25th May 2025

These small red lumps on the surface of young sycamore leaves are caused by the Sycamore Gall Mite (Aceria cephalonia). The mite is only a fraction of a millimetre long and over-winters in bark crevices. When new leaves appear in spring, the mites begin feeding on cell juices. This damage prompts the leaf to produce the galls. In mid-May, the mites lay eggs in the galls and several generations are produced before leaf fall.

Sycamore Gall Mite