Keeping squirrels out of your home is generally easier than getting them out once they've moved in and created a den in your attic. One commonly suggested method of repelling squirrels is the liberal use of mothballs. While there is some anecdotal evidence that the method may be effective, mothballs are not a sure fix and can be toxic to your home's inhabitants.
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Squirrels in Attics
Squirrels give birth twice a year, once in the summer and again in the late winter. In the summer, trees serve as acceptable dens. When the weather turns cold, females seek alternatives. Attics provide safety, shelter and comfort, the perfect environment for a squirrel to give birth and raise babies. Because squirrels are skilled climbers, accessing an attic is a simple matter of dropping onto the roof from a tree limb or climbing along wires that enter the house. If a squirrel cannot locate an opening, it will find a weakness in the structure and use its teeth to create an entrance.
Mothballs as a Repellent
Placing mothballs in an attic has been recommended as a way to discourage squirrels from entering. The suggested application rate calls for 1 lb. of mothballs for every 100 square feet of space. Some homeowners have reported success when using this method, but others say their success was temporary. Determined squirrels have been known to ignore the odor and create nests in an area of the attic as far away as possible from the fumes.
Mothballs as Pesticides
Mothballs are pesticides that include either naphthalene or paradichlorobenzene as the active ingredient. Both chemicals vaporize at room temperature, which produces an unpleasant odor and potential toxicity. Mothballs are intended for use in the control of clothes moths, and the instructions specify that they are to be used only in enclosed spaces such as a sealed garment bag or a container with a tight-fitting lid.
Very little exposure is required for an individual to smell mothball vapors. According to Dave Stone, a toxicologist with Oregon State University, all it takes are a few parts per billion in the air, which can result in a “persistent and noxious odor throughout the home.” If you can smell mothballs, you have been exposed to the chemicals. Naphthalene exposure has resulted in breathing difficulty, dizziness, headache and nausea. Pets in the home may experience ill effects as well. Although paradichlorobenzene is less toxic than naphthalene, it can still have unpleasant side effects.
Nontoxic ways to prevent squirrels from entering your home involve physically blocking all potential entrances. Use 1/2-inch hardware cloth to cover vents and chimneys. Repair damaged soffits, eaves and windows. Fill spaces around pipes and wires where they enter the house with expanding foam. To keep squirrels from using utility wires as a walkway to your home, slit a 2-foot section of 2-inch PVC pipe lengthwise and slip it over the wire. Squirrels will be unable to maintain their footing when the pipe rotates.