering an "elfdans" might allow the interloper to see the elves—although this was not guaranteed—it would also put the intruder in thrall to their illusions.
The folklores of Britain and Ireland contain a wealth of fairy lore, including the idea from which fairy rings take their name: the phenomena result from the dancing of fairies. In 19th-century Wales, where the rings are known as "", fairies were almost invariably described as dancing in a group when encountered, and in Scotland and Wales in the late 20th century, stories about fairy rings were still common; some Welshmen even claimed to have joined a fairy dance. Victorian folklorists regarded fairies and witches as related, based in part on the idea that both were believed to dance in circles. These revels are particularly associated with moonlit nights, the rings becoming visible to mortals only the following morning. Local variants add other details. An early 20th-century Irish tradition says that fairies enjoy dancing around the hawthorn tree so that fairy rings often centre on one. One resident of Balquhidder, Scotland, said that the fairies sit on the mushrooms and use them as dinnertables, and a Welsh woman claimed that fairies used the mushrooms as parasols and umbrellas. Olaus Magnus in "Historia de Gentibus Septentrionalibus" wrote that the brightness of the fairy ring comes not from the dancing of the fairies, who harm it with their feet, but from Puck, who refreshes the grass. A Devon legend says that a black hen and chickens sometimes appear at dusk in a large fairy ring on the edge of Dartmoor. A Welsh and Manx variant current in the 1960s removes dancing from the picture and claims that fairy rings spring up over an underground fairy village. These associations have become linked to specific sites. For example, "The Pixies' Church" was a rock formation in Dartmoor surrounded by a fairy ring, and a stone circle tops Cader Idris in northern Wales, believed to be a popular spot for fairy dances.
Many folk beliefs generally paint fairy rings as dangerous places, best avoided. American writer Wirt Sikes traces these stories of people trespassing into forbidden territory and being punished for it to the tale of Psyche and Eros. In it, Psyche is forbidden to view her lover; when she does so, her palace disappears, and she is left alone. Superstition calls fairy circles sacred and warns against violating them lest the interloper (such as a farmer with a plough) anger the fairies and be cursed. In an Irish legend recorded by Wilde, a farmer builds a barn on a fairy ring despite the protests of his neighbours. He is struck senseless one night, and a local "fairy doctor" breaks the curse. The farmer says that he dreamed that he must destroy the barn. Even collecting dew from the grass or flowers of a fairy ring can bring bad luck. Destroying a fairy ring is unlucky and fruitless; superstition says it would simply grow back.
A traditional Scottish rhyme sums up the danger of such places:
 ;templatestyles src="Template:Blockquote/styles.css" / ;
Numerous legends focus on mortals entering a fairy ring—and the consequences. One superstition is that anyone who steps into an empty fairy ring will die at a young age. A 20th-century tradition from Somerset calls the fairy ring a "galley-trap" and says that a murderer or thief who walks in the ring will be hanged. Most often, someone who violates a fairy perimeter becomes invisible to mortals outside and may find it impossible to leave the circle. Often, the fairies force the mortal to dance to the point of exhaustion, death, or madness. In Welsh tales, fairies actively try to lure mortals into their circles to dance with them. A tale from the Cambrian Mountains of Wales, current in the 19th century, describes a mortal's encounter with a fairy ring:
 ;templatestyles src="Template:Blockquote/styles.css" / ;... he saw the Tylwyth Teg, in appearance like tiny soldiers, dancing in a ring. He set out for the scene of revelry, and soon drew near the ring where, in a gay company of males and females, they were footing it to the music of the harp. Never had he seen such handsome people, nor any so enchantingly cheerful. They beckoned him with laughing faces to join them as they leaned backward almost falling, whirling round and round with joined hands. Those who were dancing never swerved from the perfect circle; but some were clambering over the old cromlech, and others chasing each other with surprising swiftness and the greatest glee. Still others rode about on small white horses of the most beautiful form ... All this was in silence, for the shepherd could not hear the harps, though he saw them. But now he drew nearer to the circle, and finally ventured to put his foot in the magic ring. The instant he did this, his ears were charmed with strains of the most melodious music he had ever heard.
Entering the ring on May Eve or Halloween night was especially dangerous. One source near Afon fach Blaen y Cae, a tributary of the Dwyfach, tells of a shepherd accidentally disturbing a ring of rushes where fairies are preparing to dance; they capture him and hold him captive, and he even marries one of them. In variants from Scotland recorded by Edwin Sidney Hartland in 1891, the ring is replaced by a cavern or an old mill.
Freedom from a fairy ring often requires outside intervention. A tactic from early 20th-century Wales is to cast wild marjoram and thyme into the circle and befuddle the fairies; another asks the rescuer to touch the victim with iron. Other stories require that the enchanted victim simply be plucked out by