The Living Forest (151) : Oak Marble Galls

The Living Forest (151) : Oak Marble Galls

Galls are abnormal outgrowths of plant or tree tissues and can be caused by various parasites, mostly by insects like gall wasps and gall flies, but also some fungi, bacteria and mites can be the origin.

Gall insects lay their eggs on the leaf surface or on the buds of young twigs and at the same time secrete a chemical that causes the cells on the infected surface to expand and grow over the eggs forming the gall.
The larvae then feed inside the gall until fully grown, completely protected against predators, cold and rain.

Galls are not really spectacular, but some are beautifully shaped like these Marble Galls (coming from a gall wasp) growing on Oaks.
Fortunately, galls caused by insects are harmless to the tree.

Dutch name : Eikengal (ook knikkergal genoemd)
German name : Schwammkugelgalle
Latin name : Andricus kollari

Another gall species can be seen here