Spangles and currants - very galling

Some of our oak trees are now showing yellow blotches on their leaves.

 

If you look underneath the leaves you find lots of little brown sequins.  These are spangle galls and are caused by a tiny gall wasp called Neuroterus quercusbaccarum. 

 

They fall to the ground in autumn when the leaves fall, and in the spring fertile female wasps emerge and lay eggs on oak buds. These cause not spangle galls but red currant galls on the young oak leaves and catkins in May and June. 

 

Photo: wyreforest.net

 

This time both male and female wasps emerge from the galls and this results in eggs laid on the oak leaves. These cause the new spangle galls.