What’s That? Oak Galls

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This time of year, acorns large and small start to rain down all around MAGC, keeping the squirrels busy and the rest of us on our guard. You may have noticed some other, more unusual objects growing on and falling from our oaks: oak galls, sometimes called oak apples. Their rounded shape and surprisingly light weight makes them immediately appealing to kids, although according to some childhood lore they are poisonous. Not true! They are the tree’s response to specific species of wasps, which lay their eggs in a developing part of the tree, causing the gall to develop around the growing larvae, protecting them and providing a source of food. More intriguing still, the exact process by which the insects prompt the host plants to produce the galls is not fully understood. Oak apples are just one of a huge range of different types of gall that can form on almost any part of the plant, and can even be quite beautiful. In the photo here, you can see how—somehow—a gall has grown around a small stone, an even more unusual example of this interaction between insects and plants.

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