Silverfish

Perhaps unlike other insect pests in libraries, Silverfish thrive in
humid climates, and their lives can be effected by changes in humidity.

At the University of Florida, we've found that Boric acid -- besides
being messy, requiring the pest to traipse through it without apparent
incentive -- is rendered ineffective, over time, by the humidity in
which Silverfish thrive.  ... So not only is it messy, unattractive, and
physical separated from infested materials, but it also has to be
replaced relatively often with little or no bang for the buck.

Our Pest Control Division urges us to use silica gel as well.  Within
enclosed spaces, e.g., map cases, with low rates of air exchange, this
seems to work well, reducing humidity in the case and controlling
silverfish populations.  Silica, like boric acid, must be contained in
canisters separate from infested items, but unlike passive boric acid,
it alters the environment which sustains silverfish.  Silica, also like
boric acid, must be replaced periodically.  The interval between
replacement is longer for silica than boric acid, and silica can be
"reconditioned" (though not easily) for effective reuse.  (We use a dyed
silica together with white gel pellets to indicated needed change.)
Pellets must be replaced less frequently than powders, though powders
should effect desired change more quickly than pellets. (Given our
humidity problems and appropriate apportionment of silica, there seems
little danger that we will lower relative humidity below optimal levels
for storage of the paper or photographic materials.)

We have also determined that use of silica and other humidity controls
merely slow rates of population growth without also reducing and
maintaining low(ered) temperatures.  Temperature level, however, depends
upon the type of Silverfish infestation.  Lepisma saccharina, the most
common, the actual "silverfish", requires incubation temperatures above
72 degrees F (22 degrees C).  Other species, particularly those
identified in California, i.e., Ctenolepisma longicaudata, Ctenolepisma
urbana, and Ctenolepisma quadriseriata, require higher incubation
temperatures. In one of our infested collections, we attempted to
maintain temperatures between 65 and 70 degrees F while also
dehumidifying for a period of two weeks.

Our Pest Control Division also suggested use of simple home-made traps.
The traps, described below, seem to work wonderfully, but may also
represent a source of food for other insects which can escape them. The
trap is a small glass with smooth sides (a small guide ramp up the
outside, i.e., a piece of paper, wrapped around the outside) and
partially filled with flour.  (I have also mixed boric acid in my traps
at home to kill insects which might otherwise be able to escape.  I
imagine a mixture with silica powder might starve rather than poison the
insects.) Assuming your silverfish are attracted, and capture entire
populations traps would have to be tended and remain with infested
materials for 3 to 4 months minimum.

Erich J. Kesse
Preservation Office
University of Florida Libraries
904-392-6962
Fax: 904-392-7251

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                  Conservation DistList Instance 6:57
                    Distributed: Friday, May 7, 1993
                        Message Id: cdl-6-57-001
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