Posted April 28, 2023
Galls are some of the most fantastic animal-created structures in nature. That’s just my opinion.
They may look abnormal, unnerving, or like they don’t belong. But, understanding more about galls opens up an entire dynamic at play.
Plants don’t produce these structures on their own.
Instead, galls are formed when an insect or mite “hijacks” the meristematic tissue of a plant. Meristematic tissue contains undifferentiated cells which can become all types of things a plant might need. You can think of this tissue like Freshman in high school. They’re quickly growing, but they don’t really know what they are going to do, just yet.
Through processes that aren’t fully understood, the gall former causes this meristematic tissue to grow into something it wants: Tissue that is both more protective and more nutritious than the surrounding parts of the plant. And, voila! You have a gall.
But, let me say that again: gall formers change the DNA of plants to suit their own purposes. Wow!
It’s been said that anything humans invent, nature has done long before. I don’t know the validity of that statement. But, I can say that invertebrates have been making genetically modified foods (“GMO”) for about 385 million years (Labandeira 2021).
If that isn’t cool enough, some believe that all fleshy fruits originated from galls produced in the reproductive tissues of plants (Pirozynski, 1991). You might thank bees for 1 in 3 bites of food (Klein et al. 2006), but you can thank wasps for 100% of the fleshy fruits you have.
And, fortunately, most galls shouldn’t cause much damage to the plant. Galls laid on or near the reproductive parts of the plant would, of course, interfere with reproduction. But, if there are many individuals of that plant, the resultant damage shouldn’t greatly impact the overall plant community.
Galls can be formed by many organisms. Wasps, mites, and flies make up most gall producing organisms. Most of the galls you find will be formed by one of these three. But, there are other gall formers, such as aphids, beetles, and moths that exist.
The gall formers and their structures support a bevy of life. The animals themselves may be food for birds. They may serve as hosts for parasites. We even have at least one butterfly here that consumes the nutritious gall tissue: the caterpillar of the cherry gall azure.
The protection that galls afford allows some animals, such as some bees, to use abandoned galls as homes. Other animals may not even wait for the gall former to leave. They opt to live alongside them as inquilines. These are organisms that exploit the space of another.
Looking at galls as natural and normal will open a whole world of diversity right under your nose. You’ll find many different types of galls in and around your neighborhood.
For more on galls, check out Tracks & Sign of Insects and other invertebrates by Charley Eisman and Noah Charney.
Written by Blake Dinius, Entomologist Extension Educator for the Plymouth County Extension