English folklore, fairy rings were said to be caused by elves, fairies or pixies dancing in a circle, wearing down the grass beneath their feet. Toads would then sit on the mushrooms, poisoning them; hence the name toadstool. In Sussex they were called, “hag tracks”, in Devon people thought that fairies caught young horses and rode them in circles.
Another myth states that fairy rings are doors into the fairies' world, transporting people to other places or making people appear in the same place in a different time. Young ladies are also warned not to touch the dew on the grass within the ring, as it is believed that it can cause skin problems.
One of the largest rings ever found is in France. It is thought to be about 800 m in diameter and over 700 years old.
an old medieval belief that the rings represented places where witches would have their gatherings. In Austria people thought that dragons' breath burned the land.
Interesting, views on a natural phenomena.