Mothballs are branded as a pesticide that is used to kill moths and other fiber eating pests. Most brands of mothballs contain the chemicals naphthalene or paradichlorobenzene which is highly toxic to humans and animals. Although mothballs start as a solid round ball or flake at room temperature, they eventually change into a gas and fumes. If you can smell a mothball it means you have been exposed to the toxic fumes. Pets have been known to mistake them for food and eat them resulting in serious side effects and even death. As well as being ineffective to repel woodchucks, mothballs also contaminate soil and water.