Silverfish are wingless, crawling insects represented by 250 species throughout the world. The name for the common household variety is Lepisma saccharina, which indicates the dietary staple of this critter: starch. They're not only one of the most primitive insects still around, but also can live up to six years in your home feeding on clothing, wallpaper, carpeting, books and dry foods. One way to get rid of these pests is to use boric acid.
Boric Acid Basics
Boric acid occurs naturally in seawater, volcanic ash, some plants and nearly all fruits. It is also found in several minerals, such as borax. You can find boric acid in hardware stores and in some pharmacies, where it may also be labeled as boracic acid or orthoboric acid. However, don't confuse boric acid with commercial borax. The latter is a disinfectant and laundry booster sold in the cleaning products section of supermarkets and will not kill silverfish.
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According to the U.S. Environmental Protection Agency, boric acid has been approved for use as an insecticide to control silverfish since 1948. Since that time, more than 180 pesticide products have been registered with the EPA that contain boric acid as the active ingredient.
The agency has also determined that boric acid and its compounds have a low toxicity in humans and are generally safe for residential use. Regardless, it has irritating properties. Avoid contact with your skin or mucus membranes, and do not ingest or directly inhale boric acid.
How Boric Acid Works
Liquid boric acid acts as a poison when ingested by insects, including silverfish. Powdered boric acid has the same toxic effect, but it also dehydrates the protective outer shell of the insect after coming into direct contact with it.
Using Boric Acid at Home
Use the powdered form of boric acid rather than the liquid form for a safer and more practical way to get rid of silverfish in your home. The powder is easier to contain and handle with less risk of spillage.
You can make a homemade boric acid bait for silverfish by combining one tablespoon of powdered boric acid with a cup of finely ground oats and a teaspoon of sugar. When this bait is placed in a container filled with scraps of torn paper, the silverfish will be attracted to the starch in the paper. Eating the paper will poison them since it will contain residual boric acid. The silverfish will also come into direct contact with the boric acid while crawling through the materials, which will dry out their skin.
Place the bait in areas where silverfish are most likely to be found, such as behind kitchen appliances, in attics or near electrical outlets and light fixtures. Regularly check the traps to replenish or relocate them.