The Knopper Gall is caused by a tiny gall wasp, Andricus quercuscalicis. It produces ridged outgrowths on the acorns of our native Pedunculate Oak; forming in August they are sticky and red, later becoming woody and brown. A second generation then develops in the catkins of Turkey Oak.
How to identify
Unmistakeable: the Knopper Gall is a nobbly, bowl-shaped protrusion from acorns.
Where to find it
When to find it
How can people help
The Knopper Gall arrived in the UK in the 1960s and spread rapidly. Despite concerns about the Knopper Gall affecting populations of our native Oaks (heavy infestations can cause poor acorn crops), 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.