Someone approached me last week with a question regarding some fuzzy looking growths on the leaves of the shingle oak (Quercus imbricaria) growing just inside the Visitors Cottage entrance to the garden. Fuzzy oak gall is created when a tiny wasp lays tons of eggs in the leaf tissue of oak trees in early spring. The wasp feeds and develops all summer long, maturing in the gall, and emerges later to continue the life cycle.
Galls are an interesting plant/insect interaction. Little is still known about how gall wasps induce abnormal cell growth around the eggs being laid. Interestingly, gall formation is a common plant defense response to invasion. Plants often compartmentalize, walling off wounds and infections to limit feeding or spreading infection. Bacteria, nematodes, mites, flies and wasps are all known to create galls on various plant parts. In the case of fuzzy oak gall wasp, the gall protects the wasp larvae during a vulnerable developmental stage.
Another interesting thing I learned while digging up info on all this delicious biological factiodness (Yes, I just made up a new word, save it in your dictionary), are all the parasites and predators who love this gall action. There is another group of wasps, for example, who search out galls to insert their own eggs into to feed upon the now cornered wasp larvae.
Amazing interactions like galls and gall parasitism are occurring every day around us. Oaks host over 400 different species of insects, all of whom rely on this all important genus for their life cycle. Planting native trees with linkages to these insects supports a larger ecosystem. As gardeners, we often stress out when seeing insect damage to our Better Homes and Gardens picture perfect plants. Most of the time, galls like fuzzy oak gall do no lasting harm to the host plant. They may appear “unsightly” to the gardener, but perhaps the gardener just needs to shift their paradigms. A plant free of any imperfections is one type of beauty, but a plant linked to a larger context, part of a bigger world, playing host to all kinds of amazing ecological interactions, is another kind of beauty. I struggle to shift my perspective all the time and try to remember to look at the world differently, that perhaps an imperfect plant is not so galling after all.
Josh Steffen, Horticulture and Facilities Manager