Insect Damage to Books — Bookworms, Silverfish, and Other Pests

The phrase “bookworm” is not merely metaphorical — insects have been boring through, eating, and nesting in books since the earliest manuscripts. Insect damage is one of the oldest and most persistent threats to book collections, and evidence of past insect activity is found in books of every period and origin. Understanding which insects attack books, what their damage looks like, how to prevent infestations, and how to treat affected books is essential knowledge for collectors and institutions.

The Insects

True Bookworms (Beetle Larvae)

The “bookworm” of literary tradition is actually the larval stage of various beetle species, primarily:

Furniture beetle (Anobium punctatum) — The most common wood-boring beetle in temperate climates. Its larvae bore through paper, cardboard, and wooden boards, leaving characteristic round exit holes (about 1–2mm in diameter) and tunnels filled with fine powdery frass (excrement).

Deathwatch beetle (Xestobium rufovillosum) — Larger than the furniture beetle, with correspondingly larger bore holes. More commonly attacks wooden shelving and structural timber, but can damage wooden book boards.

Drugstore beetle (Stegobium paniceum) and cigarette beetle (Lasioderma serricorne) — These beetles bore into a variety of organic materials including book bindings, paste, and paper.

Damage pattern: Round holes bored through pages, boards, and spines; tunnels through the text block; powdery frass in and around the book.

Silverfish and Firebrats

Silverfish (Lepisma saccharina) and firebrats (Thermobia domestica) are wingless, elongated insects that feed on:

• Paper (particularly sizing and coatings)
• Paste and adhesives
• Book cloth
• Photographic emulsions

Damage pattern: Irregular surface grazing — silverfish eat the surface layer of paper and cloth, leaving a characteristic irregular, scraped appearance without boring holes. They prefer starchy materials and sized paper.

Silverfish thrive in humid, dark environments and are nocturnal, making them difficult to detect until damage is visible.

Carpet Beetles (Dermestidae)

Carpet beetle larvae (particularly Anthrenus and Attagenus species) feed on:

• Leather bindings
• Cloth bindings
• Feathers, fur, and other animal-derived materials
• Sizing and adhesives

Damage pattern: Irregular holes and surface erosion in leather and cloth. Larvae leave characteristic shed skins (tiny, bristly casings) near feeding sites.

Termites

In tropical and subtropical regions, termites can cause catastrophic damage to book collections. Termites consume paper and wood, and a large colony can destroy an entire collection.

Damage pattern: Extensive destruction, often working from the inside out — a book may appear intact on the shelf but be hollowed out internally. Termites build mud tubes for travel and leave characteristic muddy deposits.

Cockroaches

Cockroaches feed on paper, adhesives, leather, and cloth. Their damage is often accompanied by dark brown excrement spots and a distinctive musty odor.

Damage pattern: Irregular surface feeding on paper and cloth, particularly on starchy materials. Cockroach excrement stains paper.

Booklice (Psocoptera)

Booklice (also called psocids) are tiny, soft-bodied insects that feed on microscopic mold growing on paper and bindings. They are indicators of excessive humidity rather than primary destructors, but large populations can damage the surface of paper and bindings.

Identifying Insect Damage

Active vs. Historic Damage

Active infestation — insects are currently present and actively damaging the book. Signs include:

• Live insects visible on or near books
• Fresh frass (powdery excrement) near bore holes or on shelves
• New damage appearing on previously clean areas
• Shed skins, egg cases, or webbing

Historic damage — insect damage that occurred in the past, possibly centuries ago. The insects are no longer present, and the damage is stable. Many older books show wormholes from long-departed beetle larvae.

The distinction matters: historic damage is a condition issue that affects value but does not require pest treatment; active infestation requires immediate intervention.

The Wormhole

The characteristic wormhole — a round tunnel bored through the pages of a book by beetle larvae — is one of the most recognizable forms of book damage. Wormholes may:

• Pass through only a few pages (if the larva was near the surface)
• Bore through the entire text block (if the larva traveled through the full thickness)
• Follow a more or less straight path or curve through the text block
• Show on covers and boards as well as text pages

Prevention

Environmental Control

Most book-destroying insects thrive in specific environmental conditions:

• Warm temperatures (above 70°F / 21°C) accelerate insect reproduction
• High humidity (above 65% RH) supports mold growth, which in turn attracts booklice and provides food for other insects
• Poor air circulation creates stagnant microclimates favorable to insects

Maintaining cool, dry, well-ventilated storage conditions is the most effective prevention strategy.

Cleanliness

Regular cleaning of bookshelves and storage areas removes the food sources (dust, mold, paper fragments) that sustain insect populations.

Inspection

Regular inspection of books and shelves for signs of insect activity — frass, shed skins, live insects — allows early detection and treatment.

Quarantine

New acquisitions (particularly books from estate sales, thrift stores, or overseas) should be inspected and, if possible, quarantined before being placed in the main collection. Insects can be transported in books and infest an entire collection from a single contaminated volume.

Integrated Pest Management (IPM)

Institutional collections use Integrated Pest Management — a systematic approach combining:

• Environmental controls (temperature, humidity, cleaning)
• Monitoring (traps, regular inspections)
• Physical exclusion (sealing gaps, screening windows)
• Treatment (targeted intervention when pests are detected)

Treatment

Freezing

Low-temperature treatment is the most common non-chemical method for killing insects in books:

• Seal the book in a polyethylene bag to prevent moisture damage
• Freeze at -20°F (-29°C) or below for at least 72 hours
• Allow to return to room temperature slowly (still in the bag) to prevent condensation

Freezing kills insects at all life stages (eggs, larvae, adults) if maintained at sufficiently low temperatures for sufficient time.

Anoxic Treatment

Anoxic treatment (oxygen deprivation) kills insects by sealing infested items in an oxygen-free environment (typically using nitrogen or argon gas) for a period of several weeks. This method is non-toxic and non-damaging to the books.

Chemical Treatment

Chemical pesticides are generally avoided for book treatment because they can:

• Stain paper and bindings
• Leave toxic residues
• Damage materials over time
• Pose health risks to handlers

When chemical treatment is necessary, it should be performed by professional pest control specialists experienced with cultural property.

Impact on Value

Wormholes in Older Books

For books from the 15th through 18th centuries, wormholes are a common and largely accepted condition issue. A 16th-century book with a few wormholes — particularly if they do not affect text readability — is valued according to all its other qualities, with the wormholes noted but not treated as disqualifying.

For modern books (19th century onward), wormholes are less common and more damaging to value because they indicate storage problems.

Severe Damage

Extensive insect damage — large areas of paper consumed, major structural damage to bindings — significantly reduces value regardless of the book’s age or importance.

Insect damage to books is a permanent record of the vulnerability of organic materials to biological attack. Prevention through proper environmental conditions is far more effective — and far less expensive — than treatment after damage has occurred.