Dealing With Silverfish

Silverfish are primitive, wingless insects that have adapted to living with people. They feed on most human foods, as well as starch, glue, paste, paper products and fabrics, even certain synthetic fabrics. Silverfish can travel throughout a building looking for food, and will commonly damage books, wallpaper, fabrics, photographs and paper products.

They typically avoid light, preferring to live in the dark, and infestations of silverfish usually pass unnoticed or are ignored until the population becomes large and widespread. At that point, of course, silverfish are difficult to control.

Moisture and Silverfish

The common silverfish requires high humidity and warm temperatures to develop. It prefers a relative humidity of 75% to 95% and a temperature between 70°F and 80°F.

A silverfish infestation is often an indicator of excessive humidity and moisture problems somewhere in the building. Typical causes of moisture problems include the following:

Roof leaks into the loft or ceiling voids, particularly in the case of flat roofs;
Moisture trapped in subflooring under sheet vinyl floors and similar nonpermeable floor covering;
Moisture trapped in exterior walls because of moisture infiltration;
Condensation on water lines, air conditioning lines and vents, and on improperly installed (reversed) insulation;
Plumbing leaks.

Silverfish Control

The primary control tactic for a widespread silverfish infestation is to dry out all infested areas so that the silverfish are unable to reproduce and develop successfully. Unfortunately, there is no immediate fix: the drying process can take months or even longer. You can however, suppress silverfish populations in critical areas:

Remove and discard old stacks of newspapers, magazines, papers, boxes of clothes for donations, etc. Clothing in infested wardrobes, dressers or boxes should be washed or dry cleaned.
Infested books and other items can be placed in a large freezer at 0°F for four to seven days. The books should first be wrapped tightly in plastic, and the plastic should be left on during the thawing process to prevent condensation damage.
Apply a baseboard insecticide spray around the perimeter of a room as a barrier to intercept silverfish moving from the wall voids and going under the baseboard into the room.
Apply dust into infested voids in ceilings and walls. Because silverfish move long distances through voids and pipe runs, it is probably not practical, or even possible, to treat every void in the floors, walls and ceilings where silverfish could be located, so you'll have to be selective.
Treat cracks and crevices in infested rooms with a residual as though you were treating for Brown-Banded cockroaches.
Pest-proofing critical rooms can also reduce silverfish infiltration to some extent. Caulk any obvious openings and cracks, and consider pulling up the edge of wall-to-wall carpeting to caulk under the baseboard.
Where you have a ceiling access panel in a room with heavy silverfish pressure, consider installing a light in the ceiling void.

Silverfish do not like bright light, and there has been some success moving silverfish out of restricted areas with this technique.

It is important that you understand that it is unlikely that you will see results overnight. Control of a widespread outbreak of silverfish is a long-term project, requiring moisture problems to be corrected and the building dried out. Until that happens, control actions are just temporary.

SDA Pest Control, "Long Acre", Bluntisham Road, Needingworth, St. Ives, Cambridgeshire
01480 465684