Yet another gall

It's that time of year, so no apologies for posting a photo of another plant gall - this time one of the more spectacular ones, but a recent immigrant. The Knopper Gall develops on acorns, triggered by the gall wasp Andricus quercuscalicis, and can destroy a lot of the acorn crop in some years. It is a relative newcomer to the UK oak trees, having arrived sometime in the 1960s. Indeed, I looked it up in one of the great little books on galls, Arnold Darlington's 'Pocket Encyclopaedia of Plant Galls' (1968) and there is no entry, despite plenty of references to other species of the genus Andricus, which also induce galls on oak trees.