What is an Oak Apple?

A collection of oak apple galls.

A collection of oak apple galls.

Very few things in the woods interest me as much as the oak apple. You may be thinking that oak trees produce acorns, not apples. That is true. But oak apples do exist and I for one love to find them. A colleague said that children would love the oak apple magic trick. On a recent hike, it was evident that adults love the magic trick, too.

What is an oak apple? An oak apple is not a fruit. It’s actually a gall from the oak apple gall wasp (Amphibolips confluent). This gall is the size of a golf ball and can be two inches wide. It has a papery feel and is initially leaf-green. Eventually it turns brown and dry. In this case, the gall is actually a mutated leaf.

What is a gall? Plant galls are abnormal outgrowths of plant tissues. They can be caused by various parasites, from fungi and bacteria to insects and mites.

This is NOT where you'll find the oak apple gall...but it is a silly way to collect them—or pretend you're roasting marshmallows! Photo by Martha Fox.

This is NOT where you’ll find the oak apple gall, but it is a silly way to collect them—or pretend you’re roasting marshmallows! Photo by Martha Fox.

How does the gall form? The gall forms when the wingless adult female lays eggs into a newly-forming oak leaf. As the egg hatches and larvae grows, a chemical reaction causes the leaf gall to grow with it.

What is the lifecycle? Adult wasps hatch from the galls in June or July. After mating, female wasp drop to the ground and burrow into the soil. Then they inject the oak’s roots with eggs. Once the eggs hatch, the larvae eat the roots for over a year. After resting in the pupa stage, the wingless adult females crawl out of the soil and up the trunk until they find a newly forming leaf. Next, the wasp injects an egg into the leaf. Each apple gall has only one larvae inside. When larvae is full grown, it pupates into an adult. The adult will bore its way out of the gall, find a mate, and start the whole cycle over again.

Where can I find an oak apple? You may find an oak apple gall anywhere that oak trees grow. June through August is the best time and most are found on the forest floor. If the oak tree is small enough to reach the branches, you may find one still attached to the leaf. Black, scarlet, and red oaks are the preferred species.

Does the gall hurt the tree? No. However, a heavy infestation may cause the tree to lose leaves prematurely.

Shane Gibson demostrates his oak apple gall "magic trick"—make it hover above you! Photo by Martha Fox.

Shane Gibson demonstrates his oak apple gall “magic trick”—make it hover above you! Photo by Martha Fox.

Ok, so what is this oak apple magic trick? The magic of the gall is its ability to hover above one’s lips. The may not truly be a magic trick, but it is amusing. While tilting your head back or lying flat on the ground, hold the gall above your lips while gently blowing. Once a steady stream of air is present, let go of the gall and watch the magic. As I mentioned, it’s pretty amusing to people of all ages!

If the heat of summer keeps you from the woods, decomposition will likely get the oak apples before you do. Finding an oak apple is as magical for me as hearing a migrating warbler is for others. Each experience in nature reminds me of words written by Aldo Leopold, “No matter how intently one studies the hundred little dramas of the woods and meadows, one can never learn all the salient facts about any one of them.”

Enjoy Yourself. Enjoy Nature.

Shane Gibson
Environmental Education Director