Woolly alder aphids congregate on alder stems to spend the winter. / Photo Credit: Ryan Brown, Vilas County Forest

By Linda Williams, DNR Forest Health Specialist, Woodruff
Linda.Williams@wisconsin.gov, 920-360-0665

Woolly alder aphids spend their winters on alder stems and summers feeding on maple leaves. Large congregations of these aphids can be visible from a distance, and the bright white patches of aphids may catch your eye.

These plump bluish aphids, with white fluffy growths on their abdomens, are called woolly alder aphids when they’re found on alder – and maple blight aphids during the part of their life cycle when they’re feeding on maples.

When feeding on maples, they can produce tiny drops of honeydew that will drip onto whatever might be under the tree (houses, vehicles, children’s toys, etc.), and sooty mold can grow on this sweet, sticky honeydew.

By this time of year, the aphids have developed wings to enable them to migrate from maple to alder, where they will cluster into groups to spend the winter.

Ants defend helpless woolly alder aphids against a predatory lacewing larva, sometimes called an aphid lion. / Photo Credit: Ryan Brown, Vilas County Forest

Groups can be very large, but their presence doesn’t significantly damage alder. Significant damage to maples is also uncommon.

Aphids, including woolly aphids, have several predators that help keep populations in check. One of the photos with this article shows ants defending aphids against a lacewing larva. Ants like to feed on the honeydew produced by the aphids.

Insecticides are not usually necessary against aphids because damage is not common. If the white fluffy stuff bothers you, a strong spray of water will wash the aphids off and can kill many of these soft-bodied insects. Sooty mold should be washed off periodically and may require some scrubbing to remove.