Beth Lindblom Patkus
A variety of insects and other pests attack binding materials, adhesives, and other substances in library and archival collections. Since some insects are attracted to the tight, dark places that abound in storage areas, and since many materials are handled infrequently, insects and other pests may do significant damage before they are discovered.
Libraries and archives have traditionally relied on pesticides for routine pest prevention and response to observed infestation. Pesticides often do not prevent infestation, however, and application of pesticides after the fact cannot correct the damage already done. Pesticides have also become less attractive because of a growing awareness that the chemicals in pesticides can pose health hazards to staff and damage paper-based collections. Newer extermination methods such as controlled freezing and oxygen deprivation have shown promise as alternatives for treatment of existing infestations, but like pesticides, they do not prevent infestation. Prevention can be achieved only through strict housekeeping and monitoring procedures.
Preservation professionals increasingly recommend a strategy called integrated pest management (IPM). This approach relies primarily on non-chemical means (such as controlling climate, food sources, and building entry points) to prevent and manage pest infestation. Chemical treatments are used only in a crisis situation threatening rapid losses or when pests fail to succumb to more conservative methods.
Most of the insect species likely to infest paper collections are attracted not by the paper itself but by sizes, adhesives, and starches, all of which are more easily digested than the cellulose that makes up paper. Some insects will also attack cellulose (i.e., paper and cardboard) and proteins (i.e., parchment and leather). Insect damage does not come solely from dining habits; collections are also damaged by tunnelling and nesting activities, and by bodily secretions.
Silverfish, firebrats, psocids (also called booklice), and cockroaches are among the most common library pests. Silverfish and firebrats can reach up to 12.5 mm in length; they feed on paper sizing, chew holes in paper (especially glossy paper), and damage book bindings and wallpaper to get to the adhesives underneath. They also feed on textiles, primarily rayon, cotton, and linen. They prefer dark, humid areas that are undisturbed for long periods of time. Psocids feed on microscopic mold growing on paper, and thus their presence usually indicates a humidity problem in the storage area. They are much smaller than silverfish and firebrats (about 1-2 mm), and may also feed on pastes and glues, but they do not produce holes in paper.
Cockroaches are omnivorous, but are especially fond of starchy materials and protein; they will eat book pages, bindings, adhesives, leather, and wallpaper. Cockroaches will chew holes in paper and bindings, but also can badly stain materials with their secretions. Cockroaches are thigmotactic, meaning that they like to contact a surface on all sides of the body; they seek very small crevices, between framed objects and the wall, etc.
The above discussion of library pests is far from exhaustive. Additional information on library and museum pests can be found in Harmon, Zycherman & Schrock, and Story, referenced at the end of this leaflet. Although other pests such as rodents may be encountered in libraries and archives, this leaflet will concentrate primarily on the prevention of insect infestations.
All insects go through a metamorphosis during their life cycle; their growth proceeds in a series of steps until they reach adult stage. Other stages include egg, larva, pupa, and nymph; not all insects go through all stages. For many insects, the larva stage is the most damaging since that is when the most feeding takes place, but others (such as booklice) also inflict damage in the adult stage.
It is important to remember that collections themselves are not the only source of food for insects. There is a huge spectrum of foodstuffs for insects and other pests in library and archives buildings. The most obvious attractant is human food waste and stored food in offices and kitchens, but there are many other less obvious food sources.
Dermestid beetles may attack leather and wool, including rugs. They may also be attracted by dead birds and/or abandoned birds nests. Some species of beetles feed on the pollen and nectar from flowering plants, while others eat shed hair and skin cells from humans and other animals. Dust mites, which are numerous and almost invisible, feed on this human dander.
Although some insects may not be a direct threat to collections, their presence may attract insects that do pose a threat. Some insects feed on the bodies of other insects. Most pests (insect and otherwise) are attracted by debris from human or other animal activities.
Since most buildings and collections offer a seemingly endless supply of food for insects and other pests, it is clear that the first priority for effective pest prevention must be to eliminate sources of food and strongly emphasize strict housekeeping.
Insect species require specific ranges of temperature, relative humidity, and other conditions in order to flourish. The first condition for their presence is the existence of openings in the building envelope through which they can enter. Once insects have entered a building, they seek out moisture, food sources, and undisturbed spaces for breeding.
