I passed a European alder tree (Alnus glutinosa) on Willow Path at the Arnold Arboretum a couple days ago (accession 1399-73*B), and noticed that many of its branches were covered in a white fungus/mold-like substance. Upon closer inspection, the mold moved!
This was no mold. It was an infestation of woolly alder aphids (Prociphilus tessellatus).
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