There have been many explanations for these enchanting circles over the centuries, from fairies to witches, dragons to the Devil and snail trails to lightning, but now science is starting to reveal more of the workings of their mysterious world.
The supernaturalist Sir Arthur Conan Doyle, who in later life became known as a “great protagonist for the existence of fairies", noted that mushroom rings have “from all time...been associated with the gambols of the little people" (Rolfe and Rolfe 1925). Folklore has made many attempts to explain their enchanting growth pattern. While in Britain these mysterious circles are known universally as “fairy rings”, their relationship with the supernatural changes with geography. The Germans call them “Hexenringe”, literally "witches' rings" and meaning “the circles that witches form while dancing", while in the Tyrol, Austria, the dead ring of grass they create is attributed to the actions of dragons. In France, meanwhile, they are called “Ronds de Sorcières” (also witches' rings) and within them, “enormous toads with bulging eyes are said to appear" (Findlay, 1982). In Switzerland and Russia, they concealed hidden treasure, which fairies or witches could help reveal (Findlay 1982).
Fairy rings haven’t just attracted myth but also everyday superstitions. In Britain, and especially Wales, people were wary of stepping inside the rings, as it was rumoured the fairies would cause you to dance yourself to exhaustion or death. In The Tempest, Shakespeare recounted the folk belief that sheep were reluctant to graze within the circles of dead and lush grass fungus creates. Prospero addresses the Elves of the Hills:
You demi-puppets that by moonshine do the green-sour ringlets make,
Whereof the ewe not bites, and you whose pastime is to make midnight mushrooms.
There are around 60 species of fungi able to form rings that can be divided into two types: “free” fairy ring fungi, which are saprobic and feed on dead or living organic matter such as thatch or leaf litter, and “tethered” species, which are mycorrhizal and form symbiotic relationships with trees. While free species form circles of fruiting bodies, at other times they are marked only by the lush green and dead rings they leave on the turf or no trace at all. Woodland species, meanwhile, leave no obvious marks, only appearing as circles of mushrooms.
In the sixteenth century, scientists posited that it was lightning that caused the circular scars on grassland, while Bradley in 1789 thought it was ants, flinging up fine soil and improving grass growth in the vicinity. He also pointed the finger at slugs and snails, whose mucus trails, laid in courtship, encouraged “toadstools” to spring from the soil. It wasn’t until William Withering, in 1792, that fungi were identified as the cause (Dugan, 2008).
Subsequently, we have been offered more accurate insight into how these rings are formed and the relationship they have with the surrounding landscape. We now know they are created as the fungi’s mycelium grows radially, using up the nutrients in the soil and creating a ring of dead grass. The circle of lush grass is created by the nitrogen released as the fungus digests organic matter — although these mechanisms vary from species to species. As the mycelial front advances the mycelium as the centre of the ring decays.
Of the meadow species, the most ubiquitous is the fairy ring champignon or mousseron (Marasmius oreades). Mousserons, which appear in late spring through to early Autumn, are a fascinating species for several reasons. They are known as the “resurrection mushroom” because of a curious adaptation to hot weather: they are able to dry out completely but re-
inflate when soaked by rain. Not only do they regain their shape and colour but they are also able to create new spores and cells. They are able to do this through a high concentration of the sugar trehalose, which protects against cell damage.
While this unusual ability has attracted the attention of researchers, they have also been drawn to study the genetics of the rings they create. Fairy rings are long-lived and their age can be estimated by measuring their diameter. Mycellium is thought to advance from the centre of the ring by six to 18 inches each year and the oldest examples, such as a giant ring of trooping funnel (Infundibulicybe geotropa) in Belfort, France, are thought to be in excess of 700 years old.
Markus Hitunen (2021), who has studied Marasmius oreades, believes that their longevity means the rings can be thought of as “natural, long-term evolutionary experiments". Each ring, with a common origin, expands outwards, so he believed each sector would accumulate independent genetic mutations. The fungus was found to be extremely stable, however, and the few mutations that did arise were not transmitted to the spores, suggesting it possesses a yet-unidentified mechanism for mutation suppression.
Grassland management, both for ecological purposes and the maintenance of manicured areas like lawns and golf courses, has also shone the spotlight on the behaviour of mousseron rings — and they have been found to bring both life and death to ecosystems. Three mechanisms have been observed to create the necrotic areas of grass. Firstly, the fungus has been shown to directly parasitise the roots of grass species, including Poa pratensis, Festuca rubra, and Agrostis tenuis (Filer, 1965). The mycelium also turns the soil water repellant inside the ring — not a problem for a species that can survive desiccation but destructive to its neighbours (York and Canaway, 2000). Thirdly, the fungus produces cyanide and concentrations were found to be high enough within 25cm of a ring to inhibit grass root growth and also greatly inhibit the growth of some other fungal species (Blenis et al., 2004).
As you may expect from this chemistry, neighbouring plant species have been shown to change dramatically in response to fairy ring development. A study of field mushroom (Agaricus campestris) rings showed soil which the mycelia has passed through was not only significantly more hydrophobic but also had mineral and electrical changes. By killing grasses and impacting soil composition, fairy rings both damage and enhance as they go. The bright side is that this creates empty niches for rare, short-lived species (Bonanomi et al., 2012, Bonanomi et al., 2013). Fairy rings can also have other ecological impacts: mousseron have been shown to have a talent for mycoremediation of heavy metals, particularly titanium and bismuth (Elekes & Busuioc, 2010).