Routes of Entry
Inadequately sealed windows and doors, or windows and doors that are left open routinely, can provide an entry point for insects. Cracks and crevices in walls or foundations or openings around pipes can also be an entry route. Insects can squeeze through extremely small openings. Vents and air ducts can provide an entry point for birds, rodents, and insects. Plantings close to a building provide an excellent habitat for insects, which may then migrate into the building through various openings. Insects also can be brought into the building in books and papers themselves.
Optimum temperature for many insects is between 68-86°F. Most insects will die if exposed to temperatures below 28°F or above 113°F for a period of time. Optimum humidity levels for their proliferation are generally between 60%-80%. 1 Insects need moisture to survive, and some (such as psocids and silverfish) thrive on high humidity.
Many insects are attracted to damp areas. Sources of water and potential insect habitats include water pipes running through collections, restrooms, kitchens, water fountains, custodial closets, and climate-control equipment. Standing water on a roof or in other locations can raise humidity levels and provide an excellent environment for insects.
Food waste in kitchens and offices provides sustenance for insects, particularly if it remains in a building and uncovered for long periods of time. Potted plants and cut flowers, water in vases and over-watered plants, dead and dying plants, and the nectar and pollen of flowering plants all encourage the presence of insects.
Some insect species that threaten collections thrive in small, dark, undisturbed spaces, in other words, in conditions that are common to storage areas. Insects will set up housekeeping inside dark, tight spaces (such as corrugated boxes), and are attracted to piles of boxes or other materials that are left undisturbed for long periods. Insects also live in quiet spaces like corners, the undersides of bookcases, and behind furniture. Dust and dirt help to provide a hospitable atmosphere for pests. Dead insects or insect debris can attract other insects. Dirt and clutter also make it difficult to see pests, so a problem may go unnoticed for some time.
Control of insect infestation requires elimination insofar as possible of potential insect habitats and food sources.
Integrated pest management strategies encourage ongoing maintenance and housekeeping to insure that pests will not find a hospitable environment in a library or archives building. Activities include building inspection and maintenance; climate control; restriction of food and plants; regular cleaning; proper storage; control over incoming collections to avoid infestation of existing collections; and routine monitoring for pests.
It is best to begin a formal pest management program with an initial survey of the building and all collection storage areas. Have there been any pest problems in the past? If so, what type of pest was involved and what materials were affected? What was done to solve the problem? Any potential insect habitats should be eliminated. There are several steps that can be taken to reduce the number of insects in a library or archive.
Routes of Entry
Windows and doors should be tightly sealed; weatherstripping may be necessary. Doors should not be propped open regularly. Openings around pipes should be sealed, as should cracks in the walls or foundation. Vents should be screened to keep out birds and rodents. A planting-free zone of about 12 inches should be maintained around buildings to discourage insects from entering. Plantings should be properly cared for and not over watered. The area around foundations should be graveled and graded away from a building to avoid basement flooding.
Climate should be moderate; conditions should be cool and dry; specifics depend on the needs of different materials. Temperature should be 68°F or lower, and relative humidity should be kept below a maximum of 50%. Maintaining climate conditions recommended for the preservation of books and paper will help to control insect populations.
Pipes in collections areas and other sources of water such as restrooms, kitchens, or climate-control equipment should be inspected routinely to guard against water leakage. Wrap sweating pipes with insulating tape. Close off unused drains or drainpipe openings. Roofs and basements should be inspected periodically to insure that there is no standing water or flooding. Where problems recur, frequent inspections are necessary.
Plants and cut flowers should be removed from the building. If this is impossible, plants should be well cared for and kept to a minimum; flowering plants should certainly be avoided. Avoid over watering and watch plants carefully for signs of infestation or disease. Food consumption should be confined to a staff lounge; staff should not eat at their desks. If functions that include refreshments are held in other spaces, all leftovers should be tightly sealed or removed by the caterers. Vacuuming and kitchen cleanup should be done immediately. All food should be stored in tightly sealed glass or metal containers or refrigerated, and a plastic garbage can with a tight-fitting lid should be provided for food waste. Trash should be removed from the building daily.
Collection storage areas (and other areas) should be cleaned routinely and thoroughly, at least every 6 months. All areas should be checked for signs of pests at least once a month. Look at collections for stains and signs of insect grazing (small holes in paper, or areas of loss on the surface of paper or bindings). Check window sills; under bookcases and radiators; on and behind shelves; and inside boxes and drawers for signs of insect activity. Look for small piles of dust, insect bodies, frass (insect droppings), egg cases, and live insects; clean up any insect debris immediately.
It is particularly important to develop strict procedures for dealing with newly acquired collections, since such collections have often been stored in attics or basements that are hospitable to pests.
