These are a type of fungus called Earth Stars, and they have a very special way of reproducing. Instead of forming seeds, fungi form spores, which are very tiny. As the Earth Star forms, it looks somewhat like a Puffball. Its scientific name (Astraeus hygrometricus) gives a clue. The humidity just before it rains causes the outer layer of the Earth Star splits into sections which open outwards, causing it to act as a hygrometer, detecting high humidity. The sections form the star shape that gives them their name Earth Star. The inner part has a hole in the top. As raindrops fall, they hit the Earth Star, causing puffs of spores to be forced out of the tiny hole in the top. These spores are spread by air and by water, letting the Earth Stars spread to new areas.