There are many species of parasitic Cybnipid Wasps that induce many different kinds of galls on many species of oak trees. A female wasp deposited her eggs into these stems when they were new, green and growing. After hatching, the larvae secrete chemicals which mimic growth hormones that “trick” the tree into forming a protective gall around the larvae, providing shelter and food. The holes we see are the old exits left by emerging adults
