We all know forests harbor diverse ecosystems...

As such, even in densely populated areas, trees of all shapes and sizes thrive. I only live about ten minutes outside of the city, and I have towering conifers on my property, grand deciduous trees, and a plethora of birches. Like many yards, I also have plenty of oak trees.

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In fact, let's take a minute to marvel at the majestic oak... Of all the trees in your yard, the oak is practically a small habitat all by itself. So many creatures of all varieties depend on the mighty oak to provide it shelter, or food, or sometimes even both. We've all seen the giant squirrel nests up in the top, presumably chock full of acorns for winter.

There's one oak dweller though, that's enough to make you a little nauseous.

Ever seen these little green "blisters" on an oak tree? Or maybe you've found a brownish pod version of this, lying on the ground somewhere and wondered what they were. These are called "oak apples" or oak "gall". Most people assume it's some kind of little naturally occurring infection or something. Noooope. It's way more gross than that.

Oak apple or oak gall on two fallen dry leaves found in a forest in springtime isolated on white background.
Getty Images/iStockphoto

These little balls are actually the home, so to speak, for a gall wasp. Adult gall wasps will inject a chemical into the leaf buds as they're forming, and these little green balls form in that spot, providing us with these funky-looking mini-apples. But you may not want to think about eating one...

There's a whole life form growing in there.

When gall wasps are in the larva stage, they grow inside the balls until they mature. While inside, they feed off the nourishment provided by the ball and tree. Eventually, a full-grown gall wasp will emerge from the ball and do its thing. Eventually, those adults will do the same thing, and the process continues.

READ MORE: That Ball of Leaves in Your Tree Isn't a Bird's Nest

Cynips quercusfolii known as gall wasp, round ball gall underside of common oak leaf Quercus robur. Inside is bug larva. Autumn day.
Getty Images/iStockphoto

Unless of course, a competing kind of wasp manages to penetrate the shell of the oak gall and lays their own eggs inside. So even inside the cozy home of the oak gall, the larval gall wasps are not safe. Mother Nature can be such a cruel jerk at times.

Opened Oak Gall
UWyoExtension via YouTube

But still, knowing that those little balls on the tree actually contain some grody baby wasp isn't really something that sounds like good news either.

In case you were looking to be a bit more grossed out by bugs...

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