Appreciating Dancing Aphids
One of the main principles of ecological gardening is to work with nature not against her. So to successfully create a garden that is an oasis for all forms of life, we must somemtimes change our way of thinking toward inhabitants we may consider less desirable.
Aphids are often bemoaned because they feed on the sap of their host, penetrating the phloem layer, which could result in the decline of plant vigor. Last week, we came across a few beech trees infested with aphids. Knowing that aphids usually specialize on one kind of plant, it was easy to determine that we were seeing the beech blight aphid (Grylloprociphilus imbricator). At first glance it may be alarming to see branches of a mature tree completely covered with these aphids [or any insect for that matter] but it is wise to consider how host plants and insects work together to provide value in the ecosystem.
American beech (Fagus grandifolia) trees are the primary host of these native aphids, where they can be found from spring through fall. The aphids migrate to their secondary host, bald cypress trees (Taxodium distichum), where they colonize the roots. I was fascinated to learn about an insect that uses two host plants. In fact in one of my favorite insect guides, Whitney Cranshaw's 'Garden Insects of North America' there is an entire page of aphids that commonly alternate between a primary (winter) and secondary (summer) host.
Females give birth to daughters without mating, allowing them to build up their numbers quickly. By late summer / early fall they reach their peak population. They then begin to produce winged males and females, allowing them to disperse, mate and lay eggs that overwinter often on a second host.
Aphids that develop on the beech trees produce profuse wax fibers from their abdomen that give them their woolly appearance. The idea is that the wax acts as a shield so when a predator bites into them all they get is a mouthful of fluff.
These aphids are also known as boogie-woogie aphids because when their colony is disturbed, the nymphs wiggle around warning predators not to engage. You can see them in motion on my YouTube channel
They can be highly aggressive toward predators and will mass attack using their piercing-sucking mouth parts. If you unintentionally brush up against a branch covered with these aphids it could feel like they were biting you.
If you have read this far, I appreciate you sticking with me. I realize I may be the only one fascinated by these creepy crawlies. But now, to the good part.
These aphids are native to our area and serve as a significant food source for two creatures that many gardeners would welcome in their gardens: the harvester butterfly and Tennessee warbler.
|photo courtesy of University of Florida|
Harvester butterflies have a short proboscis that they use to sip on the aphid's honeydew and tree sap. Therefore, you won't see these beauties at your flowers. Adult butterflies stay close to their caterpillar's food sources and for this reason they exist in very localized populations.
The female butterflies lay their eggs on clumps of aphids. The caterpillars hatch out and begin to feed on the aphids, specifically the woolly alder aphids and beech blight aphids. These caterpillars develop faster than other butterfly species because of the concentrated nutrients provided by the aphids. Whereas most butterfly species complete 5 instar stages the harvester only takes four.
The Tennessee warbler is a generalist aphid predator. The beech blight aphids emerge in March just as this warbler leaves its wintering grounds and migrates through North Georgia. In late August when the warblers begin their fall migration the aphids are at their peak population numbers. This timing is significant because aphids are a key prey species providing an abundant food resource for these birds just when they need it most.
The aphid colonies also attract flies, bees, wasps and other insects that enjoy sweet liquids. The black sooty mold that grows on the honeydew secreted from beech aphids can build up, but not to worry, because neither the aphids or the mold is detrimental to beech trees. If you find them unsightly just spray the aphids off the branches with a hose.
More importantly if you are fortunate to have a wooded area, especially near water, you may find a colony of these aphids and consequently the harvester butterfly and Tennessee warbler that rely on them.