Eriophyoid mites (erios for short) are the smallest of all mites, with adults around 0.5 mm long. Their small size makes it difficult to spot them in the field, even with a good hand lens. They are sporadic pests that cause serious damage during outbreaks. Usually, erios are found because of the symptoms they cause – bud deformation, rusting or galling, depending on the species. Some erio species live on plants without causing symptoms at all.