Unlike the genetically concordant rings of mousseron, ectomycorrhizal fungi growing in rings in woodland settings have been shown to form more like families, suggesting sexual reproduction plays a more important role in their creation. Tricholoma matsutake, a highly desirable edible in Japan, hosted by pine trees, forms dense mats of mycelium or “shiros” beneath the litter layer, which consist of multiple genotypes (Peter, 2006). Lian et al (2006) used microsatellite markers to explore the relationship between fungi and host and showed each genetically-individual group was associated with more than one tree. This provides additional evidence for the existence of a “wood wide web” through which plants, fungi and hosts have been shown to transfer carbon (Simard & Durrall, 2004). As you might expect from a symbiotic fungus, these woodland species are less damaging than their meadow counterparts: soil within the centre of mycorrhizal fungi rings has been shown to return to its former state once the mycelia have past through (Peter, 2006).
It's inevitable that long-lived species will attract attention and, including the ancient ring of trooping funnel in France, there are sites at which fairy rings have become a known spectacle. Meadow species such as mousseron are particularly fond of calceaeous land and are known to colonise swathes of the south downs. The chalk-based Salisbury Plain is also home to some historic rings. One, near Stonehenge, is alleged to be 1,000 years old (Millman, 2019). Fairy rings are certainly a feature of this neolithic monument. Aerial pictures from the 1906 show many of them marking the landscape, while Jean Grey, daughter of 1930s Stonehenge custodian John Moffat, has childhood memories of picking mushrooms from the rings (English Heritage, n.d).
It’s here that the fairies and the fungi reconvene. In Ireland, there is an old association between fairies, fungi and megaliths, as it was sometimes believed that the stone circles were relics erected overnight and "credited to the industry of the fairies... giants or the Devil" (Gill 1944). Gill also notes that the same Gaelic expression for "a one night's growth" (fás na h-aon oidhche) was applied both to the megalithic structures and to mushrooms (Dugan, 2008). It certainly begs the question of just where the ancients got the idea.
Bonanomi, G., Mingo, A., Incerti, G., Mazzoleni, S., & Allegrezza, M. (2012). Fairy rings caused by a killer fungus foster plant diversity in species-rich grassland. Journal of Vegetation Science, 23(2), 236–248.
Bonanomi, G., Incerti, G., & Allegrezza, M. (2013). Assessing the impact of land abandonment, nitrogen enrichment and fairy-ring fungi on plant diversity of Mediterranean grasslands. Biodiversity and Conservation, 22, 2285-2304.
Blenis, P. V., Chow, P. S., Duncan, I., & Knowles, N. R. (2004). Cyanide levels near fairy rings affect the growth of grasses and fungi. Canadian Journal of Botany, 82(9), 1324–1329.
Dugan, F. (2008). Fungi, Folkways and Fairy Tales: Mushrooms & Mildews in Stories, Remedies & Rituals, from Oberon to the Internet. North American Fungi, 3(7), 23–72.
English Heritage (n.d) Stonehenge exhibition reveals unique memories of 1930s childhood at the stones. Retrieved June 30, 2022, from English Heritage website: https://www.english-heritage.org.uk/about-us/search-news/pr-stonehenge-1930s-memories/
Elekes, C. C., & Busuioc, G. (2010). The mycoremediation of metals polluted soils using wild growing species of mushrooms. Latest Trends in Engineering Education, 36–39.
Filer, T. H. (1965). Parasitic aspects of a fairy ring fungus, Marasmius oreades. Phytopathology 55(10):1132-1134.
Findlay, W. P. K. (1982). Fungi Folklore, fiction, and fact. Richmond: The Richmond Publishing Co. Ltd.
Gill, W. W. (1944). The one-night house. Folklore 55: 128-132.
Hiltunen, M., Ament-Velásquez, S. L., & Johannesson, H. (2021). The Assembled and Annotated Genome of the Fairy-Ring Fungus Marasmius oreades. Genome biology and evolution, 13(7), evab126.
Hiltunen, M., Grudzinska-Sterno, M., Wallerman, O., Ryberg, M., & Johannesson, H. (2019). Maintenance of High Genome Integrity over Vegetative Growth in the Fairy-Ring Mushroom Marasmius oreades. Current Biology, 29(16), 2758-2765.e6.
Lian, C., Hogetsu, T., Lian, C., Narimatsu, M., Nara, K. &Hogetsu T. (2006) Tricholoma matsutake in a natural Pinus densiflora forest: correspondence between above- and below-ground genets, association with multiple host trees and alteration of existing ectomycorrhizal communities. New Phytol. 171:825–883.
Millman, L. (2019). Fungipedia: A Brief Compendium of Mushroom Lore. Princeton University Press.
Peter, M. (2006). Ectomycorrhizal fungi – fairy rings and the wood-wide web. New Phytologist, 171(4), 685–687.
Rolfe, R. T., & Rolfe, F. W. (1928). The romance of the fungus world; an account of fungus life in its numerous guises, both real and legendary, by R.T. Rolfe and F.W. Rolfe; with foreword by J. Ramsbottom. Philadelphia, J.B. Lippincott Co.
Sikes, W. (1880). British Goblins: Welsh Folk-lore, Fairy Mythology, Legends and Traditions pp. 74. London: Sampson Low, Marston, Searle, & Rivington.
York, C. A., & Canaway, P. M. (2000). Water repellent soils as they occur on UK golf greens. Journal of Hydrology, 231-232, 126–133.