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Photo: Diane Edwardson, August 4, 2014. A huge, tennis ball-sized gall (a woody growth containing wasp larvae) appeared, seeming overnight, on the Blue Elderberry Tree in our backyard. The next day, it was gone. (Click on photo to enlarge.)
Galls are formed by trees in reaction to a gall wasp laying eggs in the branch. The larvae grow in the gall (which does not harm the tree) until they break out of the gall as mature adult wasps. According to Bug Guide, there are more than 750 species of gall wasps in North America. In this area, you usually find galls on Coast Live Oaks. I'd never seen a gall on Blue Elderberry.
Photo: Diane Edwardson, August 4, 2014. Since this gall was so large, I noticed it immediately. The next day, it was completely missing. I suspect the marauding raccoons found an good source of protein in the larvae. (Raccoons stripped the fruit trees in our yard this summer.)
