Do Mothballs Or Ultrasonic Repellers Keep Mice Out?

Mothballs and ultrasonic plug-ins do not keep mice out of an Ohio house. Mothballs are a registered pesticide whose label allows one use site, a closed container, so an attic or crawlspace is an off label use. Ultrasonic devices carry a long record of federal advertising complaints rather than field results. Closing openings and trapping is what changes the outcome.

October is when the question comes up. Nights cool off, something turns up behind the dryer, and the shelf at the hardware store offers a bag of mothballs next to a plug-in that promises an empty house. Both look easier than pulling a section of siding. In one case, what the product is allowed to do is printed on the box.

Are Mothballs Legal To Use For Mice?

Not outside a closed container. Mothballs are pesticide products registered with the EPA, and a pesticide label is enforceable: the use site printed on it is the only place the product may legally go. The National Pesticide Information Center, a cooperative program of Oregon State University and the EPA, states that registered mothball products name air tight containers and storage closets as their use site, and that using them in a way the label does not specify is illegal.

The EPA uses an example in its pesticide labeling questions and answers: putting mothballs on the grass along a fence line to repel cats would be unlawful, because the label names air tight containers and storage closets as the use site and a fence line is not one of them. An attic floor, a crawlspace, a wall void and a flower bed all fail the same test. NPIC adds the other half of it, that mothballs are registered to kill clothes moths and carpet beetles inside enclosed containers and are not meant to be used as animal repellents at all.

Ohio enforces federal pesticide law through the Ohio Department of Agriculture, so none of this stops at the state line. Our guide to what pet safe pest control actually means has the longer version of how those labels are written.

What A Mothball Actually Does In An Attic

It evaporates. The active ingredient leaves the solid as a vapor, and the vapor is the pesticide. NPIC puts it in one line: when you smell mothballs, you are inhaling the pesticide. The label calls for a tightly closed container so those fumes build up where the clothes moths are instead of in living space. An attic is the opposite of that container.

What a mouse or a squirrel notices in an open space is odor, and odor only deters a mammal at a concentration an open space will not hold. The Internet Center for Wildlife Damage Management, a clearinghouse for published wildlife damage research, says mothballs do annoy mammals but that high concentrations of the odor are needed for it. A handful scattered across attic insulation never gets close.

The exposure, meanwhile, is real. NPIC reports headaches, nausea, dizziness and vomiting in people exposed to naphthalene vapors, and that breathing in enough of it, or eating a mothball, can cause hemolytic anemia, in which red blood cells break apart and stop carrying oxygen properly. Children and pets are at particular risk because mothballs look like candy, and clothing stored with mothballs and then worn unwashed has caused anemia in infants. Paradichlorobenzene, the other common active ingredient, has its own NPIC list: nausea, vomiting, dizziness, fatigue, headaches and irritation of the eyes and nose. A product that does nothing to the mouse can still reach the people under the attic hatch.

Where Each Fall Favorite Stands

Three of the rows below are products. The fourth is the work those products get bought to avoid.

Do Ultrasonic Plug-Ins Repel Mice?

The agency that has looked hardest at that question is the Federal Trade Commission, and it was looking at the advertising. Between 1985 and 1997 the FTC brought law enforcement actions against six companies over false and unsubstantiated claims that ultrasonic devices controlled rodent and insect infestations. In May 2001 it sent warning letters to more than 60 manufacturers and retailers of these devices, telling them that efficacy claims had to be supported by scientific evidence. More cases followed in 2002 and 2004.

The reasoning in those complaints matters more than the dates. The FTC alleged that any reaction by rodents to ultrasound would be temporary at best, because rodents become accustomed to the sound and return to their nesting and feeding areas with the device still running. It also alleged that the devices do not control insects at all, which is the other half of what the boxes tend to promise.

Extension sources land in the same place. The Internet Center for Wildlife Damage Management says there is little evidence that ultrasonic devices are effective, and the University of California statewide IPM program lists ultrasonic and electromagnetic devices among the methods that do not work on voles. A mouse already living in a wall has somewhere to be, and sound does not take that away.

What About Peppermint Oil And Natural Repellents?

Most of the pouches and sprays sold for mice are built from ingredients on the EPA list of active ingredients allowed in minimum risk pesticide products, which includes peppermint oil along with cedar, citronella, clove, garlic, lemongrass, rosemary and thyme oils. Products made only from that list, under the conditions in the rule, are exempt from federal pesticide registration, an exemption the EPA created in 1996 to lower the regulatory burden on products posing little or no risk.

Packaging often turns that into a compliment. Exempt means the EPA did not review the product, not that the EPA cleared it as effective. Whether the bag in your pantry moves a mouse is a question nobody at the federal level examined, and a scent does not close the gap the mouse came through.

What To Do Instead Before The First Freeze

Ohio State University Extension treats exclusion as the first move: find the gaps outside and inside the space, caulk, repair or screen them, and once rodents are known to be present, seal the openings and trap, with snap traps the safest choice in a home. Mice use a gap about the width of a dime, so the openings worth finding rarely look dramatic.

• Walk the outside in daylight: door sweeps, garage seals, siding transitions, vents, and every place a pipe or cable passes through a wall.
• Use materials a mouse cannot chew. Sealant alone fails where hardware cloth or metal backing holds.
• Trap for what is already inside. An opening closed behind an active mouse solves half the problem.
• Put pantry goods, pet food and bird seed in closed containers and keep garbage shut.
• Clean up the signs you found, then check in a week so fresh droppings read as new activity.

For the room by room version of the first item, use our guide to mouse entry points in Ohio homes, and for how long the trapping half runs, see how long it takes to get rid of mice. When the activity is in a wall, an attic or more than one room, our residential rodent control service runs that sequence with an inspection in front of it, and the North Canton and Hartville pages describe how it applies to older local housing and to outbuildings.

State Termite has worked in Stark and Summit counties since 1933. If there are mothballs in your attic, or a plug-in in the hallway and droppings in the pantry anyway, call 330-494-6199 or request a free estimate and we will look at the building instead of the shelf.