The top side of the leaves of infested plants are usually coated with a shiny, sticky substance known as "honeydew," the partially digested excretions of the aphids. The honeydew provides a medium for the growth of black sooty mold, a fungus which gives the leaves a dark, dirty appearance.
New leaf growth is often undersized and/or wrinkled.
The undigested sugars of the honeydew attract ants to the leaves of the plant, causing the impression that the ants are the problem.
In small numbers, aphids do not cause much damage, and can be easily removed by spraying the underside of the leaves with a stream of soapy water under moderate pressure. But a small infestation can quickly get out of control. If left unchecked, aphids can defoliate a tree.
Aphids cluster on the underside of infested plants. The soft-bodied insects cause damage to plants by sucknig the juices from the leaves.