Spangle galls are normally seen in late summer or early autumn on the underside of oak leaves. They are caused by the female gall wasp Neuroterus quercusbaccarum. A single leaf can have up to 100 of these galls, each containing a single developing larvae.
In early autumn the ground below some oak trees can be littered with fallen spangle galls. The larvae continue to develop inside, and in spring the females emerge to lay their eggs on the oak catkins.
These produce 'Currant galls', which hang like redcurrants. In summer the adult sexual generation will emerge from these and lay their eggs on the undersides of the oak leaves.
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