Natural History Wanderings

What are those funny looking bumps on that oak tree?

As the flower season and foliage season end, I start to pay attention to the more subtle (at least to me) aspects of nature such as lichens, mushrooms, mosses and galls.  Galls are the interesting looking tumor-like casings that we find on plants, often oak trees.  Galls are formed as a response by the plant to insect larvae releasing compounds. These compounds  redirect the plant tissue  to growth to form a protective shell around the larvae.

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Most galls are the caused by insects.  Most galls are the result of midges and wasps but can also be caused by other insects, mistletoe, some bacteria, fungi and mites.  Approximately 13,000 species have developed the ability to interact with host plants and create galls.

To learn more about galls read the article in Natural History Magazine by Ron Russo Confessions of a Gall Hunter

I  recommend Ron Russo’s Field Guide to Plant Galls of California and Other Western States as a helpful resource for learning more and identifying galls.  He is also an interesting and informative speaker on the subject.

If you are interested in further studies the Jepson Herbarium is offering the following workshop on September 18, 2011
Insect-induced Plant Galls of California Instructors  Diane M. Erwin, Joyce Gross, and Kathy Schick
UC Berkeley

Related Articles

• Oak galls won’t cause any damage to trees (video): Ask OSU Extension (cleveland.com)
• A Girl with “Gall” Wins Young Naturalist Award (amnh.org)