Never underestimate the important of preserving the quality of rare books.

A library customer has discovered this the hard way - he faces a $12,000 fine after a number of rare volumes of classic literature were found to be infested with bed bugs.

The valued books were part of an inter-library loan system. They have been fumigated and the library in Denver, Colorado, USA, has been quarantined.

The man, who was one of the library's most avid users, has now been both banned and fined said Celeste Jackson, a Denver Public Library spokesperson, reported CBS.

The man was informed after he returned a second batch of books with more bedbugs.

"When we were returning those materials back in to get them off of his card, some of the bugs fell out," said Ms Jackson.

The bugs' droppings stained the book pages black.

To counter the problem, the library has had to destroy 31 books worth an estimated $12,000.

The customer who returned them has been fined the $12,000.

Bedbugs are notoriously difficult to kill and live in cracks and crevices.

The library believes it has taken care of the bedbug problem and that it is once again safe to borrow books - but has asked that customers do not return books if they are suspected to have a bedbug problem.

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