Gall size 2-4 mm.
These fairly large and hard galls form sparsely on Field Maple (Acer campestre), and are caused by the gall mite (Aceria macrochela). They are normally found near leaf veins which can cause some leaf deformation, and are green to begin with, gardually turning red where exposed to the sun.
During the autumn the adult mites escape through pores beneath the leaf and overwinter on the twigs.
Seen during the summer months, it is a common and widespread species. Native to Britain.