Do peppermint oil, mothballs or ultrasonic repellers keep mice away?

Arizona context

These products get bought when mice move indoors as Arizona nights cool off, from Gila Valley homes to White Mountains cabins and Sierra Vista garages. University of California IPM says that where house mice live outdoors, they often enter homes in autumn when nighttime temperatures get colder. A cabin that sits empty all winter is exactly where a plug-in repeller or a box of mothballs can give you false confidence.

What to do instead of a repeller

• Seal gaps a mouse could fit through with wire screen or coarse steel wool
• Set snap traps near droppings, gnaw marks and other signs of activity
• Keep food storage and garbage containers sealed, and feed pets only what they'll eat at one feeding
• Use mothballs only as the label directs, in a closed, airtight container for clothing
• Don't sweep or vacuum droppings: spray them with disinfectant first

Ultrasonic plug-in repellers

University of California IPM says ultrasonic sound has very limited use in rodent control because it is directional, doesn't get behind objects and loses intensity quickly with distance. House mice are easily frightened by strange noises, but UC IPM says they quickly get used to sounds that repeat.

Testing backs that up. A USDA National Wildlife Research Center review of six commercial ultrasonic devices found only marginal effects and rapid habituation, with no significant repellency beyond 3 to 7 days, and concluded the devices did not have enough repellency to be useful for rodent control, whether used alone or with baits, traps or glue boards. The Internet Center for Wildlife Damage Management says commercial ultrasonic devices are not recommended as a solution to infestations.

Bugs are no different. University of Arizona Extension reviewed the research and says commercially available sonic pest devices for homes have not been shown to be effective in scientific studies, so it does not advise using them. Studies it cites found no effect on German cockroaches or bed bugs, devices failed to repel ants, and in one study devices sold to repel mosquitoes increased bite rates by as much as 50%.

Peppermint oil

The Internet Center for Wildlife Damage Management says natural oils, including mint oil, are sold as mouse repellents, but little information is available on how well they work. In a 2022 laboratory study published in Natural and Life Sciences Communications, peppermint oil repelled lab mice at first but showed no significant repellent effect after seven days. That was a lab test, not a house with mice already nesting in the walls.

University of California IPM says much the same about rats: they have an initial aversion to some odors and tastes, but no repellents have been found to solve a rat problem for more than a very short time.

Mothballs

Mothballs aren't a rodent product. The National Pesticide Information Center (NPIC) says mothballs are pesticides meant to kill clothes moths and other fabric pests, that they are not wildlife repellents, and that the label says exactly where and how they can legally be used. Using them in a way the label doesn't specify is illegal and can harm people, pets or the environment.

NPIC says mothballs used in the open can harm people, pets or wildlife that touch them, eat them or breathe the vapors, and should not be used around food or food preparation areas. It also says children often mistake mothballs for food when they're used improperly around the home.

What works instead

Keep mice out and trap the ones inside. University of California IPM says house mice can squeeze under gaps 1/4 inch tall and through openings 3/8 inch wide, and recommends sealing cracks and openings with wire screen or coarse steel wool that mice can't chew through. It calls snap traps a great first step and says trapping is the preferred method in homes, garages and other structures where only a few mice are present.

When professional service is warranted

Get help if you still see droppings, gnaw marks or mice after sealing and trapping, or if you can't find where they're getting in. University of California IPM says house mice tend to stay within 30 feet of their nest, so the source is usually close by. If a child may have swallowed or touched mothballs or another pesticide, call Poison Control at 1-800-222-1222. NPIC answers pesticide questions, including questions about pets, at 1-800-858-7378. This is general information, not medical advice.

How Hydra handles it

Our Service Pros find where mice are getting in, seal entry points, and set up trapping and monitoring in the Gila Valley, Sierra Vista and the White Mountains. To talk it through, call or text your local office to reach an Office Pro, or ask for a free custom quote.

Frequently asked

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• Will a cat keep mice away?
• How small a hole can a mouse or rat squeeze through?
• Do mice come back to the same cabin every winter?
• Why do pack rats chew car wires, and how do I stop it?

References

• University of California IPM: House Mouse Pest Note
• University of California IPM: Rats Pest Note
• Internet Center for Wildlife Damage Management: House Mouse Damage Prevention and Control Methods
• Shumake, S.A. (1997). Electronic Rodent Repellent Devices: A Review of Efficacy Test Protocols and Regulatory Actions. USDA National Wildlife Research Center
• University of Arizona Cooperative Extension: Sonic Pest Repellents (AZ1639)
• Chulikhit, Y. et al. (2022). The Repellent Potential of Herbal Oils Alone and in Combination in Mouse Behavioral Models. Natural and Life Sciences Communications (2022, No. 3)
• National Pesticide Information Center: Mothballs
• National Pesticide Information Center: Regulation, Proper Uses, and Alternatives of Mothballs
• National Pesticide Information Center: Pesticides and Children