One of my sharp-eyed young friends from yesterday found this, not quite rolling around, the little stem had restricted its mobility.
It is an oak marble gall, probably made by the tiny gall wasp 𝐴𝑛𝑑𝑟𝑖𝑐𝑢𝑠 𝑘𝑜𝑙𝑙𝑎𝑟𝑖. It lays an egg in a developing oak bud and, rather wonderfully, persuades the oak to build this hard spherical structure around its developing larva. The gall is therefore neither fruit nor seed, but oak tissue hijacked by an insect.
Eventually the adult wasp emerges through a neat little round hole. All this effort by a mighty oak for a creature only a few millimetres long.
But these little balls have another story.
Oak galls are extraordinarily rich in tannins and for centuries they were collected to make iron-gall ink. Crush the galls, extract the tannins and add iron salts and you have an ink that was used across Europe for manuscripts, letters, official records and maps.
I had the memory of the word ‘gall’ in my mind when quizzed about it. Perhaps I haven’t quite ‘lost my marbles’ just yet.