Mothballs are solid blocks of pesticide designed to protect fabrics from insect damage. These small, waxy products contain a high concentration of one of two primary active ingredients: naphthalene or paradichlorobenzene (PDCB). Although often mistaken for a general animal repellent, their use is strictly regulated based on their intended purpose and toxicity. The widespread practice of using them to deter nuisance animals is an off-label application that is ineffective and illegal.
The Registered Use of Mothballs
Mothballs are legally registered by the Environmental Protection Agency (EPA) as insecticides, not as general animal repellents. Their sole intended purpose is to kill clothes moths, specifically the larvae of species like Tineola bisselliella and Tinea pellionella, which feed on natural fibers. The product label directs users to place them in tightly sealed, airtight containers, such as garment bags or trunks.
This sealed environment is necessary for the chemicals to work. The active ingredients transition from a solid directly into a toxic vapor through a process called sublimation. In a closed space, these fumes build up to a concentration lethal to the moth larvae, protecting stored clothing. Any use outside of this specific application outlined on the product label is considered misuse.
Wildlife Targeted in Misapplied Use
Despite their specific registration, mothballs are frequently and ineffectively used against a wide range of nuisance wildlife. People commonly target smaller rodents, placing mothballs in attics, crawl spaces, or sheds to deter mice, rats, and squirrels.
Larger mammals are also common targets for this misuse, with mothballs scattered in gardens or under decks to repel animals like raccoons, skunks, and deer. Similarly, the strong, pungent smell of naphthalene or paradichlorobenzene is mistakenly thought to be a deterrent to reptiles, leading to their placement in yards to keep away snakes. This practice is based on anecdotal evidence, as regulatory bodies have never approved mothballs for repelling any of these animals.
The use of mothballs against these non-target species is generally unsuccessful because the toxic fumes dissipate too rapidly in open air to reach a truly repellent concentration. Animals that have established a den or a consistent food source will often tolerate the odor rather than abandon the location. Furthermore, a strong odor alone does not constitute an effective method of pest control.
How Exposure to Mothballs Occurs
The core mechanism of a mothball is sublimation, where the solid chemical compound converts directly into a gas, creating the odor that people associate with the product. When mothballs are scattered outdoors or in semi-open spaces, this vapor quickly disperses into the atmosphere. The concentration of the toxic gas remains too low to effectively repel or harm the intended nuisance animal.
However, this dispersal still creates significant environmental and health hazards. The solid mothballs themselves are often left accessible to curious pets and wildlife who may ingest them, mistaking them for food or toys. Animals that come into direct contact with the solid product can also absorb the chemicals through their skin.
When used in gardens or under decks, rain and irrigation can cause the chemicals to leach into the soil and potentially contaminate groundwater. This environmental contamination is a direct result of using a pesticide in a manner not specified on the label.
Toxicity and Regulatory Restrictions
The active ingredients in mothballs, naphthalene and paradichlorobenzene, are highly toxic compounds that pose significant health risks upon exposure. Ingestion is particularly dangerous, especially for small children and pets, who can suffer serious harm from consuming even a single mothball. Naphthalene is known to cause the breakdown of red blood cells, a condition called hemolysis, which can lead to severe anemia and kidney damage.
Chronic exposure to the fumes, which can occur when mothballs are improperly used in living spaces, can also damage the liver and central nervous system. Children with a genetic condition called glucose-6-phosphate dehydrogenase (G6PD) deficiency are particularly susceptible to severe red blood cell destruction from naphthalene. Therefore, the very presence of the mothball odor indicates exposure to these hazardous chemicals.
Because mothballs are regulated pesticides, the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) makes it illegal to use them in any way that violates the instructions on the product label. Using mothballs to repel any animal not listed on the label, such as squirrels, mice, or snakes, is a violation of federal law. Proper animal control methods should always be sought instead of resorting to the illegal and dangerous practice of off-label mothball use.