Adult moths themselves do not pose a threat to libraries. Like many insects, the damage is caused by the larval stage, or caterpillars, of certain species, driven by a specific nutritional requirement. These larvae are not targeting the paper itself in most cases, but rather the animal-based components historically used in book construction. Understanding this difference is the first step in protecting valuable collections from infestation.
The Direct Answer: Moths Versus Larvae
Adult moths, such as the webbing clothes moth (Tineola bisselliella), are generally harmless to books and textiles. Their primary function is reproduction, and they lack the chewing mouthparts necessary to consume materials like paper or binding cloth. The destruction is caused exclusively by the larvae, which are the feeding stage of the life cycle.
These worm-like caterpillars are equipped to digest keratin, a fibrous protein found in animal products that is indigestible to most other organisms. Keratin is a building block of wool, hair, and feathers, and the larvae specifically seek this protein for their development. Webbing clothes moth larvae graze along surfaces, sometimes spinning silken tubes or webbing as they feed.
Attractants in Book Materials
The vulnerable parts of a book are those derived from animal sources. Traditional bookbinding methods frequently utilized materials like leather, vellum, and parchment for covers, all of which are rich in animal protein. The glue used to hold the spine and pages together, especially hide glue or gelatin, is another significant animal-based attractant.
The paper itself, which is largely cellulose, is not the preferred food source for moth larvae unless it is heavily soiled or sized. However, the larvae will consume plant-based fibers like cotton or linen if they are stained with sweat, food, or body oils, as these provide supplementary nutrients.
Identifying Common Non-Moth Book Pests
When damage appears on books, the culprit is often not a moth but another common household pest, each leaving distinct signs.
Silverfish
Silverfish are small, wingless insects that prefer starchy materials like the dextrin and sizing used in paper and adhesives. Their damage is characterized by irregular, notched holes along the edges of pages, surface grazing that leaves a dull finish, and sometimes yellowish stains from their droppings.
Booklice (Psocids)
Booklice, also known as psocids, are tiny insects drawn to high-humidity environments where they primarily feed on microscopic molds and fungi growing on damp paper or bindings. They are an indicator of a moisture problem and generally cause only minor surface damage.
Carpet Beetle Larvae
Carpet beetle larvae, like moth larvae, seek out keratin and feed on leather bindings and animal-based glues. Their appearance is different from moths, often leaving behind shed casings with distinct long hairs.
Prevention and Storage Strategies
Controlling the environment eliminates the conditions and food sources these pests require. Since booklice and silverfish thrive in high humidity, maintaining a relative humidity level below 50% is crucial for prevention. Good air circulation and stable temperatures also discourage the growth of mold and fungi, a primary food source for psocids.
Books should be stored on shelves that are kept clean and dusted, avoiding damp, dark areas like basements and attics where pests flourish. Regularly inspecting and isolating new or used books before placing them with an existing collection prevents the introduction of eggs or larvae. Focusing on cleanliness and environmental management makes a book collection an inhospitable place for common library pests.