Examine incoming material immediately to see if there is evidence of infestation. Work over a clean surface covered with blotter or other light paper. Remove all objects from storage or shipping enclosures and look at the binding, pages, and hollow (if any) in books. Examine frame backings and mats, wrappings, and other accompanying materials. Look for live creatures, insect droppings, larvae, or bodies.
Transfer materials to clean archival boxes until you can process them. If possible, isolate rehoused, incoming materials in a space away from other collections until processing. Space that will provide preservation conditions is cool, dry, clean, outfitted with shelving, etc., to discourage mold and insects. Throw the old boxes away unless they are archival quality and you are absolutely certain they are clean.
The clean archival boxes can be used over and over for this temporary holding use as long as the contents and boxes continue free of evidence of insects. Ideally, of course, incoming material should be processed and rehoused in its permanent enclosures promptly. Realistically, processing may be delayed, and the interior of boxes should be inspected routinely at least every few weeks. A tent or motel-type sticky trap can be placed on a side wall inside each box to improve monitoring.
If there is evidence of insects, talk to a preservation professional for detailed advice before proceeding further. Materials can be vacuumed thoroughly (assuming the objects are not deteriorated or fragile) through a nylon or other soft screen, using a high-filtration vacuum. Discard both filter and disposable bag outside the building or in a sealed container which is provided for food wastes and is emptied daily.
Effective implementation of a pest management program requires routine monitoring of pest activity. Routine monitoring using traps provides information about the type of insect(s), their entry points, the number of insects, where they are taking up residence, and why they are surviving. This information allows for identification of problem areas and development of a species-specific treatment program.
The most commonly used insect traps are sticky traps, available from most hardware and grocery stores. Several types are available: flat traps, rectangular box-shaped traps (motels), and tent-shaped traps. Many conservators recommend the tent traps as the easiest to handle. Whatever type and brand is chosen, consistency should be maintained so that data can be interpreted accurately.
The basic procedure for monitoring is as follows: 1) identify all doors, windows, water and heat sources, and furniture on a building floor plan; 2) identify likely insect routes, and mark trap locations on a floor plan; 3) number and date the traps; 4) place the traps in the area to be monitored, as indicated on the floor plan; 5) inspect and collect the traps regularly; and 6) refine trap placement and inspection as necessary, according to the evidence collected. Relocate traps (if initial results are negative) and try again.
If infestation is suspected in a particular area, place traps every 10 feet. Care should be taken to insure that traps do not come into contact with collection materials, since the adhesive can cause damage. Checking the traps 48 hours after placement will identify the area most seriously infested. Traps should be inspected weekly for at least three months and should be replaced every two months, when they are full, or when they lose their stickiness.
Documentation is essential; monitoring will be useless without it. The number of insects, the types of insects, and their stage of growth should all be recorded for each trap. Dates and locations of trap replacements should be noted. Detailed records should also be kept of any other evidence of activity, such as live or dead insects or their droppings.
Once insects have been trapped, they must be identified to determine what threat they pose to collections. There are several good books with drawings and descriptions of common library and archives pests; these are listed in the bibliography. An excellent resource for identification is the local or state Agricultural Extension agency, which will usually identify insects free of charge (the insect must be sent to them, and the entire body must be intact). Other potential resources include the biology department of a local university or a local history museum with an entomologist on staff.
It is important to remember that sighting one or two insects is an occasion for monitoring to determine the extent of the problem; it is not necessarily a crisis situation. In the past, insect sightings often occasioned an indiscriminate use of pesticides.
If a serious insect infestation occurs, or if insect problems do not respond to the preventive techniques discussed above, direct treatment for insect infestation may be necessary. This strategy should be used as a last resort. Both chemical and non-chemical treatments are available; non-chemical means should be used wherever possible.
Pesticides are divided into categories, depending on the way they are used and their physical state.
Common chemical treatments used to control insects include aerosol sprays; attractants (which lure insects into traps, sometimes killing them); baits and pellets (which are eaten by the insects); contact and residual sprays (normally sprayed into cracks and crevices; these kill on contact and/or by absorption of the pesticide when the insect walks through the residue); dusts (e.g., boric acid or silica dust, which dehydrate insects or interfere with internal water regulation); fogging concentrates (these use equipment that suspends a pesticide and oil formulation in the air); fumigants (these expose infected material to a lethal gas); and residual and vapor pest strips (the insect absorbs pesticide by walking across residual pest strips, while pesticide evaporates from vapor pest strips to become a fumigant). Repellents (such as mothballs) are also sometimes used; these are meant to discourage rather than kill insects.
