Galls: Amazingly Diverse and Fascinating Plant Growths

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Show notes:

Have you ever found a leaf with weird little balls or spiky things attached to it? Or found a plant with a weird growth on its stem or a dense clump of leaves growing out of an odd place? Chances are those were galls.

Going into this conversation, I knew a little bit about galls, but not much. However, what I knew was pretty interesting. So I wanted to learn more, and I thought you might be interested in learning more about them too. My mind was almost instantly blown. Galls are so much more diverse, interesting, and amazing than I ever dreamed of.

Louis Nastasi joined me for this conversation. Louis is a PhD candidate at Penn State’s Frost Entomological Museum which is Penn State’s research collection of insects and other arthropods. His research is looking at gall wasps in prairie plants, particularly Silphiums, of the Midwest.

At its most basic level, a gall is a piece of plant tissue that has been modified by the activity of another organism. However, in reality, galls are so much more than that implies. They can be formed by a variety of different organisms, although most of the ones we think about and encounter are formed by different types of insects. They can also be found in a variety of different places on the plant, including hidden inside the stem in such a way that you would never know it was there unless you cut the stem open.

Louis and my conversation touches on all kinds of topics related to galls. We start out talking a little about what galls are and the types of organisms that can form them, then focus more on insect-induced galls. From there our conversation covers topics like why insects might choose to form a gall in this plant over that plant, the importance of galls and the ecosystem, and how little we actually know about galls.

This was a really fun and educational conversation. I learned so much and am completely intrigued. I could have kept discussing and learning more about galls for much longer because they are so much more complex and interesting than I realized. I hope you find the conversation as interesting and educational as I did. I also encourage you to check out the resources that Louis shared with us.


Episode image:

  • A gall on a leaf.
  • Photo credit: Andy Deans, all rights reserved

Backyard Ecology: Exploring Nature in Your Backyard
Nature isn’t just “out there.” It’s all around us, including right outside our doors. Hi, my name is Shannon Trimboli, and I am the host of Backyard Ecology. I live in southcentral Kentucky and am a wildlife biologist, educator, author, beekeeper, and owner of a nursery specializing in plants for pollinators and wildlife conservation. I invite you to join me as we ignite our curiosity and natural wonder, explore our yards and communities, and improve our local pollinator and wildlife habitat. Learn more or subscribe to my email list at

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