The reserve provides habitat for all kinds of wasps. This year, despite the drought, must have been a good year for gall wasps because our oak trees are showing a goodish crop of the various round galls we call oak apples.
In the past oak galls were harvested to make ink. The galls were crushed with ferrous sulfate and gum arabic to make a dense, black, fade-resistant ink. This was the standard formulation used in Europe for the fourteen-hundred year period between the 5th and 19th centuries, and the reason so many ancient document are still legible today.
Oak gall ink remained in widespread use well into the 20th century, and is still sold today. Here is a video to show you how to make your own ink.