Galls on California Oaks

I was taking a walk with Joe the dog today in Lime Ridge Open Space, in a specific area where dogs are allowed (most of Lime Ridge is off limits to dogs), when I came across a young oak tree whose every leaf was completely covered in galls.

It was amazing to me that the tree could support this amount of gall growth, and still be healthy and vibrant, and it made me realize that I haven't written much about galls. We have a valley oak (Quercus lobata) next to our driveway, and it has a lot of galls, and only one person on the Urban Farm Tour asked me about it, which is a shame, because I love to tell people about galls. Especially kids, who think they are really cool.

Galls are home to cynipids, or gall wasps, a microscopic non-stinging wasp that can be quite beneficial. (Gall wasps were the particular branch of study of one Alfred Kinsey, before he became a famous sex researcher.) There are a few other insects who make galls, but the vast majority we see in California are made by cynipids. The wasp burrows in to the tree or leaf, or lays an egg; the tree responds by growing these galls, which in turn become a sort of nursery for the baby wasps.

Galls can be quite beautiful, as evidenced by the photo above and by professional photographers, but most are rather mundane, like these:

Some look like mini Hershey kisses!

The area we were walking in today was quite dry and barren, and mostly boring to look at, which is why my eye was immediately drawn to the red leaves on the young oak tree. However, the fennel was blooming, which provided the honeybees some forage, and me some nice anise-scented breaths.

Hiking this time of year really brings home one of the reasons why California is called the Golden State; the hills are truly golden and from far away are quite pretty; but up close all you see is DRY.