A bookworm / beetle grub found inside a paperback book, showing some of the damage it has wrought
Bookworm is a popular generalization for any insect that supposedly bores through books.
Actual book-borers are uncommon. Two moths, the common clothes moth and the brown house moth, will attack cloth bindings.
Leather-bound books attract various beetles, such as the larder beetle and the larva of the black carpet beetle and Stegobium paniceum.
Larval death watch beetles and common furniture beetles will tunnel through wood and paper (if it is nearby the wood).
A major book-feeding insect is the book or paper louse (also known as booklouse or paperlouse). These are tiny (under 1 mm), soft-bodied wingless Psocopterans (usually Trogium pulsatorium), which actually feed on microscopic and other organic matter found in ill-maintained works (e.g., cool, damp, dark, and undisturbed areas of archives, libraries, and museums), although they will also attack bindings and other book parts. The booklouse is not a true .
By the twentieth century, modern bookbinding materials thwarted much of the damage done to books by various types of book-boring insects.