Acorn Knopper Gall

Another macro scan - actual acorn is about 1.5cm in diameter :D "Andricus quercuscalicis is a gall wasp species inducing knopper galls. Knopper galls develop as a chemically induced distortion of growing acorns on pedunculate oak (Quercus robur L.) trees, caused by gall wasps, which lay eggs in buds with their ovipositor." - https://en.wikipedia.org/wiki/Andricus_quercuscalicis