Oak Apple Gall

While hiking (sweating!) along a forested walking trail near my home over the weekend, I came across several types of oak apple wasp galls on their namesake hosts.  These unusual plant growths can range in size at maturity from 1/2 - 2" in diameter and are named for their resemblance to apples.  The galls are constructed of leaf tissue that has been hijacked by a gall wasp (Family Cynipidae) to surround a single wasp larva located within a seed-like structure positioned at the center of the gall.  The exact species of gall-wasp that is responsible for producing the oak-apple gall can be...