I was walking under this giant live oak that is in my front yard and I noticed all of these perfectly round, brown balls on the backs of the leaves. I mean there were a lot! I had no idea what they were, but knew they didn’t really belong so I did some research and discovered that they were created by a type of wasp and that the wasp actually triggered the tree to create this “cocoon” for the wasps offspring.
There are many species of gall wasps found in Florida and throughout North America. They belong to the family Cynipidae. The wasps that form galls are quite small, 2-8mm long and they don’t really look too much like the large ones that commonly cause fear and commotion.
The perfectly round, brown ball-like gall is one type that can be formed, but different wasps create different galls and they can be found on different parts of the host tree like on the roots, twigs, buds, flowers and leaves. Where the wasp chooses to form the gall depends on what part of the tree is actively growing.
The female wasp is the one that creates theses galls. When it is time for her to lay her eggs, she finds an oak tree with actively growing tissue and deposits an egg onto the surface. Once this is done, there is some kind of chemical reaction that causes the tree to form a gall around the egg. This gall is formed to protect the egg inside and then it will also create a safe “nursery” for the wasp larva as it matures.
Although these galls can become unsightly, I don’t think they cause too much damage to the trees. I have an oak tree that is loaded with them, but the tree seems to be healthy and strong. These galls also provide food for wildlife. Birds will break into them and eat the larva or egg that is inside and squirrels will eat whole galls.
I am not sure if there is any way to control wasp galls, but I don’t think that it is necessary either. These wasps do not cause a threat to people or pets and I don’t think the trees are really damaged either.
Deyrup, Mark. Florida’s Fabulous Insects. World Publications. 2000. Pg. 149
National Audubon Society Field Guide To North American Insects And Spiders. Alfred A. Knopf, Inc. Chanticleer Press, Inc. 1980. Pg. 813