eat and strip newly emerging leaves. This weakens the trees which then must expend more stored energy to replenish lost leaves.
attack just about every plant in your landscape and can only be controlled with an oil or soap spray. The sooner they are controlled in the spring, the better off your plants will be all season. Scales
do a number on ornamental fruit trees, as well as azaleas, taxus, pine, hemlocks, etc, etc.