Scales are so unusual looking that many people do not at first recognize them as insects. Scales have long piercing mouth-parts with which they suck juices out of the plant. They may occur on twigs, leaves, branches, or fruit.
Severe infestations can cause overall decline and even death of plants.
Most scales have many natural enemies that often effectively control them. Two groups of scales, the armored scales and the soft scales, are important woody plant pests. Common scales in each group are listed in the following. Excellent color keys for scale insects in California are available from the California Department of Pesticide Regulation. See the References for titles.