In modern Europe the common furniture beetle and the Mediterranean furniture Beetle overlap in terms of their locations, but this didn't used to be the case. In previous centuries the beetles kept to very distinct and separate regions... and the reason we know this is because of woodcut books. In the 1400s Europe started using woodcuts - carved wooden blocks - to produce images in a form of early (for Europe) printing.
The problem then was that the beetles would leave their larvae in the type of wood used, and after the blocks had been created the beetles would emerge and leave small holes, which can be seen as white dots in printed books. Penn State biologist Blair Hedges has surveyed nearly five hundred books made with woodcuts from 1462 to 1899, and traced the former separation of the species thanks to the distinctive difference in hole size and track mark. Without the books, this detail of biological history would have been unknown. For more information see MSNBC.