Fairy ring

Fairy Rings are naturally occurring rings of mushrooms that are said to be locations where Fairies congregate.

Mythology and Folklore
There are numerous myths concerning fairy rings found all throughout Europe.

English and Celtic Mythology
According to English and Celtic mythology fairy rings are cause by fairies and elves dancing around in a circle at night. If any human who stumbles upon these festivities enters the fairy ring, they are forced to dance until they go insane, die or pass out from exhaustion.

German Mythology
According to German mythology fairy rings are called "witches rings." It's believed that on Walpurgisnacht, the spring celebration six months before Halloween, witches gather to dance in circles, leaving the rings of mushrooms.

Dutch Mythology
According to Dutch mythology fairy rings are locations in which the devil would churn his milk. It is said that any cows that enter one of these fairy rings would have their milk turn sour.

Austrian Mythology
According to Austrian mythology, fairy rings are the result of dragons burning circular rings into the forest floor with their fiery tails.

Biological Explanation
Fairy rings are can be formed by a variety of species of mushroom, but are most commonly found with Agaricus campestris, a type of field mushroom. The rings of mushrooms formed are typically around two meters (six feet) in diameter, but can be larger.

Fairy rings are formed when a mushroom spawn falls in a favorable spot to grow. The spawn, known as a mycelium, begins to send out small subterranean fibers, called hyphae, in all directions forming a circular mat below the surface of the soil. As the mycelium grows outward, the center of the circular mat begins to die off, so that any mushrooms that develop above the surface appear in a ring-like pattern. As this process continues, the ring becomes wider and wider until sections of the ring begin to die off, leaving only unconnected patches of mushrooms.