Have you ever been walking through the woods and found spherical objects that appear to be made out of leaves? While I was doing some work in Charles Ilsley Park, I found one of these intriguing objects. I have seen these in various places for almost my entire life, but never thought to ask what they were. They are commonly referred to as “oak apples” and they are actually a kind of gall made by a kind of wasp! These wasps are just one of the many insects that oaks support: in Michigan alone over 500 insect species rely on oaks!

A gall is the name for an abnormal growth on a plant, frequently caused by an insect to protect their developing young. In fact there are over 700 different kinds of gall-producing wasps all over the world! The wasp lays an egg which then causes the oak tree to start forming the gall around the egg while it matures. A gall is then formed on the tree in order to protect the larvae of the wasp while it is growing.

The gall serves as both a protective barrier against things that would eat the larva as well as a food source as the tree continues to provide nutrients to the gall. While this may seem harmful to the tree, in reality galls formed on the leaves have little to no negative impact on the health of the tree. However, galls that form on twigs have the potential to effect the health of the oak if too many of them are formed on one tree.

At first glance, an oak gall may be seen as nothing more than a byproduct of an insect’s life cycle. However, these galls have a surprising amount of history behind them! The main thing that I found interesting was the fact that they were used to make ink for hundreds of years before more modern ink-making processes. The galls were used as a source of tannins to mix with iron sulfate, which formed the colored part of the ink. These were then mixed in water with a binder such as gum arabic to ensure the ink was able to be written with.

I thought that this was very interesting because I had not realized how far back the history of humans using these galls went. It makes me wonder about how the first people to use these galls probably had some of the same thoughts that I had when I first looked at them. I always enjoy it when I am able to connect two of my interests. In this case I think that it was an awesome opportunity for me to connect my interest in the natural world with my interest in history.

Sources

Oak “Apples” and the Gall-Making Process from Joe Boggs

Iron Gall Ink Mariemayfly on traveling scriptorium