In a scrubby field in St Leonards-on-Sea, East Sussex I found these cola nut galls (Andricus lignicola) yesterday growing on some young oak trees. The trees were most probably the hybrid (Quercus x rosacea) between pedunculate oak (Quercus robur) and sessile oak (Quercus petraea), not that I think this is of any significance so far as the galls are concerned.
They are caused by a small wasp and chemicals injected by the female at egg-laying time induce the galls to form, thus providing food for the larvae. The cola nut is a plant from tropical Africa and there is only a very superficial resemblance between it and these galls.
Although described as widespread and common, I have been unable to find any earlier Sussex records and, though seemingly not so frequent as the marble gall, I am sure it is overlooked rather than rare.
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