These lovely beetles can spend their entire life cycles living off of a single poplar or cottonwood tree. Females lay their eggs in clusters on the undersides of leaves. Those eggs hatch and the larvae begin feeding on the leaf tissues until nothing but a skeleton of veins remains. Then, they pupate into adults which will continue the process of defoliating the tree by eating the thick veins and midribs left behind by the larvae. Some small saplings can be killed by a particularly hungry population of breeding Cottonwood Leaf Beetles. This species may not be present in the PNW west of the Cascades. If you discover them there, please let me know!