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If you own a car, it’s a good idea to be on the lookout for mice that can find their way into the engine compartment, trunk or interior. That’s because as far as a mouse is concerned, a parked vehicle with all of its small internal spaces and compartments make perfect nesting spots. Things like air filters, vent ducts and trunks are dry and out of the wind, places to hide from predators and good places to store food.

The issues of having these tiny hitchhikers range from mildly annoying to dangerous depending on the damage they inflict on your vehicle. Here are five signs there are mice in your car.


If you turn your heater, defroster or air conditioner on and notice a rumble or vibration coming from the vents, a mouse is the likely culprit, according to Mark Roy, owner of M&M Service in Fort Kent.

“I have people come in and tell me when they turn their heater on they hear a rumble,” Roy said. “That means there is debris in the fan or the mouse has gotten caught in the fan.”


Another thing that will happen if you have mice in your car when you turn on any of the fan functions is debris blowing out of the vents. It could be small seeds, pieces of grass or straw. Roy said if that happens, look for mice. He also pointed out that newer model cars come equipped with cabin air filters that do a good job blocking that debris from entering the car through the vents. So it’s a good idea to look for debris behind or building up on those filters.

A foul smell

Mice are perfectly happy running not only running around inside your car, but using it as their bathroom. When enough mouse urine and droppings collect it’s going to produce a bad smell that will only get worse over time. The smell of fresh mouse urine has been described as an ammonia-like odor. Older, fermented urine starts to smell like damp wood. The droppings will have a much stronger ammonia smell.

Stored food

Mice love to store food and areas under the hood of your car or under the spare tire well in the trunk are perfect mouse larders and should be checked frequently if you suspect mice are around.

The air filters on your engine are also popular places for mice to store food. Roy said a mouse or family of mice can cram every nook and cranny of an air filter full of nuts, seeds or bird food. An air filter blocked by mouse activity can reduce your overall fuel economy and cause your car to misfire and idle roughly, among other things.

Chewed up items

Look for direct evidence of mice inside your car like chewed or shredded paper products, upholstery or carpeting. Mouse droppings or their tiny tracks on dusty dashboards are proof positive they are spending time in your car. Less immediately obvious, but important to look for are holes in your engine’s air filter. According to Roy, mice love to chew on those filters for some reason.

“If you see holes in your air filter, that’s 100 percent a mouse,” Roy said.

Of course, if you see an actual mouse scampering on the car’s floorboard or across the seats, you have 100 percent proof they are in your car.

“It’s pretty typical to see mice in a car this time of year,” Roy said. “I have seen some already but it does not seem to be worse this year than any other.”

You want them removed

For the most part, mice in a car are a smelly or messy nuisance, but Roy cautioned they can cause some real problems leading to mechanical or electrical failure in your car.

“For some reason they like to chew wires,” Roy said. “That can cause some real damage and that’s when the mouse goes from a cute little critter to not being funny anymore.”

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Julia Bayly

Julia Bayly is a reporter at the Bangor Daily News with a regular bi-weekly column. Julia has been a freelance travel writer/photographer since 2000.