If I had not chosen to study flower-visiting insects in graduate school I almost certainly would have become a cecidologist, one who studies plant galls. Invaders such as fungi, viruses, bacteria, mites, and even mistletoe cause these abnormal and often strange-looking growths on plants, but most galls are induced by insects, our principal focus here. The word “gall” comes from the Latin galla, meaning oak apple, a conspicuously large gall caused by a tiny and rarely noticed wasp in the Cynipidae family. Oak apples are a common sight on valley oak trees throughout the West. Oaks in California’s Central Valley may also host jumping galls induced by another species of cynipid wasp. About the size of a flea, these tiny galls detach from the tree and drop to the ground by the thousands where the larva encased in each gall cause it to bounce about in the manner of Mexican jumping beans.
Spiny bud gall Illustration: Craig Latker
Hundreds of other species of cynipid wasps induce galls and, like other gall-inducing insects, are generally host specific, seeking out particular species of plants. When cynipid wasp...
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