How to deter rodents from nesting in your car
I recently had an issue with at least one squirrel building a nest in my car's undercarriage. After several worrying lights on my dashboard decided to rear their ugly heads as a result of the infestation, I've been forced to do some homework while waiting for my car to return from the shop.
As this information is likely to be helpful to more than just me and more than just in this specific instance (it's definitely vanlife-adjacent), it seemed absolutely worthwhile to collate the information I've gathered from my research and share it with y'all.
And as this is one of my longer and more info-dense posts, y'all get a table of contents with section links.
Contents
What attracts them
Food, darkness, perceived permanence, shelter from threats, enclosed spaces...How to deter them
Lights
Lights are alright when it comes to deterrents for rodents. They're more useful when it's a novelty, a change in the environment, or something that is paired with another deterrent. On their own, a sensor driven light is something they'll grow accustomed to over time, because the light turning on at their motion doesn't have any other penalties associated with it.And they're not photosensitive... though it might ruin their night vision for a bit and make them more susceptible or visible to predators.
Also, lights can be a pain to set up. Either they need to be wired into a power supply, they have one built in (which periodically needs to be recharged), or they come with a solar panel built in (though these panels tend to run cheap, are prone to degrading when subjected to weather, and don't charge well when the sun is in any way obstructed).
Sounds
Ultrasonic devices
I've found a few recommendations for ultrasonic devices that claim to deter rodents. But they also claim they have no effect on cats (which seems more than a little suspicious). Most of the products come with mixed or poor reviews (when they have any at all). And as with lights above, rodents can grow accustomed to the sound if there's no penalties for ignoring it.They also have the same power supply problems as with lights. They either need to be plugged in, have batteries that need to be recharged or replaced regularly, or have built-in solar panels that come with a host of issues.
Ultrasonic devices also seem to run a little more expensive than non-ultrasonic deterrent devices on the market, which considering their efficacy seems to be borderline placebic, is more deterrent for humans than rodents.
Human activity
Human activity is a major deterrent for small, timid, prey animals, but those sounds alone are not sufficient. There's a whole host of regular pedestrians (often leaden with a dog or two) who pass by my car, and yet that alone was not enough to deter a squirrel from nesting in my car's undercarriage.As with everything else covered so far, the deterrent needs to be accompanied with consequences for ignoring it. The car needs to move, be interacted with, turned on, relocated, disappear on the regular for an hour or two...
Smells
Essential oils
All creatures with sensitive noses abhor strong smells. Even humans. My family uses citrus and peppermint oils to deter our cats from chewing on the Christmas decorations and clawing up the furniture. It works for a time, but it needs to be refreshed regularly to continue working.This is one of the few things on this list which needs no consequences. The burning in the nose when it's overloaded by the concentrated smell is the consequence. Even my eyes will start burning if I take too deep a breath or spill some on my fingers or clothes while handling it.
The tradeoff is that the smell degrades over time, even without the aid of weather (as any car parked consistently outdoors like mine is subjected to), and needs to be constantly refreshed.
Animal smells
This actually didn't come up in my generic searching for rodent deterrents, I had to ask the right questions to find it.My family keeps cats.
Cats are predators.
Our cats are indoor cats... but the local fauna doesn't know that.
Used litter, dander and tufts of hair, marking scents...
They'll all work as rodent deterrents.
We don't have bears in the area (we do have coyotes though), but I could probably go out and buy bear scent stuff from a hunting store and use that. (With the caveats, again, of regularly refreshing it and establishing consequences.)
Chemical repellents
Yes, you can buy bags to put in your car or garage to deter rodents that are less one specific scent and more of a chemical makeup of a bunch of different things to repel rodents. But of all the Smell-things discussed so far, these are likely the most expensive item on the list.And also like all the other Smells on the list, they only work for so long before you need to buy more.
Movement
I'm currently working two days on, then twelve days off. Simply driving my car more regularly (even when I don't actually need to go anywhere) is itself a deterrent.Now, my fuel consumption and general wear on my car will also go up, but those cost less than getting my car de-nested on the regular, and also probably less than some of the deterrents I've already mentioned.
Conclusion
Leaving my car alone for twelve days straight needs to stop, even if I don't need to go anywhere.Used cat litter will work as a suitable external deterrent (especially since my family literally pays to dispose of the stuff after our cats are done with it). Also, it can double as traction additives while this winter continues to linger.
I can put tufts of animal hair on the inside of the car, as long as I make sure not to give anyone a ride who might be allergic. And follow it up with some essential oils (though I have to carefully moderate them if I don't want to accidentally repel myself from my own car).
