What is a bookworm? A bookworm is any number of insects, or the larvae of insects, that eat books. They are not actually worms.
Why would an insect eat a book? What food is there in a book? Some insects don’t actually eat the books, but fungi and mold that grow on the pages of the book. They may inadvertently eat some of the book as well, while they are eating the fungi. If the books are kept in damp or humid air, mold can grow very easily and insects thrive on it. The insects that eat the book itself are eating the cellulose in the book. We cannot digest cellulose, which is why it is important for us to eat it. It is a source of fiber and it helps us pass food through our digestive system. Most insects can’t digest cellulose either, but there are some and those are the ones that feed on books. They can eat the pages to get at the cellulose. There are some insects that feed on the glue that is used to bind the books because that has a lot of starch in it. Some insects will eat the leather or the material binding of books. Some insects will burrow into books to lay eggs. There are also rodents that will use the book pages for nesting, or who will just chew the books.
There are many insects that eat books. Here are six of the most common. Silverfish. They are about 2 cm long and they have silver scales, which make them look like a fish, hence their name. Silverfish are one of the few types of insects that can digest cellulose. Most insects and animals can’t because it is very tough and very difficult to digest. Quite often, you would need to put in more energy to digest it than you would get out of the cellulose itself. There are far easier sources of energy. Silverfish have evolved a way to digest cellulose and they feed on it. They will eat anything, including carpet, hair, and paint, but they also eat books. They eat the cover, the pages, and the glue.
Cockroaches and termites are big eaters of books, although they eat anything and only damage books if they happen to be there. Termites can eat wood as well and they usually destroy the shelves as well as the books. Termites might tunnel through the books and the shelves, while the larvae of cockroaches will stain the books.
Book lice are tiny wingless insects that infest books. They are very common, but they are not there to eat the book. They are one of those species that live on the mold and the fungi that grows on the pages of old books. If you keep your books dry and temperature controlled, book lice probably won’t be a problem.
There are some beetles that eat the edge of book pages and the leather covers. The cigarette beetle can lay its eggs on a book and they burrow tunnels through the pages. They burrow through lots of things, not just books, but if they are laid on books, they will make tunnels. This could be where the word bookworm comes from because the tunnels look like they were made by a worm.
Rodents will also eat books. Rats and mice can chew through books. They can’t digest the cellulose, but they can get the starch out of the sugar. However, there is more chance that they chew up the books looking for other food or to use the paper to make a nest. Rats also have to constantly chew on things to wear their teeth down. Our teeth don’t grow after our adult teeth come in, but rats teeth grow continuously throughout their lives. If they don’t gnaw on things to wear their teeth down, they will get too long to be useful.
The only way to protect old books from all of these things is to keep them in a sealed, temperature and humidity controlled room. Pesticides can kill all of the insects, but they will damage the books as well.
Incidentally, bookworm also applies to a person. It means someone who reads a lot and it has a very positive connotation. The word wasn’t always positive and started life as a negative insult. “Worm” meant what we use worm to mean today when we are talking about a not very good person. “That guy is a real worm,” is not a positive thing to say. The worm in bookworm meant the same thing. It was used for someone who read too much, which was not seen as a good thing. And this is what I learned today.
Images By Lieven – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=41062299
Sources
https://www.merriam-webster.com/wordplay/is-the-meaning-of-bookworm-positive-or-negative
https://en.wikipedia.org/wiki/Silverfish
https://animals.mom.com/insects-eat-glue-books-5852.html