Galls

These disc shaped galls clinging to an oak leaf belong to a species of wasp. If they are the Neuroterus quercusbaccurum wasp they have a complicated life cycle.
The adult wasp forms these discs to envelope their young which grow and then drop to the ground to feed under the leaves. They are all female and can reproduce without mating and so when they have matured into wasps they lay their eggs in the buds of the oak tree and produce a "currant" gall on the catkins and leaves. From these the males and females emerge, mate, and lay their eggs on the underside of a leaf producing disk galls and so the cycle continues! Why are they so complicated I wonder?!