The term “bookworm” is a collective name for the larvae of various insects that feed on the materials found in books, not a single species. These pests pose a significant threat to collections because they consume the organic components that make up paper, bindings, and adhesives. Understanding the specific insects involved and the nature of the damage they inflict is the first step toward effective management and protecting a library from infestation.
Identifying the Biological Culprits
The most destructive “bookworms” are the larval stages of certain beetles, responsible for the deep, tunneling damage commonly associated with the term. The larvae of the Drugstore beetle (Stegobium paniceum) and the Cigarette beetle (Lasioderma serricorne) are common culprits, boring directly into the text block after the adult lays eggs in accessible crevices. These beetle larvae look like tiny, pale grubs and chew channels through multiple pages of a book while seeking nutrients.
Other insects also target the organic materials within a collection. Silverfish (Lepisma saccharina) are wingless insects that prefer dark, damp conditions and feed on the starch and cellulose in paper and glues. Their feeding is characterized by shallow grazing on the surface rather than deep boring, often leaving behind irregular holes and a “skinned” appearance on paper.
Booklice (Psocids) are minute, soft-bodied insects frequently found near books, though they are not true lice. These insects do not consume paper directly but instead feed on the microscopic mold and mildew that grow on books stored in high-humidity environments. Their presence is an indicator of environmental conditions conducive to a fungal and pest problem.
Termites and cockroaches also contribute to book damage by consuming cellulose and starchy glues. Termites are capable of hollowing out entire sections if an infestation is left unchecked.
How Bookworms Damage Collections
The damage inflicted by these pests stems from their consumption of the various organic compounds used in book construction. Paper is primarily cellulose, a carbohydrate many insects can digest, while covers may contain leather or cloth. A particularly attractive food source is the starch-based glue and paste historically used in bookbinding, which provides a high-energy meal for many beetle larvae and silverfish.
The visual signs of an active infestation vary depending on the pest but often include distinct boreholes that penetrate through several pages. Beetle larvae create circular tunnels, and they leave behind a fine, powdery excrement known as frass, which is often visible near the exit holes or between pages. Silverfish, conversely, leave behind surface etchings, yellow stains, and small, irregular losses along the edges of pages.
Environmental conditions make a book collection susceptible to attack. High humidity, typically above 60%, encourages the growth of mold and mildew, which in turn attracts booklice and creates a more palatable food source for other pests. Elevated temperatures accelerate the life cycle of these insects, increasing the rate at which they reproduce and destroy materials. A damp, warm, and undisturbed environment effectively creates an ideal breeding ground for nearly all types of book-damaging pests.
Protecting Books from Infestation
Protecting a library from infestation involves maintaining strict environmental control. Books should be stored in a space where the temperature remains stable, ideally around 70°F, and the relative humidity is kept below 60%, with an optimal range near 50%. Using a dehumidifier or air conditioning helps to discourage the mold growth that attracts booklice and makes the materials less appealing to other pests.
Proper storage also involves physical barriers and regular housekeeping to eliminate potential food sources. Books should not be stored in damp basements or hot attics, which are prone to environmental fluctuations and pest harborage. Regularly cleaning bookshelves removes dust and insect eggs, while avoiding eating or drinking near the collection prevents crumbs that could attract rodents and cockroaches.
If an isolated book is suspected of having a localized infestation, it should be immediately isolated in a sealed plastic bag to prevent the spread of pests. For small, non-valuable items, a common treatment protocol involves placing the sealed book in a freezer at 0°F (-18°C) or lower for a minimum of four days to kill all life stages of the insect. This freezing process must be executed carefully to prevent moisture damage, and professional consultation is advisable for rare or fragile volumes.