Scale insects feed by sucking sap from trees and shrubs. Sap feeding by scale insects may cause yellowing or wilting of leaves, stunted growth or unsightly appearance. Eventually scale insects may cause the death of all or part of the plant when infestations are heavy. Weakened plants may lose vigor and become more susceptible to injury caused by drought, severe winters, attack by other insects (such as borers), or infection by diseases. While feeding scale insects excrete a sweet, sticky substance called honeydew. Honeydew is a mixture of undigested sugar and water passed during digestion and deposited onto leaves and stems. Honeydew may make the plant appear shiny and wet and also attracts flies, ants, bees, and other insect scavengers. The honeydew may encourage a fungus called sooty mold. Honeydew can also cause a mess on sidewalks, cars, and houses beneath scale-infested trees.