I recently learned that some people have been using mothballs to deter things like snakes, squirrels, and moles in their yard. I've even been told by people that their pest control person suggested it to them. Ugh. Not only are mothballs toxic, but it's unlawful to use them in this way.
It's important to know that mothballs are toxic, so you will be putting a toxin down around your home that will give off vapors for months. Those vapors are insecticide and it's not healthy to breathe them in. According to the National Pesticide Information Center, using mothballs outside can harm children, pets and other animals. Mothballs are regulated by the EPA, and the package contains instructions on exactly how you can legally use them. Using them in your yard as snake repellent is not a legal way to use them, and it's toxic to you, your family, and the animals around your home, including pets. Breathing the vapors has been linked to lung and eye irritation, as well as cancer. In other words, it is against federal law to use moth balls for anything other than the intended purpose expressed on the package, because they are so harmful to people and animals.
Moth balls, according to the package directions, can only legally be used inside air tight storage containers, so that the harmful toxic vapors don't leak out. It is unlawful to use mothballs other than for their intended purpose, as stated on the package. Using them outdoors as snake repellent (or for any other reason) can get you a $10,000 fine, according to the Florida Department of Agriculture and Consumers Services.
Please, don't use mothballs for anything other than in airtight containers, which is their intended purpose. And if someone suggests to you that they be used outdoors, please inform them that it's not only harmful, but doing so is subject to a hefty fine, because it's unlawful to use them like that. We must work together to protect the environment from such harmful substances. There are better ways of keeping things like snakes out of your yard, if you feel you must do so (including Snake-Be-Gone at Lowe's, cutting back shrubs, cleaning up yard debris, etc.). Mothballs should never be used outdoors. Never.