Woolly Alder Aphid. Plump and blue-black, but completely covered with white waxy filaments. Silver maple is the primary host, but they migrate to alder in mid-summer, then return to silver maple in late fall. This aphid is not particularly injurious to either host, but it becomes a nuisance when waxy filaments accumulate under heavily infested trees. Also, Woolly Apple Aphid, Rosy Apple Aphid, Pea Aphid, Cabbage Aphid, Bean Aphid, Mellon Aphid, Snowball Aphid, and many, many others.
Some aphids cause galls.
Witchhazel Cone Gall Aphid, Spiny Witchhazel Gall Aphid, and the Elm Cockscomb Gall Aphid. Natural enemies play a very important part in controlling aphid populations. Lady beetles, lacewings, damsel bugs, flower fly maggots, certain parasitic wasps, birds, and fungal diseases all attack aphids. Without them, these pests would be much more destructive. Gardeners should avoid unnecessary use of insecticides which are harmful to beneficial organisms.