large gall on twig on pool margins. Species of tree unknown but possibly oak
No interactions present.
Yes, this is the agamic generation gall of Andricus kollari, the marble gall.
This is on my local patch, a lot of the oaks in the Sandwell Valley are Quercus X rosacea, the hybrid between Q. robur (English or pedunculate oak) and Q. petraea (sessile oak).
Lat/Lng: 52.5, -2.0
OS grid ref: SP0292