Fumigants are among the most toxic of pesticides; other pesticides are usually suspended in a liquid and sprayed, so that they tend to settle out of the air. Fumigant gases remain in the air and can easily spread over a wide area. Ethylene oxide (ETO), a gaseous fumigant, was commonly used in libraries and archives until the 1980s; many libraries had their own ETO chambers. ETO is effective against insect adults, larvae, and eggs. It poses serious health hazards to workers, and there is evidence that ETO can change the physical and chemical properties of paper, parchment, and leather. Acceptable limits on ETO exposure have been steadily lowered by the government, and most existing ETO chambers in libraries cannot meet these restrictions. Some residual ETO remains in treated materials, and little is known about the long-term risks to collections and staff from off-gassing toxins. ETO should be used only as a last resort; materials should be sent to a commercial facility and allowed to off-gas for at least several weeks before being returned to the library or archives.
In general, fumigants and other pesticides can cause long- and short-term health problems, ranging from nausea and headaches to respiratory problems to cancer. Many chemical treatments may cause no ill effects at the time of exposure, but may be absorbed into the body to cause health problems years later. Many of the chemicals also damage the treated materials and no chemical treatments provide a residual effect that will prevent reinfestation. Growing awareness of the risks has brought about increased emphasis on non-chemical pest-control methods.
A variety of non-chemical processes for exterminating insects have been explored. The most promising are controlled freezing and the use of modified atmospheres. Methods that have not proved as successful include the use of heat, gamma radiation, and microwaves.
Controlled freezing has been undertaken in various institutions over the past 15 years, and reports on its effectiveness have been largely favorable. Freezing is attractive because it involves no chemicals and thus poses no hazard to library staff. It can be used on most library materials and does not appear to damage collections (according to existing literature on experimental efforts), but research into this question is not yet complete. Very fragile objects, those made from a combination of materials, and artifacts with friable media should probably not be frozen; a conservator should always be consulted before any method is chosen.
Materials can be treated in household or commercial freezers, blast freezers, or controlled-temperature and humidity freezers. It is necessary to bag and seal items unless a freezer with specially controlled temperature and humidity is used. Bags must be sealed immediately to prevent insects from escaping. Some institutions box materials and then bag them. Bagging protects objects from changes in moisture content during defrost cycles and from condensation on cold books when they are removed from the freezer.
It is essential to guard against freeze resistance; some insects can acclimate to cold temperatures if they are kept in a cool area before freezing or if freezing happens too slowly. Research is incomplete in this area; it is not known if common library pests are able to develop freeze resistance.
In the absence of definitive data, material must be kept at room temperature until freezing begins. Items should not be packed too tightly within a freezer, since this can slow the freezing process. Most important, material should be frozen quickly. Freezer temperature should reach 0°C within 4 hours and -20°C within 8 hours. The most commonly reported successful treatments have been carried out at -29°C for a period of 72 hours. 2 It is unknown whether higher temperatures for a shorter time would be equally effective; there are reports that 20°C for 48 hours has also been used with success. 3
Collections should be slowly thawed (brought up to 0°C over 8 hours) and brought up to room temperature. The entire process should then be repeated to insure effectiveness. Objects should remain bagged (some institutions leave them bagged for 6-8 months) until monitoring in the space indicates that the insect problem has been solved. Detailed documentation of each phase of treatment should be maintained.
Like chemical treatments, freezing provides no residual benefits. If collections are not returned to a well maintained storage area, reinfestation will almost certainly occur.
Modified atmospheres have been used widely in the agricultural and food industries to control insect infestation. The term refers to several processes: decreased oxygen, increased carbon dioxide, and the use of inert gases, primarily nitrogen. Various experiments with modified atmospheres have been undertaken by cultural institutions over the past 10 years, with generally successful results. Modified atmospheres show great promise, but additional research is needed to determine optimum exposure times and methods for particular types of insects. There appears to be no obvious damage to collections, but little research has been done on long-term effects. There is potential danger to staff from exposure to high levels of carbon dioxide, if that is used, but there are no residual effects on collections.
