What causes this acorn disease? This year, many acorns in our area (Germany, Schartzwald) fell prematurely, plagued by some kind of warts or gall-nuts which I see for the first time: ![enter image description here]( ...--prophetes.ai

What causes this acorn disease? This year, many acorns in our area (Germany, Schartzwald) fell prematurely, plagued by some kind of warts or gall-nuts which I see for the first time: ![enter image description here]( image description here]( Some of the acorns are covered by two or three warts at a time, so that the actual nut itself is practically non-existent. Judging by the hole present in all the warts, I'm guessing those were houses for some insects or larvae. Unfortunately, warts on acorns available for inspection (those which already fell) are already abandoned by their hosts. Does anyone know who those guys are and how they look like?

The structure on the oak nut is a knopper gall.

> It is a distortion of growing acorns on pedunculate oak (Quercus robur L.) trees, caused by gall wasps( _Andricus quercuscalicis_ ), which lay eggs in buds with their ovipositor.

![Image1](

An _Andricus quercuscalicis_ larva in an open gall of an acorn: Link

Here's a video by BBC on the same you may find it interesting.