These artichoke galls began to form earlier this summer when a female gall wasp Andricus fecundator laid a single egg in each of the terminal buds of this branch of a sessile oak.
Artichoke galls are also known as larch-cone galls or hop galls. The larva develops protected by the overlapping scales.
An adult female will emerge in the spring to lay her unfertilised eggs in the emerging catkins of the oak. The alternate summer generation of male and female gall wasps will emerge from the resulting hairy catkins galls in May or June.
This sessile oak was growing on the embankment of the disused colliery railway which formerly connected Hartley Bank to Addingford, crossing the canal and river en route.