A Ginormous Mushroom

It's not uncommon for us to find wild mushrooms growing in our yard during the summer, particularly when we've had some humid weather (and no, we NEVER eat them--not worth the risk!), but every once in a while we get a giant mushroom like this one: 

I'm told it's a "puffball mushroom". This one seems to love the spotlight--literally! It's already almost the size of a volleyball, and still growing.  I'm going to leave it alone and see just how big it can get.

UPDATE: September 25th: Yes, it's officially larger than a volleyball.