The galls are caused by the larvae of a small gnatlike midge, Dasineura communis (Felt). These galls can completely crumple the early leaves of maples, often making them look like herbicide damage. The maple gouty vein gall midge attacks only sugar maple and causes thickened pouches along the major veins. These conspicuous, hairlike patches may resemble a fungus or a disease. Crimson to yellow, velvet-like patches form on the upper and lower leaf surfaces as a result of mite feeding activity. This colorful gall is caused by another eriophyid mite, Eriopyhes spp. The maple velvet erineum gall is another gall commonly found on maples, primarly silver, Norway and boxelder maples. These galls rarely distort the leaf, but considerable numbers of galls can make the leaves unsightly. The gall appears as thin, elongate bladders arising from the upper leaf surface. This gall is caused by the mite, Vasates aceriscrumena (Riley). On sugar maple, another leaf gall is commonly found, the maple spindle gall. Leaves frequently become so covered with the galls that they completely twist out of shape and may even drop early. At first the galls are green, but they quickly turn pink to red and eventually black. The structures are generally noticed first in May, about the time the leaves have become fully expanded. These are maple bladder galls caused by a small eriophyid mite, Vasates quadripedes (Shimer). The upper surface of silver and red maple leaves often become covered with small, red, round wartlike structures about 1/16- to 1/8-inch in diameter. The enveloped arthropod feeds and reproduces from within the gall. The plant responds by increasing the production of leaf tissue, thereby enclosing the individual mite or insect. The abnormal plant growth is stimulated by a combination of plant hormones and hormones introduced into the plant during arthropod feeding. Galls are plant structures that form as a result of arthropod feeding.
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