BUCYRUS — Perhaps you have noticed weird, ball-like plant growths while hiking through a park or even in your own backyard.
These abnormalities growing on trees or other plants, called galls, are commonly formed by insects but are also caused by viruses, bacteria, fungi, or mites.
Insect galls are typically species-specific as well as tissue-specific, meaning the insect only lays its eggs on one species of plant (e.g., Pin Oak) and in one part of the plant (e.g., a leaf bud).
Unless it’s from a previous year, when you see a gall there is likely a tiny insect larva within it. The gall serves as the larva’s mini habitat, providing both food and shelter as it grows and pupates.
One of the most interesting and conspicuous gall formers are cynipid wasps. These miniscule wasps cannot sting and are likely to be mistaken as gnats, if you even notice them at all.
There are over 700 species in North America alone, most of which are oak specialists. Female cynipid wasps must time their ovipositing, or egg laying, during spring when cells within oak buds are rapidly dividing.
Along with the egg, plant growth regulators are injected, resulting in the abnormal growth of plant tissue that forms the gall. As the leaf or twig grows, so does the gall. The wasp larva eats, grows, and pupates inside, typically waiting until the following spring to emerge as an adult wasp.
However, some species of cynipid wasps have alternating generations, with a generation of wasps quite different in appearance (both galls and adults) than the “normal” generation. This first generation emerges in late June and consists of only parthenogenetic females—that is, females who can lay eggs without mating.
The larvae from these eggs then develop within “normal” galls, with both male and female adults emerging the following spring.
While it may seem as if these galls are ready-made fortresses — most of them are very hard and some are even covered in spikes — they are, in fact, popular snacks for other animals.
Larger predators include songbirds, woodpeckers, and squirrels. However, the succulent wasp larva tucked within a gall is more likely to succumb to predation by a fellow arthropod. Most frequently other wasps, but also moths and beetles, either prey on cynipid wasps or co-opt their gall space to use as their own.
Incredibly, one species of chalcid wasp, known ominously as the Crypt-keeper Wasp, can “mind control” its cynipid larval host. Upon hatching, the Crypt-keeper Wasp larva burrows into the cynipid wasp larva, somehow manipulating it to fast forward its development.
This results in early pupation of the host into an adult wasp. Now, rather than chewing an exit hole and emerging from the gall as the cynipid wasp normally would, its unwelcome inhabitant forces it to chew a hole too small for it to squeeze through.
The cynipid wasp’s head becomes stuck in the hole, where it remains while it is eaten alive by the Crypt-keeper Wasp larva. Upon its own pupation the following spring, this body usurper gnaws through the host wasp’s head/plug, escaping to freedom.
Galls rarely cause enough damage to seriously harm a plant or a tree, especially in a forest setting. Trees planted in a yard can be susceptible to hosting more galls than is typical in a natural setting.
Please keep in mind that though the galls may be unsightly to you, they are vital to ecosystems, providing food and shelter for numerous other species. Attempting to remove galls from a tree can cause harm by exposing it to infection.
Likewise, trying to spray them with insecticides will have little effect on the galler itself but will instead deter the galler’s many natural predators from keeping its population in check.
To learn more about galls, join CPD staff as it welcomes gall expert Tim Frey, who will be leading a gall-centric hike through the prairie and along the woodland edge of Unger Park on Saturday, Sept. 10 at 2 p.m. The scientific study of galls is known as cecidology, so it seems Tim can be called a cecidologist!
Amazing Galls
Saturday, Sept. 10 at 2 p.m. Unger Park, 1303 Bucyrus-Nevada Rd.
Plant galls come in all shapes, sizes, and colors—you may even have some growing on your trees or flowers! The Crawford Parka District invites you to join gall expert Timothy Frey for a hike through Unger’s prairie and along the woods to search for galls.
We’ll learn about the fascinating life cycles of the insects and other organisms that cause them to form as well as some basic gall identification. Tim has a PhD in plant pathology from the Ohio State University, where he studied gall-forming nematodes. He is currently a postdoc at OSU in Wooster, researching the microbes associated with soil and hydroponic production systems.
Galls are his passion, and he travels around the state documenting their presence and abundance. Tim is also an administrator for a great new gall resource, gallformers.org, where he and his colleagues are working to compile a comprehensive database and identification tool for gall-forming organisms in the United States and Canada.
Unger Park is located just west of Bucyrus on Bucyrus-Nevada Road. For more information on programs offered by the Crawford Park District call 419-683-9000, visit our web site at www.crawfordpd.org or follow us on Facebook.
