Riddle of the Mystery Grape Solved

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.

36 thoughts on “Riddle of the Mystery Grape Solved

  1. I found one of these this morning. It was right there in the trail, didn’t see any others around but it was such a remarkable structure I pocketed it. Your site was the first I found after quite a search that let me ID the thing. thanks!

    • Hi Ed, Glad I could help identify the gall wasp’s oak apple. What search terms did yo use to finally find the answer to your quest? I had to search through countless seed pod images before I found something that looked like the “mystery grape”.

      • I just found one of these in Garrett County, MD. I found your site very quickly by searching “large round bright green seed pod” 😊

  2. What a bizarre coincidence – we had basically the exact same experience as Ed above – we went hiking today, found the oak apple on the trail by itself, were intrigued by it and brought it home to ID – just a few days after Ed. We finally found your site after googling ‘grape like pod’… Thank you so much for solving the mystery!

  3. Went hiking this morning on part of the Finger Lakes Trail near Ithaca, NY. Saw exactly what you had pictured. Typed in seed pod that looks like a grape and up you popped. Thanks for explanation. That riddle solved!

    • Hmmm… a mysterious speckled green grape all the way up in New York. I wonder how widely oak apples are distributed.

  4. Thanks for the id of this thing. I was camping with friends this weekend in central Wisconsin. One of the kids found one on the ground. We looked around and found half a dozen. Only trees right around that spot were oak and pine. I figured I would google ‘spotted grape like seed pod’. I did and saw a picture of one.

  5. Found the same up in northern NJ in Wawayanda State Park in 2013….In all my years of hiking and biking I thought it was quite odd. Seem’s like all of the comment’s have started in 2013…

  6. Walking to day at lunchtime, I saw a tree about 6 feet tall with at least 50 oak marble galls on it. When I first saw it, I thought someone had decorated it for Christmas.

  7. Joining the chorus – I was really stymied by these these, many of which I found on a hike near Boston. Finally got to your answer when I added “round” to “seed pod”. So glad to know, and to find so many others went through the same process.
    Thank you all

  8. I’ve been wondering what these were! I’ve found them before but I never broke them open, I thought they were magic fruit as a kid! My mom found one today after today’s storm and she wanted to know what it was, and this was the only place I could find my answer! Gives me the chills, though, knowing that I was actually carrying around a gall wasp egg! Thanks for the information!

  9. These have been here in Massachusetts for the past two years. I haven’t seen them on the trees yet, but I wondered whether a bug grew in it. We do have numerous oak trees on our street. We have also had winter moth infestations.

  10. A few weeks ago, I found one of these spheres growing on one of my backyard grapevine branches, here in Rhode Island. I thought it was a grapevine seed pod. Been harvesting grapes from these vines for many years now and never have seen this before, Thank you for your posted information. One Question – should I clip that branch off. Will it damage my vine if I just disregard it, Please reply.

  11. My friend found one of these just 2 days ago, near Wilbur Dam, which is fairly close to the Appalachian Trail in Elizabethton, Tennessee. None of my plant books gave any clue what it was. I could see it was not a seed pod but had no idea what it could be. I googled “hollow green flower bud” and your photo popped up. Thank you so much for the great explanation! 🙂

  12. Googled “Grape like pod on tree leaves” Thank you for your fascinating mystery solution. What I found here today in Justin, TX is a large oak apple and on the opposite side of the tree what appears to be a small gall. I’m not sure if the small gall is really just a oak apple that hasn’t grown fully. These both are translucent but they are not spotted just tinted pink. I became curious when I saw this was actually growing like a paracite out of the leaf part not the stem. I have them if youd like a pic.

  13. I found one of these on a trail at a hunting camp in Coe Hill, Ontario. I opened it because I didn’t know what it was and told my husband I just found an alien egg. He told me to get rid of it because it might cause a skin reaction. Thanks for the explanation! I searched for “green and red spotted tree seed.”

  14. This is so ironic. A friend & I were hiking in our local woods in So. Minn. today & found one of these on the trail. We picked it up to look at it & in the process of handling it it cracked open exposing a beautiful yellow sea urchin looking object. Didn’t have a camera to capture that so took it with us only to discover that it turned brown by the time we went home. Tried to goggle trees & their seeds just like you did to no avail. I finally typed in “small green seed pod with brown speckles with sea urchin looking inside”. So excited to find your post!

  15. Found only one at Fair Hill Natural Resources Management Area in northeast Maryland. Never saw one in 50 years! Brought it Home to show the family. Googled “big green round speckled seed pod” and your post came up first. Thanks for solving the mystery. Not even a seed pod. Crazy!

  16. I just noticed oak “grapes” for the first time on the trail I walk every morning next to the Kennebec River in Central Maine. Thanks for your info.

  17. Live in upstate NY in Adirondack Park and found one near our house this afternoon. Found your site fairly quickly after googling “translucent pod from tree”. Neat! Thanks for the info.

  18. We found one too today and found your site rather quickly using “grape like pod oak” as it was found under our oak tree. We are also in the Adirondack park in NY fairly close to VT side. What a find!

  19. This thing is absolutely bizarre! I am absolutely amazed that so many of us have experienced nearly the same circumstances where we stumbled upon this “oak apple” thing. I find it hard to describe how I even feel about this odd example of natures anomaly. Thank you for helping solve this mystery.

  20. Thank you! I was outside today in Uxbridge, MA throwing out some peanuts to the local squirrels when my attention was caught by a weird green “skin.” I saw several open pod-like items before finding one that was intact. I brought it in the house to research it and came across this page. Thank you for the explanation! I immediately tossed the “pod person” back outside. 😀

  21. My husband and I were cutting trees that we had felled around our camp in Clarence, PA boarding the Sproul State Forrest yesterday and found one on a tree branch. Thank you so much for helping us in identifying it!

  22. This is just so funny. I was walking in the woods today and found a brown speckled crispy ball. I search “hollow brown seed” in google and one of your pictures was the third result. Thanks for posting!

  23. I actually have a treeful… And they grow fast, I didn’t notice until this morning but they popped up in just over a week…. Thanks for the foot work!! If I knew how to upload the photos I’d domit

  24. Found some on our tree in the back yard, in Dallas, Texas yesterday. Noticed they were on the lower branches of the tree. Guess I need to get rid of them before they hatch??

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