The maple eyespot gall is caused by a small midge. The fly lays its eggs in the undersurface of the leaves. The maggot that hatches develops quickly and produces a growth regulating hormone that causes the bright red and yellow rings around the gall, usually in June. The maggot inside the gall completes its development in about 10 days, drops to the ground to pupate, and transforms into an adult. There is only one generation each year and there is no control necessary. The galls generally do not harm the tree.