US Coins

Pest seeks out album mold

A book louse, which a collector found among his coin albums kept in a locked safe, is shown beside a Lincoln cent.

Image courtesy of joefro from Collectors Universe U.S. Coins Forum.

This month I am responding to a query recently posted on the Collectors Universe U.S. Coins Forum. The collector wrote:

“I got into my safe today for the first time in quite a while. To my surprise, there were a bunch of tiny bugs crawling around in there. The safe is a solid seal, no way that they were climbing in or out so they must have been breeding in there. They are extremely small, clearish brown and they look like aphids. They seem to be concentrated the most around my Dansco albums. The safe currently houses the Dansco albums, personal papers and a pack of silica gel. ... I am thinking of putting them into the freezer for a day or two. Has anyone seen this before?”

A fellow participant on the forum suggested that the bugs might be book lice. This, given his description, is a good guess. In later postings, the collector posted images of the insects he found (one illustrated). As I am not an entomologist, I asked my colleagues at Insects Limited Incorporated ( to confirm my identification. The insects are, indeed, book lice.

Book lice are psocids, a member of the insect order Psocoptera. They are small and pale to transparent in color. The presence of psocids indicates a humid environment. Psocids are omnivores, but research has shown that they are particularly fond of mold. Book lice do not eat books or paper; they feed on the often microscopic mold that can grow on paper.

The best way to control and eliminate psocids is to create an inhospitable environment for them. Mold grows at a relative humidity (RH) of 70 percent or higher. Keeping the RH at 50 percent or lower will eliminate the mold growth that attracts the psocids. As the collector had a sachet of silica gel in the safe, he may have been trying to keep the RH down for the sake of his coin collection. The silica gel is likely no longer conditioned to maintain a lower RH. Determining the RH level that the sachet is now conditioned to is fairly straightforward, providing the collector has the right equipment. Seal the sachet in a plastic bag along with a recently recalibrated hygrometer. Wait an hour or so and take a reading without opening the bag.

Freezing the Dansco albums and the papers in the safe will kill the bugs. It will not, however, kill any mold growing on these items.

To freeze, place the items in plastic freezer bags and seal tightly. Freeze these items to a temperature of at least -4 F (-20 C) for one week. This will kill all stages of the insect (i.e., eggs, larvae and adults). After one week, remove the bags from the freezer and allow them to come back to room temperature before opening the bag. Any condensation that forms should form on the outside of the bag. In the meantime, the collector should thoroughly vacuum the interior of the safe to remove any insects, eggs or larvae left behind.

Alternatively, the collector could purchase new albums and discard the infested ones. If he takes this approach, I would still recommend that he freeze the remaining papers from the safe and clean it thoroughly. After the freezing treatment is completed it is recommended that the items be examined under magnification to ensure that no bugs are left on them. Removing any bugs killed by the treatment will prevent false alarms in the future.

Susan L. Maltby, Toronto, is a private conservation consultant, with an interest in numismatic preservation.

Community Comments