I’ve finally solved the riddle of the Mystery Grape. The mystery started when I found a spherical translucent speckled green grape-like “fruit” lying in the middle of the Appalachian Trail in Pennsylvania. Native Pennsylvania grapes are not green and there weren’t any visible grapevines in the area. So what did I find?
I literally delved deeper into the mystery by ripping open the green sphere to reveal an even more mysterious center mass resembling a white sea urchin. The central mass had tendrils which reached out through hollow space and clung to the bright green soft outer shell. It looked alien, like something from a science fiction movie that, if left unchecked, would grow into a pod-person.
So I researched seed pods and seeds, sorting through a variety of identification charts only to come up short. Nothing was green and speckled with an urchin-like center. I browsed through countless pictures of seed pods until I found one that looked very similar to what I had held in my hand. But it wasn’t a seed pod.
It wasn’t a scuppernong, it wasn’t a mayapple, it wasn’t a gooseberry; in fact it wasn’t a fruit, vegetable or seed of any kind. The only guess I made that was even close was that of “alien pod person”. The speckled green mystery grape is actually a plant/animal hybrid (planimal?) called… a “gall”.
A gall is an abnormal outgrowth of plant tissue caused by parasites. Ewwwww. This particular type of gall is called an Oak Apple and it’s caused by a Gall Wasp. Neato! Basically a tiny little gall wasp lays an egg in the stem of an oak leaf and then the tree has a reaction that causes the leaf to grow a tumor-like structure which encapsulates and nourishes the wasp egg. Within the center of the urchin-like mass the egg grows into a larvae, metamorphosizes into an adult gall wasp and then the adult wasp eats its way out of the protective skin of the gall. It’s like a “chestburster” from the movie Alien but for oak trees.
While I may have identified the “mystery grape”, the mystery of the Oak Apple and the Gall Wasp still continues. Biologists have yet to identify the means by which the gall is formed, current theories include chemical, mechanical and viral triggers. In fact, the Gall Wasp is of such a peculiar nature that renowned entomologist and sexologist Dr. Alfred Kinsey spent the first half of his research career focusing on Cynipidae (gall wasps). It is also believed that the peculiar reproductive cycle of the gall wasp may have influenced Kinsey’s controversial perspective regarding human sexuality.
While there are both male and female gall wasps, some females can reproduce asexually, this is called parthenogenesis. The single wasp that emerges from a large Oak Apple will be parthenogenetic (i.e. agamic, asexual) and will lay eggs somewhere other than a leaf stem such as a bud. The egg in the bud will generally develop into a little gall that is much smaller and less noticeable than an Oak Apple. When this little gall fully develops, a male or female wasp will exit and seek a mate. Once fertilized, the sexual female will seek out an oak leaf stem and implant an egg which in turn develops into a large Oak Apple. This is the reproductive cycle for the majority of Gall Wasp types.
As noted above, not all galls created by Gall Wasps are Oak Apples. In fact nearly every different type of Gall Wasp creates a uniquely identifiable gall. An accurate description of the gall and the plant on which it is found, is enough information to identify nearly any species of Gall Wasp, but… that doesn’t mean you can tell what will emerge from a particular type of gall.
The structure and composition of a gall is amenable to any number of parasitic or inquiline species. A parasite will take over the gall to the detriment of the Gall Wasp while an inquiline will live along with the Gall Wasp without harming it. Galls are almost equally likely to give rise to the native gall wasp, its parasite or its inquiline. The often succulent and nourishing nature of galls also attracts predators like woodpeckers which savor the grubs found within. Another gall predator is man.
From the 12th century to the 19th century people would collect Oak Apple galls as well as a few other types of tree galls to create “iron gall ink” which was Europe’s primary ink source for centuries. Iron gall ink was preferred because it adhered very well to parchment and vellum which were the predominant writing materials of the time. Iron gall ink fell out of favor due to its chemical incompatibility with paper products and the Oak Apple’s prominence has been fading ever since. Maybe that is why so many people were unable to solve the riddle of the Mystery Grape.