A hand lens may be needed to see the short cornicles of some species. These cornicles apparently are the ducts of glands that produce alarm odors. Aphids may be winged or wingless and colonies often have both forms. Aphids excrete a sugary liquid called honeydew. This honeydew drips onto plant foliage or other structures and provides a suitable place for black sooty molds to grow.
Ants often tend or care for aphids in return for the honeydew.
Therefore, if ants are running over a plant, look carefully for aphids. Each plant reacts differently to aphid attacks. Occasionally, aphids may actually kill leaves or small shoots. Since aphids may move from one plant to another, they may transmit plant diseases which contaminate the sucking mouthparts. Probably the most common disturbance caused by aphids is their never-ending production of honeydew.