After a week of soggy weather, the fairies have been dancing on lawns all across north Texas:
Notice how the toadstools are making a nice little circle all around this Crape Myrtle?
These toadstools are called Green-Spored Lepiota (Chlorophyllum molybdites). They're the number one most common cause of wild mushroom poisoning in the United States.
A fairy ring, traditionally, was the circular pattern of toadstools left behind after the fairies and pixies danced on your lawn in the middle of the night. If you sit inside the fairy ring at night and sleep there, the fairies are compelled to leave and never return.
This particular kind of fairy ring doesn't harm your lawn, but you'll want to be sure to keep little children and pets from ingesting any of these poisonous fellows. Other types of fairy rings *do* harm your lawn, though there isn't a great deal you can do to control them other than removing the dirt they're growing in, because they're coming from an underground mycelium. The mushrooms you see are just the fruiting body of a much larger underground organism.
Regardless of all the science and folklore, I love seeing the fairy rings popping up all over. Either way you look at it (scientific or magical), it's evidence of the unseen.