Invertebrates
Marble Gall Wasp
Andricus kollari
On an oak twig in an English wood, a hard brown ball the size of a marble holds a developing wasp, and a neat round hole shows where last year’s adult escaped.
Overview
The marble gall wasp, Andricus kollari, is a tiny Mediterranean wasp whose larvae cause oaks to grow marble-sized galls, and which has become established in Britain. Its alternating generations and the use of its galls for ink make it a classic example of an insect that manipulates plant growth.
A wasp that builds its home out of a tree
By releasing chemicals that redirect the oak’s growth, the larva gets a hard, protected, well-fed nursery built entirely from the tree’s own tissue.
Status
Not Evaluated, but abundant on oaks.
Marble Gall Wasp: common questions
What is a gall?
It is an abnormal growth on a plant, in this case an oak twig, triggered by the wasp larva, which feeds and develops inside it.
Why was the gall used for ink?
Oak galls are rich in tannins, which react with iron salts to make iron-gall ink, the standard writing ink in Europe for centuries.
How does the wasp escape?
The adult wasp chews a neat, round exit hole in the gall in autumn.
Where is the marble gall wasp found?
It lives on oak trees across southern and central Europe, and has been introduced to Britain and other places.