Why do rodents chew wires?

I have found that chewed cables tend to be the ones that were not properly strapped along solid supports. It’s widely reported that rodent’s teeth never stop growing, and therefore require constant grinding to keep them from growing long enough to ‘hamper the hamster’. But why do they chew wires that could kill them?

I recall a recently published article suggesting that rodents chew because evolution selected for ‘neurotic’ traits that helped ensure the rodents have no difficulty with the will to keep their teeth properly ground down to size. Perhaps for parallel reasons of natural selection for reproduction, many of us don’t have sex to make babies (necessarily): we obsess about it and we enjoy it. It seems likely that rodents don’t chew to grind their teeth. They may enjoy chewing, it may be a neurotic itch or symptom, and it may be both. Whatever may be in the rodent’s brain, the result is that their teeth stay short enough that they can function.

On any given length of chewed wires, the most heavily-chewed portions are always the ones hanging in mid air — right at mouth height for everyone’s favorite furry rodent. Picture a neurotic character, your rodent, pacing up and down the length of a dark, dusty attic on a cold, windy night. Which cable are they going to get involved with? The one they trip over, over and over again, or the one their distracted consciousness probably doesn’t even register, because it’s neatly strapped to the building’s structural members?

In new construction, the National Electrical Code (NEC) requires that all cables be fastened snugly along solid supports where possible. In retrofit wiring, cables fished behind finished surfaces cannot be secured, so older homes will tend to have wiring that is more vulnerable to rodent chew.

That’s a good reason to keep an eye out for rodents and get rid of ones you do find, since someone went to trouble and expense to get good cable where it is, and you want to avoid having to do it again (not to mention the risk of welding a hole in a copper pipe or starting a fire — see also, AFCI).

Stop rodents: end chewed wires

No one wants to find a half-dead large rodent in a kill trap, but Philadelphians have an excellent alternative, in the live animal traps available free for borrowing (‘rental’) with $20 one-year membership, from West Philly Tool Library. You may still want to kill the rodent (it may come back if you set it free, and it will almost certainly bother someone if you set it free in an urban or suburban area, such as your local park), but with a live trap you can make the kill on your own terms rather than have to address a maimed rodent or rotting carcass in tight, dark spaces. For mice, the smaller tilt-to-shut live traps are a good bet — IF you are mindful about checking them daily and remember where you set them. Otherwise, the highly confined space inside may kill the mouse, and will result in a urine-soaked, tortured little fur-ball, if it doesn’t kill them.

While you’re watching for rodents, watch out for loose cable runs, especially in attics and utility spaces where installers may have let their standards for neatness and Code compliance slip. Consider hiring an electrician to properly secure cables, re-routing them where necessary, in order to minimize sections raised offset from the structure along which the cables run.

Note that loose cables are vulnerable to inattentive storage of heavy objects by humans, as well as chewing by rodents. If it’s an option for you as a new homeowner, try to have your wiring cleaned up before you store things against or on top of it (and in the way of workers). Human-pinched cables are a major statistical contributor among electrically-ignited house fires.

1 Comment

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  Robert Monk 2012/01/31 at 8:49 AM

  I heard you can discourage squirrel-chew in especially prone areas by rubbing cayan-pepper solution on the cables (or anything you don’t want chewed).

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