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Are those kisses on my oak leaves??
Have you noticed brightly colored, strangely shaped things stuck to the leaves and other parts of your oak tree? They often look like red Hershey kisses, pink fleshy hands or multi-colored disks. These weird growths are oak galls!
These bizarre structures are created when the cells of your tree respond to the growth of cynipid wasp larvae within them. These wasps are not the kind that sting humans or animals. In fact, the wasps are so tiny you have probably never even noticed them. They also do not hurt your tree and do not need to be “treated” or removed. They are a natural part of our oak woodland ecosystems. There are over 150 different species of cynipid wasps that specialize on oak trees. You can look at more photos of oak galls and get more information from these websites and books:
Field Guide to Plant Galls of California and Other Western States by Ron Russo, University of California Press (2007).