Have you noticed them, these galls on the acorns?

During our walks on Broadwater Path in Weybridge, we noticed them hanging in the oak trees, and first, it looks like the oak bears strange fruit, but they were actually ‘ornamental’ growths where the acorns should be. They are formed by a tiny gall wasp species, Andricus quercuscalicis, the Knopper* oak gall wasps, inoculating the embryonic acorn buds with their eggs. Inside the knobbly galls, or growths, the larvae of the wasps feed on the host tissues. The Turkey oak, Quercus cerris, is host to these wasps. Interesting is that most of our native British oaks grow where Turkey oaks were planted on country estates since the 1730s.

Oak trees infested with these galls, may also show symptoms in the leaves, such as browning and dead tissue beyond location of the gall. In general, the trees’ health is not affected by these growths. While leaves may drop prematurely or become distorted, the galls are usually only a cosmetic problem.

Happy walks, Pimm + Marcel 😉


* Knopper from ‘knop’. From Old English ‘cnoppa’ to ‘knop’ in Middle English, meaning ‘an ornamental knob’.