Bookworms, insects and the teeth of time

Today the term bookworm has come primarily to mean a person with their nose always in a book. So I was a little surprised to learn something new about the more literal form of the word.

According to the Oxford English Dictionary the word bookworm has two meanings: (1) A person who enjoys or is devoted to reading (a "candle waster" as one 1601 writer complained); or (2)  Any of various insects that damage books; specifically a maggot that is said to burrow through paper and boards.

Surprisingly, there seems to be little agreement by non-entomologists on what kind of insects bore through books and consume the pages of history.  The larvae of wood boring beetles (anobiids) are mentioned (I've never seen this myself), as are moths, mites and booklice. Rarely does one hear about termites, though here in the U.S. our Reticulitermes flavipes has been known to partake in a good book when given the opportunity.  Indeed paper could and does make a very good bait for termites in the soil.

According to historian Stephen Greenblatt, bookworms as eaters of books have been the great fear of librarians and writers since before the Christian era. The

Illustration from Robert Hooke's 1665
book Micrographia shows a silverfish,
orabatid mite and pseudoscorpion.
Micrographia is available online for free.

silverfish is one.  In 1665 the British scientist Robert Hooke, working with one of the earliest and finest compound microscopes of his time penned the following description of a silverfish:

It is a small white Silver-shining Worm or Moth, which I found much conversant among Books and Papers, and is suppos'd to be that which corrodes and eats holes through the leaves and covers; it appears to the naked eye, a small glittering Pearl-colour'd Moth, which upon the removing of Books and Papers in the Summer, is often observ'd very nimbly to scud, and pack away to some lurking cranney, where it may the better protect itself from any appearing dangers.

If Hooke's charming anatomical description does not adhere to today's more precise terms, it still describes the silverfish reasonably well [some spellings corrected]:

Its head appears big and blunt, and its body tapers from it towards the tail, smaller and smaller, being shap'd almost like a Carrot....It had two long horns before, which were straight, and tapering towards the top, curiously ring'd or knobb'd, and bristled...the hinder part of the creature was terminated with three tails, in every particular resembling the two longer horns that grew out of the head

Later, he refers to silverfish (and other paper chewers) as representing the "teeth of Time", appropriate considering how much of history has been literally swallowed up by the silverfish and its ilk.

Silverfish are among the most primitive of the hexapods. Belonging to the insect order Thysanura, springtails and their cousins the firebrats are probably less known to most PMPs than, say cockroaches or ants.  Yet they are among the most common structural pests, especially in older structures. Unlike true insects, they do not go through metamorphosis and never seem to stop molting, even after reaching the adult stage. Instead, the nymphs look like miniature versions of the adults. Silverfish are roamers, and will travel throughout a structure to find food.  Once found though, they tend to stay close to their food source.

So on what do silverfish feed?  They seem to especially like paper that has been treated or coated with edible substances like starch, dextrin, casein, gum, and glue. Many of these materials are added to paper to influence its ability to absorb water or ink.  Glues used in books are also often natural in origin, and apparently tasty to silverfish.  But silverfish also digest cellulose, as shown experimentally by their preference for onion skin and cellophane (almost pure cellulose).  The well-known (to PMPs) entomologist Arnold Mallis showed that newsprint and cardboard and brown wrapping paper is almost never eaten by silverfish. They will feed on plant textiles like linens, cotton and lisle, however silk or wool is rarely eaten.

The Mallis Handbook notes that silverfish can be one of the more difficult pests to control, and elimination from a structure is not likely, short of fumigation.  This is largely because silverfish are able to hide throughout a structure in all its nooks and "cranneys"--as Hooke described them. It is certainly difficult, if not impossible, to treat all the hiding places of silverfish in a house. Desiccants applied to cracks and crevices where silverfish hide can be effective.  According to Frank Meek in the Mallis Handbook, silverfish are difficult to control using baits, though there may be limited value in applying some of the fine granular baits labeled for silverfish control.  Reducing humidity, vacuuming, sealing up valuable items, removing known food sources, and use of sticky traps are also listed as non-chemical controls for silverfish.

I have to admit that I have little practical experience with silverfish, except perhaps the few in my own office where they seem to relish small amounts of spilled cricket bait around my tarantula cage (crickets feed the tarantula). But now that I think of it, perhaps I had better spend more time considering how to discourage these critters before they devour some of my favorite books.

As Greenblatt noted, the ancients realized the battle against bookworms would be never-ending, and the best solution was to read the books (or parchments) regularly, and plan on replacing them when they inevitably decay. Of course your customers may not be happy with that, so its up to you to solve the puzzle of the bookworm 350 years after Robert Hooke first trained his microscope on the "silver-shining worms".

Acknowledgement to Stephen Greenblatt and his book: The Swerve: How the World Became Modern, for the inspiration for this post.