OAK STUFF

This year's developing acorns (above) should not be confused with the marble galls (below) caused by the oak's reaction to an egg-laying gall wasp.

The marble gall is smooth and spherical. 

 And while the acorns fall off the tree in late summer, the marble galls may persist into the following year.  You can see the tiny exit hole where the new generation gall wasp exited its first home.

Young oak saplings seem to be favoured by these mini-wasps

More mature oak trees are blessed with knopper galls on the acorns and spangle galls on the leaves.