Modified atmospheres can be applied 1) in a traditional fumigation chamber or a portable fumigation bubble or 2) in low-permeability plastic bags. With a chamber or a bubble, materials are prepared for treatment (quarantined, documented, and loaded into the treatment chamber), air is evacuated from the chamber, and carbon dioxide (generally about 60% concentration) or nitrogen (to achieve an atmosphere of less than 1% oxygen) is introduced. Once the desired atmospheric concentration is reached, conditions are maintained at a specific temperature and relative humidity for the required amount of time.
Once treatment is finished, the vacuum is released, the carbon dioxide or nitrogen is removed, the chamber is aerated, and materials are removed to a quarantine area so that the effectiveness of treatment can be assessed. The process for treating materials in low-permeability plastic bags is similar, except that materials are sealed in bags with an oxygen scavenger that will reduce the oxygen level in the enclosure to less than what is needed for insect respiration. In some cases, the bags are purged with nitrogen before sealing.
In the tests conducted thus far, a variety of exposure times, temperatures, and relative humidities have been used. Since requirements for achieving an acceptable kill rate seem to vary according to the type of insect being exterminated and the type of process being used, there are not yet any generally-accepted guidelines for the application of modified atmospheres. Always contact a preservation professional for advice before proceeding with modified atmosphere treatment.
Heat can effectively exterminate insects; it has been used widely in food processing and medicine. A temperature of 140°F for at least one hour will kill most insects. Heat should not be used to eliminate insects from paper collections, however, because heat at the levels needed to kill insects greatly accelerates oxidation and paper aging; materials can become brittle and otherwise damaged.
Gamma radiation is used to sterilize cosmetics, food and agricultural products, medical supplies, and hospital and lab equipment. It poses some danger to personnel during treatment, but there is no residual radiation in the treated material. Gamma radiation can be effective against insects, but the minimum lethal dose for various species is still unknown and is affected by variables such as climate conditions and the nature of the infested material. Most important, research has shown that gamma radiation may initiate oxidation and cause scission of cellulose molecules; it has the potential to seriously damage paper-based materials. There is also a cumulative effect from repeated exposures. As a result, gamma radiation is not recommended.
Rumors about the effectiveness of microwaves for killing insects have circulated in the library community over the past several years. Microwaves are used successfully in the food, agricultural, and textile industries to control insects, but this strategy is not recommended for library collections. Microwaves have a limited penetration, and may not penetrate thick books. Their effectiveness also depends on the type of insect and the intensity and frequency of the radiation. Microwave ovens vary in intensity, so it is extremely difficult to determine standard times and temperatures for treatment. The primary argument against microwaves is the danger of damage to treated materials. Evidence from a variety of experiments indicates that pages and covers can scorch; metal attachments like staples can cause arcing; and adhesives can soften, causing pages to detach from their bindings in certain books.
Freezing and modified atmospheres currently show the most promise as alternatives to traditional pesticides. They remain experimental until more research has been done, however, so a preservation professional should be consulted before undertaking either treatment.
Library and archival collections can be threatened by a variety of pests that damage paper-based and other materials. The method of pest control least damaging to collections and staff involves preventive measures and regular monitoring. If infestation does occur, treatment should be tailored to the specific insect species and the type of material that is infested. Chemical treatments should be avoided except as a last resort. Emerging technologies such as blast freezing and modified atmospheres have significant potential as alternatives to chemical control.
"Integrated Pest Management." Audiovisual Department, Université du Quebec à Montréal and Canadian Conservation Institute and Centre de Conservation du Québec. 1995. Videotape, 22 minutes. A professionally produced video that provides good basic information for museums and archives. Comes with a short, informative booklet that gives the key points and suggests further reading.
Canadian Conservation Institute. "Preventing Infestations: Control Strategies and Detection Methods," and "Detecting Infestations: Facility Inspection Procedure and Checklist." CCI Notes 3/1 and 3/2. Ottawa: CCI, 1996. 4 pp. and 3 pp. Short leaflets written primarily for museums providing general information about monitoring with traps and inspecting a building for infestation.
Jessup, Wendy Claire. "Integrated Pest Management: A Selected Bibliography for Collections Care." February 1997. An excellent annotated bibliography that covers museum, library, and archival pests; integrated pest management methods; the effects of pesticides on collections; and occupational safety and health. Available at http://palimpsest.stanford.edu.
Odegaard, Nancy. "Insect Monitoring in Museums"; and Dale Paul Kronkright. "Insect Traps in Conservation Surveys." Both in WAAC Newsletter 13.1 (January 1991): 19–23. Both articles offer practical tips for monitoring insect populations using various types of traps. Available online at: http://palimpsest.stanford.edu/waac/.