Yeah, its odd I have so many and you haven't seen any. I'm playing the Default world type and my base is on the border of a taiga biome and a Lush Redwoods biome. From my small base I can see 12 of those spheres, and they are each 13 blocks across sooo..... lol. Anyway I've disabled the drowning creepers so I won't see any more of them in my world. I just thought you might want to know about it.