Oak Marble Gall Wasp

Oak Marble Gall ©Philip Precey

Oak marble gall wasp

Scientific name: Andricus kollari
The oak marble gall wasp produces brown, marble-shaped growths, or 'galls', on oak twigs. Inside the gall, the larvae of the wasp feed on the host tissues, but cause little damage.

Species information

Statistics

Diameter of gall: up to 2cm

Conservation status

Introduced species.

When to see

January to December

About

The oak marble gall wasp, Andricus kollari, is a tiny wasp that causes galls on oak leaves. Clusters of oak marble galls (also known as 'oak nuts') 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

The oak marble gall wasp produces hard, woody, marble-like balls that can be found on oak twigs, often in clusters.

Distribution

Widespread.

Did you know?

The closely related Andricus fecundatorcauses 'artichoke galls' on oak buds, so-named for their distinctive shape and look. Each 'artichoke' is inhabited by a single larva in a hard casing that is released in autumn. The adults emerge in spring.

How people can help

The Wildlife Trusts record and monitor our local wildlife to understand the effects of various factors on their populations, such as the introduction of new species. You can help with this vital monitoring work by becoming a volunteer - you'll not only help local wildlife, but learn new skills and make new friends along the way.