Hey, thanks a lot for the explanation. You are a proper expert :)
Do I understand right that the oak in this case envelopes the parasite and that the sphere is actually this envelope? Next time I find this kind of egg I'll open it :)
Have a great Sunday.
!invest_vote
Yes, you understood correctly :) yea I see a lot of these on our oaks, so I googled awhile back what it is. But usually they like smaller trees for some reason. Or maybe the big ones are too high to see :)