Why do pack rats chew car wires, and how do I stop it?

Arizona context

Pack rats turn up across the Gila Valley, Sierra Vista and the White Mountains. University of Arizona Extension says woodrats are most common in pinyon-juniper, chaparral and desert scrub country. The Internet Center for Wildlife Damage Management says they can be a nuisance around cabins, outbuildings and seldom-used vehicles, and may take up residence in parked vehicles, gnawing on wires and other mechanical parts.

Keeping pack rats out of your car

• Drive parked vehicles regularly and look under the hood when one has been sitting
• Keep all food out of the car
• If you use a car cover, use a weighted one that touches the ground all the way around
• Before starting a vehicle that has sat idle, air it out and check the air intake and filter
• Never sweep or vacuum a nest: wear gloves and soak it with disinfectant first
• Seal gaps in nearby garages and sheds, and clear nests close to where you park

Why pack rats go after car wiring

It starts with shelter. University of Arizona Extension says pack rats build nests in attics, garages, under houses and in the engine compartments of seldom-driven cars. The CDC says rodents may nest in cars, trucks, campers and other vehicles, especially ones that are used infrequently.

Then they chew. UA Extension says woodrats like to gnaw on the vinyl or plastic shielding of electrical wires and are notorious for chewing the wiring of cars and appliances. University of California IPM says rats commonly gnaw the insulating sheaths of engine wires, which can lead to significant malfunctions and costly repairs, and can do the same to trucks, tractors and farm equipment.

How to stop it

Use the vehicle, and look under the hood. The CDC says to air out a vehicle that has been idle for an extended period and inspect the air intakes and filters before starting the engine. It also says not to leave any kind of food in the car, and that rodents can get into the passenger compartment through ducting, rusted areas and cable conduit.

If you cover it, do it right. University of California IPM suggests a weighted car cover to keep rodents away from the engine and wires, but says it only works if the cover touches the ground and forms a seal all the way around the vehicle. UC IPM adds that rodent management around the yard and neighborhood will likely be needed for longer-term relief.

Deal with the pack rats nearby. UA Extension says exclusion and barriers are the most effective methods when woodrats are getting into structures, and that trapping by itself is not a long-term solution, so remove attractants and nests close to buildings. The CDC says snap traps and poison baits are effective at stopping rodents from getting into vehicles. If you use bait, UC IPM says all rodenticides are toxic to pets and people, so read and follow the label and keep them away from children and pets.

Skip mothballs. The Internet Center for Wildlife Damage Management says no woodrat repellents are registered by the EPA and chemical repellents are not considered a practical solution. The National Pesticide Information Center (NPIC) says mothballs are not wildlife repellents and that using them in a way the label doesn't specify is illegal.

Cleaning a nest out of a vehicle

Treat a nest as a health hazard. UA Extension says hantavirus and other diseases can be present in woodrat nests, and the CDC says the virus can get into the air when fresh urine, droppings or nesting materials from an infected rodent are stirred up. Don't sweep or vacuum it.

The CDC says to work in a well-ventilated space, open the hood, doors and trunk for 20 minutes, and remove the battery cables before inspecting the engine compartment. Wear plastic gloves and a long-sleeved shirt, spray the nest and droppings with disinfectant until fully soaked, let it sit for 5 minutes or as the label says, and pick it up with paper towels. If nesting material is in the air intake, remove it and replace the air filter. For chewed wiring, the CDC suggests a qualified mechanic or automotive professional.

When professional service is warranted

Get help if you keep finding nests or chewed wires, or if pack rats are getting into your garage, shed or home. University of Arizona Extension says exclusion and barriers work best when woodrats are entering structures, and that trapping by itself is not a long-term solution. For damaged wiring, the CDC suggests a qualified mechanic or automotive professional. If you get sick after cleaning up after rodents, the CDC says to talk to a healthcare provider and tell them about the rodent exposure. You can also call Poison Control at 1-800-222-1222 with questions. This is general information, not medical advice.

How Hydra handles it

We don't repair vehicles, but our Service Pros handle the pack rats around them in the Gila Valley, Sierra Vista and the White Mountains: removing nests near structures, sealing entry points in homes, garages and outbuildings, and setting up trapping and monitoring. Call or text your local office to reach an Office Pro, or ask for a free custom quote.

Frequently asked

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Related questions

• Are pack rats common in Arizona?
• How do I keep pack rats away from my property?
• Do peppermint oil, mothballs or ultrasonic repellers keep mice away?

References

• University of Arizona Cooperative Extension: Woodrats (Packrats), Backyard Gardener #23
• University of California IPM: Rats Pest Note
• CDC: How to Clean Up After Rodents
• CDC: Hantavirus Prevention
• Internet Center for Wildlife Damage Management: Woodrat Damage Identification
• Internet Center for Wildlife Damage Management: Woodrat Damage Prevention and Control Methods
• National Pesticide Information Center: Regulation, Proper Uses, and Alternatives of Mothballs
• 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)