Dozens of species of aphids (plant lice) may be found on shade trees and woody ornamental plants in Colorado. Aphids feed on plants by sucking sap from the leaves, twigs or stems. Most aphids excrete large quantities of a sweet, sticky substance called honeydew. Aphids cause little damage to aspen, removing sap but rarely affecting overall plant health. Many kinds of insects naturally prey on aphids, most common are various species of lady beetles (ladybugs). When aphids are exposed on leaves, use of contact insecticides and soaps are helpful. When aphids have curled the plant leaves, use of systemic insecticides are more effective. For more information on aphids, see fact sheet Aphids on Shade Trees and Ornamentals.