The Oak Marble Gall (also known as 'Oak Nut') is caused by a tiny gall wasp, Andricus kollari. Clusters of Oak Marble Galls can be found on oak twigs. They turn brown as they mature and emergence holes, from which the asexual adults have escaped, can be seen from autumn onwards. The empty gall is left on the twig. The emerging females then lay eggs in the buds of Turkey Oaks which develop overwinter and emerge in spring as a sexual generation of males and females, ready to make the familiar summer gall.
How to identify
Oak Marble Galls are hard, woody, marble-like balls found on oak twigs, often in clusters.
Where to find it
When to find it
How can people help
The Oak Marble Gall was introduced into the UK in the 1800s from the Middle East. Despite concerns about the Oak Marble Gall affecting populations of our native Oaks, there have not been any serious consequences yet. The Wildlife Trusts work with surveyors, scientists and other conservationists to monitor changes in our native wildlife to determine the effects of environmental change, such as the introduction or spread of non-native species. You can help: volunteer for your local Trust and you'll be able to take part in surveys, adding to a growing bank of data.