Oak leaf underworld

Silk button galls on the underside of an oak leaf.
They are created when a tiny wasp lays its eggs in the leaf bud. Via a chemical response, these structures, each just a few millimetres across, are formed to accommodate the wasp larvae. Hundreds of them can cluster on the underside of the oak leaves where, hidden from view, they will remain even after the leaf has fallen,  the larvae only hatching into adult gall wasps in early spring. Does the tree derive any benefit from gall formation or is it more a case of damage limitation? I don't think we have the answer yet.

The galls are named from their likeness to old-fashioned handmade silk buttons something like this. I was delighted when I enlarged the image to find that I had captured a minuscule bug,  which looks like an aphid, clambering over one of the buttons  in this mysterious underleaf underworld.