Sentence:  Once inside, they begin to mine; there may be apparently nothing wrong outside, but when you open the book you find a hollow filled with insects, which have eaten almost all the letterpress, up to the margins. By keeping the shelves away from the walls and giving a little attention to wormy volumes, the Library may be easily freed from this kind of <WSD>Bibliophage</WSD>. 
Meaning of the word marked with <WSD> tags:  A creature that consumes books' physical contents.