Galls at Stulsaft Park, Redwood City, CA

I don't think I'd ever walked around Stulsaft Park, a decent-sized city park on both sides of the Arroyo Ojo de Agua creek in suburban Redwood City. It has several varieties of oaks growing together along the steep slopes. This time of year, oaks come with galls in various shapes, colors, and textures. Wonderful life!

Rose galls

Diplolepis is a genus of cynipid wasp that induces galls on our native wild roses. I'd never noticed them before this spring. Recently I stumbled across two different species that produce similar spiny galls. The first, D. bicolor, occurs along the stem; I saw it in Armstrong Redwoods State Park. The second, D. polita, grows on the leaf (photo below); these were at Hidden Villa. D. bicolor has the honor of being the cover photo of Ronald Russo's wonderful guide, Plant Galls of the Western United States. Lucky gall!

The crazy reproductive life of gall-inducing wasps

"Cynipid wasps are responsible for the most extreme galls in color and shape. Galls that look like miniature stars, sea urchins, golf balls, cups, saucers, clubs, teardrops, goblets, and bow ties are among the fascinating shapes that stir the imagination.... 

"Cynipids typically exhibit an ALTERNATION OF GENERATIONS, called HETEROGONY, with a spring sexual generation emerging from a different gall (often from a different plant organ) than the summer-fall generation of unisexual females (agamic generation). The latter females overwinter in diapause as prepupae (usually in the galls) and then pupate and emerge in spring, timed in harmony with the development of the preferred plant organs. Eggs produced and deposited by these females result in larvae and galls of the spring sexual generation. This alternation of generations is rather rare in the animal kingdom but also known in aphids and rotifers. This interesting alternation of reproductive modes confused early entomologists, as the alternating generations of the same species induced galls with different morphologies. This led researchers to believe the different galls belonged to separate species or even other genera."

Ronald A. Russo, Plant Galls of the Western United States, p. 48

Little things

I took this blurry close-up of a valley oak leaf with my phone the other day in Arastradero Preserve... the little red pimple- or volcano-shaped galls caught my eye, although they knocked off so easily I wonder if they were not some kind of scale insect. At any rate, I missed the handsome jumping spider entirely, until I cropped the picture...

Gall

On my black oak. One of many varieties found in our great state.

California’s 22 species of oaks... are known to support over 200 species of cynipid gall wasps, more recorded species than North Africa, Europe, and Asia combined.