Why Do Mice Chew Through Electrical Wires?

Mice are clever and wily little rodents. They wiggle through holes you can barely fit a pencil through and love to chew on electrical wires. “Wires are often hidden in the same areas where mice can hide,” says Shannon Harlow-Ellis, associate certified entomologist and technical services manager at Mosquito Joe pest control experts. That means behind walls, in your basement, attic and garage, and even inside electrical equipment.

I’ll never forget the night — it’s always at night — I had to crawl around on the sticky floor of a restaurant kitchen to clean out an electrical transformer. (I was an electrical apprentice, and we always got the “best” jobs.) It was mouse-ridden, and one poor guy had nibbled on a wire. I’m sorry to say he did not make it.

You may not have a big transformer in your home, but you do have electrical outlets, appliances, cars and other wire-filled, tucked-away places mice love. Here’s why mice chew on wires and what you can do about it.

Why Do Mice Chew?

A few reasons, but the first is necessity. “Mice chew to keep their teeth maintained, as they have continuously growing incisors,” Harlow-Ellis says. “They gnaw material to keep them sharp and at a manageable length.” Mice are rodents, and like all rodents, if mice don’t keep their teeth short and sharp, their incisors get so long they can grow into the palate, leading to death by infection or starvation.

Mice also chew to gather nesting material and when in search of food, Harlow-Ellis says. A mouse traveling through your walls may come upon a barrier that it needs to get past, or something delicious to eat. Mice and other rodents are primarily herbivores, but they’re not too discriminating, as the piles of chewed-up insulation and drywall left in their wake can attest.

Why Do Mice Chew Electrical Wires?

Mice chew on electrical wires mainly because of their proximity. They hide and nest where electrical wires are likely to be, such as in attics and inside walls. They are curious and constantly on the lookout for food, shelter and things to gnaw on. Harlow-Ellis says it could also be a texture issue. Copper wires and the insulation covering them are soft and easy to chew.

Your car also has electrical wires, especially today’s high-tech models. And because your car is outside or in the garage, it’s easily accessible to mice, with lots of nooks and crannies for mice to hide. (Last week, I was stopped in traffic, and a mouse actually dropped from the car in front of me, ran around for a second on the pavement, and climbed back up the wheel well. It was nuts.)

If you’ve heard that mice like cars because auto manufacturers now use soy-based insulation, aka bioplastics, evidence is mixed. A peer-reviewed study published in the American Chemical Society’s Sustainable Chemistry & Engineering showed that mice did not favor soy-based products when exposed to both soy and traditional materials. Counterpoint: The study was financed by the United Soybean Board. Automakers like Toyota and Honda have been the subject of class action lawsuits over the issue, but litigation is ongoing (Toyota) or dismissed (Honda).

What Damage Can Mice Cause?

When it comes to damage mice chewing on wires can cause, the biggest one is fires. The poor dead mouse I found in the electrical transformer didn’t cause a fire because transformers are contained in a metal box. But it could be a different story if a mouse gets a hold of the wires in your wall. Damaged electrical wires cause arcing, or abnormal electrical discharges, that could easily ignite combustible materials in your wall.

In addition to electrical safety hazards, mice leave droppings everywhere they go, potentially contaminating food, bedding and furniture with bacteria and parasites. Gnawed-on wood framing members, drywall and insulation could lead to structural damage that could cost you big bucks to replace.

How To Prevent Mice From Chewing on Electrical Wires

From an electrical standpoint, metal electrical boxes and conduits for wiring are a nearly foolproof way to keep mice away. Mice are strong chewers, but they’re no match for a steel box or pipe with no access holes (unlike my transformer). Unfortunately, metal raceways are not common in residential construction. Most of the time, houses have plastic or PVC electrical boxes and a sheathed cable called Romex.

That’s why Harlow-Ellis says the best way to prevent mice from chewing on your wires is to prevent them from getting into your home in the first place. “Seal any cracks and holes in walls, floors and foundations of the home,” Harlow-Ellis says, and “use mouse deterrents like traps and powders at entry points.” Park your (clean, food-free) car in a garage if possible, and seal any openings that are a quarter-inch or larger. Keep dog food and birdseed tightly covered, and don’t store your garbage cans inside.

“For suspected infestations, consult a professional pest control company to help mitigate the issue,” Harlow-Ellis says.

About the Expert

Shannon Harlow-Ellis is an associate certified entomologist and technical services manager at Mosquito Joe pest control experts. A lifelong bug enthusiast, Harlow-Ellis is also the vice president of the Virginia Pest Management Association.

Sources

• American Chemical Society: Sustainable Chemistry & Engineering (2020). Assessing Rodent Gnawing of Elastomers Containing Soybean Oil Derivatives
• FindLaw: Heber v. Toyota Motor Sales, Inc. (2020)
• FindLaw: Caracci v. American Honda Motor Company (2024)