Oak Apples

I found oak apples - oak galls - galore
On oak hedgerows! But what were they for?
A gall wasp laid an egg
In a leaf bud, which led
To a larva, and left the oak sore.

by Moi

The female gall wasp (in the family Cynipidae) lays single eggs in developing leaf buds. Chemicals injected by the larva cause an oak apple to develop. The larva then feeds on the gall tissue.

If you have a look on Wiki, there's interesting folklore relating to oak apples and what you find inside one of Michaelmas Day! And apparently 'Oak Apple Day' (or 'Royal Oak Day') was once a Public Holiday in England - on 29 May - in celebration of the Restoration of Charles II in 1660.

Thank you for all the lovely comments on my feathery yesterblip.