Class Arachnida: Arachnids » Order Prostigmata » Family Eriophyidae: Gall Mites » Aceria aceriscampestris (Nalepa, 1922)
Height 1-3 mm.
A tiny mite produces the pimple-like spots on the leaves of Field Maple (Acer campestre). Each pustule may contain several mites. The galls maybe fairly prolific, covering leaves almost in their entirety.
The mites leave the gall through tiny holes in the underside of the leaf in autumn and overwinter in fissures in the tree bark. Seen summer until autumn. Common and widespread.