By Rich Niccum, Education Services Manager
As you walk the trails in early fall you may see white “fuzz” covering the leaves of beech trees. Upon closer inspection the fuzz looks alive, and that’s because it is! You are observing a fascinating insect called the beech blight aphid or the woolly beech aphid. This insect in the order Hemiptera forms dense colonies on small branches and the underside of leaves of American beech trees usually starting in mid-July. Heavily colonized tree branches and leaves appear to be covered with snow. As you observe the insect, touch the branch or leaf and watch what happens. The “snow” will appear to come alive as the aphids perform a defensive behavior by raising their posterior ends and swaying side to side. This action has also led the insect to earn the nickname the “Boogie-Woogie Aphid”. They gather en masse on the beech tree branches to feed, piercing the bark with their syringe-like mouth parts called stylets and sucking the sap out. The aphids do not usually damage the trees, but some die back may be seen on intensely colonized branches.
As you stand admiring the dancing aphids you may also notice that some of the leaves beneath them are covered in “soot”. Growing on the honeydew, or scat, that the aphids secrete is a fungus called Scorias spongiosa, also known affectionately as the beech aphid poop eater.This fungus is a sooty mold that grows in thin black layers on leaves, branches and the ground where the aphids have dripped their honeydew. The mold is not parasitic to the plant as it does not penetrate any part. It can potentially damage the plant by blocking photosynthesis, slowing growth and eventually hurting fruit or nut production, but the damage is usually relatively light. Some recent studies have suggested that the mold may actually be environmentally beneficial by removing more hydrocarbons and heavy metals from the air then clean leaves, thus more efficiently cleaning polluted air.
This sooty mold, unlike other species, is restricted to the American beech and the woolly beech aphid. Scorias spongiosa starts growing as a thin layer of yellow-brown tufts on the leaves and ground beneath the aphids. As more honeydew is secreted and accumulates the fungus grows larger and larger until it begins to resemble a large yellow sponge hanging off the tree. It even feels spongy. As the fungus grows thicker it blackens and becomes harder, eventually dying. Because the woolly aphids are so concentrated the fungus grows to a much larger size then most sooty molds. Some specimens can grow to the size of a football, but most average about 15 cm long. As you walk the trails this winter and into next spring scan the woods and you will most likely spot the very durable poop-eater fungus still hanging on the branches.
The relationship between the “Boogie Woogie Aphid” and the beech aphid poop-eater is one of those natural occurrences that goes unnoticed by many, but upon closer inspection is an incredibly fascinating part of our natural world. So next time you are out on the trail take a moment to notice the little things and marvel in the wonders of nature.