A tiny mite produces the pimple-like spots on the leaves of Field Maple (Acer campestre). Each pustule measuring between 1-3mm high 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.
Photographs of Aceria myriadeum, taken June 2013, local wood and nature reserve. © Pete Hillman 2013. Camera used Nikon Coolpix P500.