I noticed these white masses of woolly alder aphids on alder plants on the edge of a wetland. Intrigued, I decided to do some research. Woolly alder aphids are parasitic on alder and maple trees, forming colonies and sucking the sap from the stems. They produce white fuzzy fibers that make them highly visible, but also unappealing to predators. Woolly alder aphids require alder and silver maple trees to complete their life cycle. Wingless aphid nymphs are born on silver maple trees in spring, where they feed on new leaves. For most of the summer woolly alder aphids are wingless and asexual. However, by mid summer, some individuals develop wings and begin to reproduce sexually, and fly to nearby alder tree to start new colonies, which are comprised of aphids in all developmental stages. Wingless aphids will overwinter on alder trees, where they produce female clones asexually. Some winged aphids find their way back to silver maple trees, where they lay eggs that overwinter in the cracks of the bark.

More details available here: https://www.ces.ncsu.edu/depts/ent/notes/O&T/trees/note06/note06.ht…