oak-marble gall A dark brown, hard, spherical gall on Quercus robur formed by the sexual generation of the gall wasp Andricus kollari. The galls contain members of the unisexual generation (all females) which emerge in spring to form ‘ant-pupae’ galls on the axillary buds of Quercus cerris (Turkey oak). The insect was introduced to Britain in 1830 for use in the dyeing and ink industry, the galls containing up to 17 per cent dry weight of tannic acid.

oak-marble gall A dark brown, hard, spherical gall on Quercus robur formed by the sexual generation of the gall wasp Andricus kollari. The galls contain members of the unisexual generation (all females) which emerge in spring to form ‘ant-pupae’ galls on the axillary buds of Quercus cerris (Turkey oak). The insect was introduced to Britain in 1830 for use in the dyeing and ink industry, the galls containing up to 17 per cent dry weight of tannic acid.