Woolly Aphids: White Dancers of the Woods

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    Once when I was hiking in a forest near my home, I spotted a patch of bobbing white tufts on the branch of a tree. I first thought it was some sort of fungus and bent closer to investigate it. Already mystified at this strange sight, I was even more curious at the gray puddles covering the plants and leaf litter below the branch. This waving spectacle turned out to be a group of insects that twitch their abdomens when they are alarmed, as if they are hoping to distract predators with their rhythmic dancing and escape attack. These insects are called woolly aphids and belong to the family Aphididae in the order Hemiptera (UWM, 2014). The filaments that look like wool, which inspired their name, are made of wax that the aphids secrete from glands on their abdomens (UWM, 2014). The waxy fluff protects the aphids by deterring predators, while also repelling water off of them (UWM, 2014). Masquerading as white fluffy fungus helps the aphids to camouflage themselves from predators and humans alike. When I saw the aphids from a distance, I certainly did not expect to find insects under the fluff.
Woolly aphids (UWM, 2014)

        Woolly aphids feed on a variety of plants, including elm, alder, maple, apple, and serviceberry (Hahn, J. & Wold-Burkness, S., n.d.). Aphids are named for the group of plants that they frequently feed on. If you find woolly aphids on an elm tree, it is possible that they are woolly elm aphids. Another example is the woolly alder aphid, which feeds on the sap of silver maple and alder trees (Hahn, J. & Wold-Burkness, S., n.d.). Most woolly aphids rely on two host plants for feeding and reproduction during their life cycle. A female aphid will lay eggs on the first host in the fall, and the eggs will overwinter to hatch in the spring. These females, once mature, will then have live offspring. The offspring will feed until they are adults with wings, when they will fly to another plant to reproduce and begin the cycle again.

Woolly Apple Aphids (University of Maryland, 2021)

            The sap that the aphids ingest provides them with nutrients but also contains a very high amount of sugar (Hahn, J. & Wold-Burkness, S., n.d.). Instead of storing extra sugar like humans do, the aphids have a different solution: produce a sweet, sticky substance called honeydew. Honeydew drops from the aphids and coats anything beneath them, making it obvious that a tree has aphids on it. Other signs of an aphid infestation include curling or yellow leaves and inhibited growth (Hahn, J. & Wold-Burkness, S., n.d.).

Aphid Honeydew and Sooty Mold (Lewis, 2012)

           Even though aphids suck sap from plants, they are not a serious pest. Many plants can continue to thrive while hosting aphid infestations, so the more common problem is the mess that results from honeydew. Honeydew is very frustrating for owners of cars and patio furniture, which can become covered in honeydew. On top of the stickiness, honeydew attracts ants and yellow jackets that feed on the sugar. A fungus called sooty mold can also grow on honeydew, turning the sticky coating into a gray carpet (Hahn, J. & Wold-Burkness, S., n.d.).

Sooty Mold (UWM, 2014)
    Other than visual frustrations, woolly aphids do not pose a serious threat to plant populations or humans. Many state extensions do not recommend any treatment, since common pesticides do not kill woolly aphids easily. Woolly aphid populations are also controlled by predators like lacewings, ladybugs, and parasitic wasps (UWM, 2014). The aphids’ disguise is not completely foolproof, after all. If you ever see a branch covered in white fuzz, take a closer look—you might get to enjoy a natural version of choreographed dance.

Works Cited

Hahn, J., & Wold-Burkness, S. (n.d.). Aphids in home yards and gardens. University of Minnesota Extension. Retrieved from extension.umn.edu/yard-and-garden-insects/aphids#managing-woolly-aphids-347963

Lewis, D. (2012, June 27). Woolly aphids -- interesting but messy. Horticulture and Home Pest News. Retrieved from hortnews.extension.iastate.edu/2012/6-27/woollyaphids.html

University of Maryland. (2021, June 2). Woolly aphids on trees. University of Maryland Extension. Retrieved from extension.umd.edu/resource/woolly-aphids-trees

University of Wisconsin Milwaukee. (2014, August 5). Woolly alder aphid (family Aphididae). College of          
          Letters & Science. Retrieved from uwm.edu

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