The woolly elm aphid's activity creates the obvious little "snowballs" in our American elm varieties. These snowballs are a small cluster of leaves covered with a white wax secreted by the adult aphids. These aphids also produce lots of honey dew. The first sign of their activity is the curling of elm leaves. Later the snowballs appear, which with time become clusters of brown leaves. The adults themselves are 3 mm long, black with legs. The clusters of brown leaves usually persist during the winter. This insect does no measurable damage to the host elm Tree.
(Photo credit: “Woolly aphid" by Tmaq97, licensed under CC BY-SA 3.0.)
