Underneath the white waxy threads are many bluish-black aphids. This is the woolly alder aphid. This insect is widely distributed in the U.S. and Canada.
Silver maple is considered the primary food plant and alder the secondary or alternate food plant.
The woolly alder aphid is not generally of great economic importance. The aphids feed by sucking plant juices from the leaf and twig tissues. Young branches may be retarded slightly following heavy attacks on alders. The leaves of silver maples infested with this aphid develop a tendency to droop, fold, or double downward around the colony. This does not appear to greatly interfere with the function of the leaves.