Moth balls are solid insecticides, and are very effective at killing fleas and other pests. However, using them in such a manner is dangerous to other living beings, including pets, small children and adults.
Moth balls are a kind of insecticide that volatilizes, or changes its physical state directly from solid to gas. Moth balls are meant to be used in closed containers so that the fumes from the insecticide only cause harm to any pests inside the container. When placed in open containers, on the ground, or to swab pets infected with fleas, mothballs can cause irritation, nausea, headaches and diarrhea in humans, and neurological symptoms including seizures in pets. Ingestion of mothballs by a curious pet causes vomiting and liver failure. Long-term exposure is linked to nasal cancer in humans.