Owing to the prevalence of a number of scale insects in various parts of the state, and as the majority of inquiries regarding insect pests which now reach the Experiment Station are concerning members of this group, a brief bulletin on them has been deemed advisable. Scale insects, or bark-lice as they are commonly called, are well known to all fruit growers. Papers and works which enable one familiar with entomological terms to distinguish the different species are readily obtainable. However, an article which will describe in as simple and ordinary terms as possible the more economically important species of our state will, it is hoped, be a material aid to horticulturists and others interested in the cultivation of fruits and ornamental trees and shrubs.