Puffballs are round or pear-shaped fruiting bodies that sit directly on the ground or on rotted wood. They come in several different shapes; their relatives include the Earth star and the giant puffball. In the eastern and central United States and Canada, they are frequently found sitting on the ground in the summer and fall—most looking like a medium-brown ping-pong ball (although some can reach the size of a small watermelon). If you squeeze the puffball, the thin skin will crack open and the insides will fall out like a puff of smoke. In reality, the “smoke” particles are spores—each about 3.5 to 5.5 micrometers (MGRm; 0.00014–0.00019 inch) in diameter. Thousands of spores are in one puffball; in fact, a giant puffball (Calvatia gigantean) can contain more than seven trillion spores!