One common group, woolly aphids, produce an abundance of flossy, waxy threads that cover their bodies. Aphids feed on plants by sucking plant sap from the leaves, twigs or stems of plants. When abundant, aphids remove large quantities of sap, reducing growth and vigor of the plant. Aphid feeding on developing leaves also can produce leaf curl injuries. This is most frequently observed on snowball viburnum, honeysuckle, plum and ash.
Most aphids also excrete large quantities of a sweet, sticky substance called honeydew.
At times, excessive honeydew dropping from trees can be an extreme nuisance. Also, sooty mold fungus may grow on the honeydew, producing a gray, unattractive covering of the leaves. Ants often are attracted to honeydew and feed on it. Often the presence of ants crawling up trees or over foliage indicates that large numbers of aphids or other honeydew producers also are on the plants.