Insects galls on oak have great historical significance as a source of inks used to write documents. These include the Dead Sea Scrolls, many copies of The Bible made prior to the Gutenberg press, drafts of the US Constitution, the notebooks of Leonardo da Vinci, musical scores by Bach and artwork by Rembrandt and Van Gogh.
Oak gall inks do not smudge like the carbon inks (the very first inks). They hold their color and do not fade rapidly like some of the modern inks in use. However, some of the inks can have a corrosive effect on paper and papyrus over time depending on the recipe that was used. This complicates preservation of some documents.
The galls produced by the oak gall wasp (Family: Cynipidae) are ground to a powder or boiled and the gallic acid extracted. The gallic acid is mixed with iron sulfate, gum and water to produce the ink. For those that would like to try this at home, Cyntia Karnes of the US Library of Congress, maintains a website with recipes and cool information about gall inks. This site has a lot of historical information and photos of documents made with insect ink.