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archives society of alberta
December 1996    Volume 16 Number 3


by Rory M. Cory
Pest Control Officer, Glenbow Museum

Insects may be the last thing on your mind this winter, but while the snow builds up outside there may be an infestation lurking somewhere in your archives... If you've ever wondered why that 15th century leather bound volume isn't looking as new as it used to, or why those church records are a little more holy than they were, insects may be the reason why.

You say the thought is unappealing? Don't fear, pests that are harmful to archival material are not harmful to humans. They only target dead animal materials or collagen glues -- and in some cases the paper itself. This means that hardcover books with leather anywhere on the cover are particularly susceptible, but any volume bound with glue can be targeted, and all paper can serve as a habitat. Worse, anything in association with these habitats can be damaged by insects boring through in search of food. Some insects have been known to bore their way through tin to get to their objective!

Signs to look for. A certain indication of an infestation is, of course, actual insect material. This will likely not be in the form of adult carcasses, however, as most insects target archival material in their larval stage, and the larval stage lasts the longest, with only some larvae actually reaching adulthood. Hence, traces of larvae are the most common material found, and these are usually in the form of casings which the larvae moult several times over their growth stage. Casings are usually 0.5 - 1.0 cm long and are transparent elongated segmented "skins" with hairs visible under the microscope. Frass is the next most common insect trace. Simply put, it is insect excrement in the form of small pellets which are usually dark, but are often the colour of the material being eaten. Adults can also be found. Most of these types of samples filter down to the bottom of storage boxes.

Insects are masters of disguise, though, and it is easy to miss tiny insect matter. Incidental insect damage is thus another sign to look for. Irregularly shaped holes over 2 mm in diameter are a good indication. Depending on the type of material targeted, these can be a single hole, or a large area that has been entirely eaten away. For leather bindings in particular, graze lines are another sign to watch for. These are lines heading in a single direction which are not completely straight, indicating where the larva has eaten its way across the material. Separating book bindings can be a telltale sign of insects targeting binding glue.

The most common types of damaging insects that are found on archival materials in Alberta are Carpet Beetles. These spend most of their life stage in their larval form, so the most common signs are their casings (which are between 2 and 8 mm long) and frass. Carpet beetle casings are distinguished by their long "tails" (several hairs at one end of the casing).

Adult Black Carpet Beetle
Larval Black Carpet Beetle

Less common in Alberta, although still present is the Booklouse. These are mere specks to the naked eye, but if there are other signs of damage noted above, a microscopic search may reveal their presence. They are only 1-2 mm long and look like ants with distended abdomens. Damp and mouldy collections are potential food sources for these insects, so by keeping a collection dry and atmospheric conditions relatively stable, the incidence of these insects should be very low.


It is unlikely that Silverfish will be found on any collections from Alberta, but it is still possible, and it is a concern if a collection is being brought in from a damper, warmer climate. As a rule of thumb, anywhere south of the 49th Parallel is suspect (including Southwestern Ontario and the Maritimes). These insects like to eat glue (as in some book bindings) mainly, but also paper itself and even linen or cotton book bindings. They range between 3 and 13 mm in length and have a silvery coating that brushes off when handled.


Prevention. At the Glenbow Museum these problems have been avoided by means of a prevention program. To date there has been no infestation of the library and archives, and very little insect material indeed has been found there. All materials entering the museum must undergo visual inspection for evidence of insects, and depending on the material it is then frozen at -30 C for one week after which it is reexamined and then refrozen if any signs of activity remain. This is repeated until no traces of insect life are left. The freezing process is necessary because even if all visible insect remains have been removed, there could still be thousands of microscopic eggs present which cannot be removed manually. Freezing at the prescribed temperature will kill all insect life stages.

What to do in the event of an infestation. When preventative measures are not feasible, building seals are unreliable, or something just goes wrong, an infestation may occur. Staff should be trained to look for the above signs while examining archival materials, but a low maintenance monitoring system can also be set up. At the Glenbow this consists of a series of glueboard traps (available through any local pest control company) placed at regular intervals through the storage area. These should be checked bimonthly to see what insects have crawled into them. If anything is found, chances are that nearby materials have been infested. Further glueboard traps can be set up in the immediate area to pinpoint the infestation, or a visual examination can ensue. To reduce the amount of time the infestation has to spread, the latter course of action is preferable.

Once the infested materials are found, they should be isolated immediately (archival boxes sealed inside bags are sufficient) and then put through the above freezing process. If proper facilities are not available on site, cold storage facilities can often be rented, or cold storage trucks called "reefer" trucks can be brought on site.

Caught in time, infestations are relatively easy to control. With the recent replacement of toxic chemical fumigants with the freezing process, there is no risk to human health. If proper preventative measures are in place, however, infestations should not arise.

We all know how damaging light, water, hand oils and rough handling can be to archival materials. So the next time a patron brings a box of ratty looking papers to your attention, be sure you really do look closely "between the lines".


Edwards, Stephen R. et. al. (Ed.) Pest Control in Museums: A Status Report (1980). Association of Systematics Collections, 1981.

Milne, Lorus and Milne, Margery. National Audubon Society Field Guide to North American Insects and Spiders. New York, Alfred A. Knopf, Inc., 1996.

Strang, Thomas J.K. "A Review of Published Temperatures for the Control of Pest Insects in Museums" Collection Forum 8 (2), 1992, pp. 41-67.

Strang, Thomas J.K. "Guidelines for Museum Pest Insect Control - Low Temperature" Canadian Conservation Institute Note 3/2, 1993.

Ward, Philip R. Getting the Bugs Out: Museum Methods Manual 4. The Friends of The [British Columbia] Provincial Museum, 1976.