The galls hung down like baubles on the branches of a Garry Oak tree that I encountered on my walk. I had never seen so many on one tree before, and was entranced by all of the colors, from greenish yellow to beige to burgundy/brown, and sizes from quite small up to one inch (2.5 cm).
Galls dangling from the undersides of Garry Oak leaves
Although more than one type of wasp causes galls on Garry Oaks, I believe these were caused by the Oregon Gall Wasp or Besbicus mirabilis. They inject the Garry Oak leaves with a substance that causes the galls to grow for the purpose of housing and feeding the wasp larvae. When the mature wasp is developed, it chews its way out of the gall and flies away to begin the process again. Apparently, the galls do not seriously harm the tree.
Multi-colored galls caused by a tiny gall wasp
I just had to take some samples to study, so I returned the next day and clipped some small twigs. When I got home, I carefully cut open a gall with a scalpel and found some gossamer webbing inside but I couldn’t see an occupant. I cut open a few more galls…with some trepidation…and finally found one with this little larva inside. I am not sure whether it is a Gall Wasp larva since the galls are a complex ecosystem in themselves and sometimes they house the young of intruders.
Inside the galls is this gossamer webbing. A small larva crawled out, but it may not be a wasp larva.
I took along some galls to sketch and share at an OBA meeting, and below is the result.
A small study of some oak galls attached to the underside of a Garry Oak leaf
This blog is about my journey as a botanical artist--what I am learning, what inspires me and what I am currently drawing or painting. My desire is to continually hone my skills to better express my wonder and gratitude for the beauty of the creation around me in the Pacific Northwest (USA).
Hi Janene,
Thanks so much for sharing this interesting post, the beautiful drawing, and for sharing the branches and galls themselves with us at the August meeting. I really enjoyed drawing them, too, and have always found them sort of magical when I’ve encountered them in the woods.
Janet, it’s great to have you and the other like-minded people to meet with each month. I am glad that you enjoyed the galls as much as I did!
Wow, isn’t that fascinating! I think I would have been equally anxious about slicing one open, not quite knowing what lies within! Galls are so interesting and your sketch is wonderful
Galls are one of those strange yet wonderful things in the natural world, all the more so knowing that something is alive inside! Glad you enjoyed the post.
A beautiful sketch of a wonderful phenomenon in nature. I love these bits about how it is all connected. And I admire your naturalists curiosity to explore and discover more about it.
Well done!
Thanks Deb! I had no idea about the complexity of galls when I started researching them and now have barely scratched the surface. This blog is a good motivator to me to look a little deeper, and it is so rewarding when friends like you enjoy the results along with me!
How could I have lived to this age and never heard of the oak galls? That was fascinating, Janene. I will be looking for them now when I’m in the vicinity of oak trees. Your sketch is lovely, too. I’m in awe of how much detail you got in the leaves.
Vicky, I am so excited for you to see oak galls. You’ll have to stop by sometime and I’ll show you the tree with all of the ‘baubles’ near my house! Thanks for your encouragement.