An oak apple gall.Q: We have these golfball-sized green pods attached to our oak tree. It appears to have some sort of seed within the pod. I always thought that from acorns grow the mighty oak. What are these?
A: Those growths aren't oak seeds but the housing structure of a tiny wasp. They're called oak apple galls.
A single wasp larvae is at the center of this protective pod, which grows a spongy mass with tentacles that makes it resemble some sort of round fruity structure.
The growths and wasps aren't harmful, so you could just be fascinated and then ignore it. Or you could pick off the galls and destroy them if you're concerned about the looks or more of them appearing in future years.
No need to spray anything.