I have lived at my house for 5 years in Guildford in Surrey, I have a very large old oak tree at the bottom of my garden.
I have always noticed sap dropping from it. The sap in not water soluble and soap in needed to removed it. When i park the car underneath it it can be covered in at least an hour.Wasp in the area seem to love the sap and will continue to feed on it even while we are driving around.
This year i have noticed that most of the acorns that have fallen from the tree have a mass of, i presume, chewed wood that has been formed into a outer-like shell. This has never happend in previous years. It is very sticky like the sap that falls from the tree. The outer shell looks quite spikey. When i tried to break one of them open i found it very tough. When i suceeded i found the shell was made of wood and the acorn inside was gone. In it's place was a very small white bead like "egg" aproximately 3mm long. When i broke this open i found a white grub.
Do you have any information on this or what it may be and is it harmfull? Any inormation you have would be greatly apreciated. Thank you very much.