Oak Galls

Towards the end of summer, my youngest son and I decided to hike a section of a nature reserve located about a 45 minute drive from our house. The Ridgefield National Wildlife Refuge is comprised of 5,200 acres of marshes, grasslands and wooded areas. Only a portion of the park is open to hiking, but there are plenty of opportunities to view the abundant wildlife which thrives in the area.

This trip, however turned out to be quite different than the few other times we had visited the reserve. Due to the unusually warm and dry summer, and in part to the natural seasonal cycle, much of the vast areas of swampland which abuts the Columbia River, were dried up and had become fields of undulating grasses.

This isolated marsh was on of the only one we encountered on our hike.

This isolated marsh was one of the only wet areas we encountered on our hike.

For the most part, the wildlife we remembered from previous visits, had moved on to locations more suited for species that thrive in riparian environments. Knowing that life abounds in most any condition, we set out along a trail which lead into the oak forest, searching for anything of interest. As evidence of the recent lack of rain combined with unusually warm weather, we noticed that even in the protection of heavy shade, some of the sword ferns were having a hard time of it.

Oregon White Oak GallI stopped along the trail, finding something – a spotted sphere about the size of a ping pong ball, was positioned on an oak leaf which had fallen to the ground. I knew what it was immediately, however, up until then, I had only seen photos.

My focus was to get a few good pictures of our find as I related to my son what we had just found. I was completely oblivious to the yellow jackets that were upset by our intrusion into the territory surrounding their nest. Finally as the swarms anger increased, I clued in to their presents. We moved on.

Now that we were aware of them, we were easily able to find more of the spotted orbs, both on the ground and in the trees hanging from the bottom side of leaves.

So what were these strange little spotted spheres? Each ball was a nursery of sorts. A female wasp had injected a single egg into the tissue of a leaf. A growth hormone was deposited along with the egg, which caused the the surrounding leaf cells to mutate Besbicus mirabilis Larvainto a spherical enclosure. After hatching, the larva was hidden away from predators, with all the food it needed to develop and grow. By Autumn the insect matures and chews it’s way out of the gall to begin life on the outside. This is the speckled gall wasp, also know as the Oregon gall wasp (Besbicus mirabilis).

Like most gall producers, the speckled gall wasp does little or no harm to the tree as a result of the galls it creates. Essentially, gall formation involves the introduction of a growth compound into the tissue of a living plant, which alters its cellular development. Galls are most often made by insects or mites, but other organisms also create galls such as fungi, bacteria, viruses and nematodes. Leaf galls are the most common, but galls of different varieties can be found on almost every structure of a plant. There is a wide degree of variations when it comes to the size and shape of galls based on the species of the gall producer, the type of host plant it has chosen and the area of the plant that the gall is established on. In many cases, an expert can tell the species that produces a gall just by looking at the gall itself.

Besides the obvious round gall on this leaf there are also several smaller galls made by another type of organism shown as yellow patches with brown centers.

Besides the obvious round gall on this leaf there are also several smaller galls made by another type of organism shown as yellow patches with brown centers.

Old Growth Oak TreeSeveral branches have been lost from this massive old growth Oregon white oak (Quercus garryana). This tree has most certainly hosted its share of speckled galls over it’s four hundred year tenure at the park.

Maybe on our next visit to the refuge we will again be able to see the great egrets, nutria, sand billed cranes and bull frogs, but the quiet drama which took place within the confines of the Oregon white oak galls was no less significant.

Oregon White Oak Grove

To read about a couple other interesting galls I have encountered, check out these posts: Mites Meet Maple-Crimson Velvet Erineum Galls and Willow Galls.

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9 Responses to Oak Galls

  1. Renee says:

    Excellent info Rick. I remember seeing the the galls in California on our trip. These are much more colorful.

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  2. Marie Keates says:

    We have lots of galls here in southern England but none as pretty as those you found. All ours are boring brown. Even so, they ŵere once used to make ink and Magna Carta is signed with oak fall ink.

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  3. It’s not at all a galling subject.

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  4. gaiainaction says:

    A very interesting blog post, I am eager to learn more about these gals.

    Like

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