I knew they weren’t actually marbles, but they fascinated me none-the-less. Scattered upon the ground under a spreading Red Oak tree were dozens of them – small globes nearly perfect in their roundness, They reminded me of those glazed clay marbles of old with their pinkish-maroon coloration and speckled appearance. All had some heft to them and this also lent itself to the marble analogy. Unfortunately, they were slightly too large to use on a Chinese Checker board and not quite heavy enough to engage a glass marbled foe in a round of parking lot Ringer.
That these were some type of Oak Apple Gall I was certain (at least as far as certainty can go when talking to oneself). Galls are structures created when an insect lays its egg in a plant stem or leaf and causes the tissues to swell up. Specific structures form on specific plants due to specific insects. With all that specificity going on there are thousands of gall-making insects that can be identified based on gall shape and host plant alone. We hardly ever see the actual insects because they are minute – to say the least. Oaks are especially prone to galls and Oak Apples are caused by eensy weensy wasps.
Given this complicated background it is not sufficient to simply identify an oak gall as an Apple Gall and get away with it. It is morally o.k. to do so (lightening will not strike you down, for instance) but slightly lazy. Unfortunately for you, I was not feeling lazy when I set about to write this blog. You see, there are some 50 species of tiny oak apple gall-producing wasps in North America. These galls are divided up into spongy and hollow types. Lest you are getting a bit uncomfortable here please hang on – I am not that un-lazy as to go through the entire process.
Suffice it to say that Hollow Oak Galls look like the solid ones (see here) but the proof is in the holding. They can be speckled and luminous, just like the solid ones but slightly more oblong vs. round, but have no weight (really?). Hollow galls are mostly air (really, Gerry?) so they…O.K., I’ll stop. You get the point, But, I insist on showing you the incredible innards of a hollow oak gall (see here) just because I can. The grub lives in the small chamber at the center of all those tendrils (see here).
The issue here is really about those original solid galls which I held in my palm. If I were continuing on the hollow oak gall thread I’d have to find out the exact type of the pictured examples and I’m not going to do that. No, the question is the exact identity of these solid marble galls.
The real surprise came in cutting one of these things open to reveal the deep liver color of the insides. Beads of “blood” actually dripped out of the cut as if slicing into a fresh Dik-dik liver. I’ve never actually cut into, leave alone seen, a real Dik-dik liver but it sounds so much more fascinating than saying a deer liver. Dik-diks are tiny African antelopes so they would have, presumably, tiny livers closer in size to a solid oak gall right? I’m just trying to be visual here.
The juice content of these galls was so heavy that it prompted me to make a few gall prints on the back side of a receipt that I had in my pocket. The reddish color remained intact on the paper after it dried– a fact that should not be surprising when you consider that oak galls have long been a source of ink. The prints even revealed the central hollow chamber where the insect itself resides (see below).
A pint-sized grub came out of that center. There was no real way to reverse this step once completed. I suppose it possible, even if impractical; to tape the two halves together but in this case the grub was also cut in half. Let’s just say that if this had been a Dik-dik inside that gall it would have been rendered into a singular Dik. A dead Dik (at which point you should be saying Ha as opposed to Ha Ha).
Because the tiny wasp larva unwillingly sacrificed itself for the sake of education, he and I were committed to completing his story even if it hurts (more him than me). After some time I arrived at the correct identity and am able to tell you that this type of solid gall is called an Oak Acorn Plum Gall. Got that? The scientific name of the actual wasplet is about a mile long and it would hurt me to have to type it out. You can Google it if you really want to know.
Apart from the Dik-dik like nature of the galls they are unique in that they develop off of the acorn caps. Most, if not all, of the oak apples form out of the leaves. The galls are about the size of the nut itself before they fall off.
The larva inside the other Plum Galls layered over the ground will eventually pupate and emerge as micro wasps about the size of the “o” on this page. They will generate a whole new crop of marbles next year and I will only cut one open if asked (you’ll need to ask twice). The question is whether you will Google that scientific wasp name or “Dik-dik liver” first.