Integrated Pest Management
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
LIBRARY AND ARCHIVES PESTS
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 tunneling and nesting activities, and by
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.
WHAT DO PESTS EAT?
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
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
HABITATS AND BREEDING HABITS
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%.
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; weather stripping 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
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
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
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
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
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.
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
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
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
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.
SUMMARYLibrary 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.