https://www.naturespot.org.uk/species/cherry-gall-wasp Cynipidae · gumbavapsvės Oak apple gall (cecidia) · ąžuolo rašalinis riešutėlis
https://en.wikipedia.org/wiki/Oak_apple: Oak galls have been used in the production of ink since at least the time of the Roman Empire. From the Middle Ages to the early twentieth century, iron gall ink was the main medium used for writing in the Western world. Gall nuts are a source of tannin in the production of iron gall ink. The reaction between the tannins from and the iron (iron sulfate) produces a complex that gives the iron gall its color.