Books and other paper-based materials are susceptible to various insect pests because they contain organic substances that serve as an attractive food source. Paper is primarily cellulose fibers, and bindings often utilize starches, dextrin, or animal-based glues. These materials provide the necessary carbohydrates and proteins for many insects to survive. Identifying the specific pest responsible for the damage is the first step toward safeguarding a collection.
Primary Pests Targeting Paper and Starch
The most common culprits for direct consumption of book materials are small, wingless insects known for their appetite for starchy and cellulose-rich items. Silverfish, belonging to the order Zygentoma, actively seek out the cellulose in paper and the starches found in adhesives and coatings on the pages. They thrive in dark, damp environments with high humidity, often going unnoticed until their damage becomes extensive.
Silverfish are relatively small, measuring about 12 to 19 millimeters long, and leave behind distinct signs of their feeding activity. They use their mouthparts to graze on the surface of paper, which results in irregular holes, indentations, and light-colored, de-glossed areas where the finish has been removed. This scraping action often removes printed text, leaving behind a characteristic skinning on the page surface.
A related insect, the booklouse (psocid), is much smaller—typically only 1 millimeter in length—and does not directly consume the paper’s cellulose. Booklice feed primarily on the microscopic mold and fungi that grow on damp materials in highly humid conditions, signaling an underlying moisture problem. They can cause minor damage by scratching the surface of the paper while eating the mold, sometimes leaving faint discoloration. The presence of booklice, which look like tiny, pale specks, often indicates humidity levels are above the 75% threshold needed to support mold growth.
Another pest, the firebrat, causes similar grazing damage to silverfish as it consumes cellulose-based materials and binding adhesives. Firebrats prefer much warmer, humid environments than silverfish, making them a problem in areas with high temperatures, such as near furnaces or hot pipes.
Structural Borers and Tunneling Insects
Another category of pests causes severe, deep-seated structural damage by boring directly into the book block. The term “bookworm” generally refers to the larvae of certain beetles, such as the Drugstore, Cigarette, or Deathwatch beetles. It is the larval stage, not the adult insect, that is responsible for creating the destructive tunnels.
Adult beetles lay eggs in crevices, and the resulting larvae bore through the text block, consuming starch and animal-based glues. As the larvae mature and exit the book as adults, they leave behind tiny, round holes that penetrate deep into the material. The damage often includes a fine, powdery dust, known as frass, which is a mix of insect excrement and powdered book material.
Termites are the most destructive structural pest, as they consume any material containing cellulose, which includes every part of a book. Subterranean termites, in particular, can tunnel from the ground up through shelving and into stacks of books, hollowing out pages and covers. The damage is often catastrophic, characterized by extensive internal tunneling that leaves behind hollowed-out sections of paper.
Pests That Damage Through Contamination and Shelter
Some insects cause damage not by actively consuming the paper itself, but by using the books for shelter or by contaminating them with waste products. Cockroaches are opportunistic feeders that will chew on paper and cloth bindings, especially those soiled with food residue or grease. They are particularly drawn to the starch-based glues and paste used in older book construction.
The primary damage from cockroaches comes from the stains they leave behind, which include dark, smeary fecal spots and oily secretions. The American cockroach can leave a brown liquid smear known as atar, a pheromone often found on the edges of books. These stains can permanently discolor and degrade the paper, and the moisture they introduce can also encourage mold growth.
Reading the Damage: Identifying Specific Infestation Signs
Identifying the specific pest responsible for damage depends on a careful examination of the physical signs left behind. Damage from silverfish and firebrats appears as irregular, shallow scraping and loss of print on the surface of pages, often accompanied by yellow-brown stains from their scales or feces. This type of damage is typically found along the edges or on the covers of the book.
The presence of fine, powdery sawdust, or frass, near a book’s spine or covers is a strong indicator of an infestation by beetle larvae. These structural borers leave behind exit holes that are small, distinct, and circular, often going through multiple pages.
By contrast, booklice damage is characterized by extremely superficial scratching or translucent patches on the page surface, primarily associated with mold growth. Extensive internal tunneling, hollowing out large sections of the text block, or the presence of mud-like tubes near the book are definitive signs of a termite infestation. Dark, smeary stains, especially on the top or side edges of the book block, are the telltale sign of cockroach activity.