Utah State University Extension
Eriophyid mites are translucent, cigar-shaped microscopic mites that cause deformities on many plants species. These mites are noticed when their feeding causes abnormalities of plant tissues such as erineum, galls, brooms, leaf curling, blisters, rusts, silvering, fruit rusetting, and deformed buds, catkins, fruits, etc. Fortunately, these mites rarely cause serious harm to plants, and control is seldom needed. In fact, eriophyid mites can serve as an alternative food source for predatory mites when their primary food source is absent.
Davis, Ryan S. and Beddes, Taun, "Eriophyid Mites, Bud, Blister, Gall, and Rust Mites" (2011). All Current Publications. Paper 898.