On sunny fall afternoons, it sometimes looks like it is snowing. But it’s not snow …it’s the annual fall swarming of woolly aphids. These insects are really small. If it were not for their wooly appearance, you might not notice them at all. Their appearance comes from white, cottony wax filaments they produce from special glands that make them appear like a small, flying cotton ball. This wax helps prevent them from drying out, protects them from predators and also makes it easier for them to slip through and around plant hairs. There are many different species of wooly aphid, each specific to a host tree. They inhabit alder and maple trees, ash trees and birch trees. Photo by Heather McKee on 9/29/19 in Missoula, MT.