Why do mice chew on wires and furniture?

A mouse's incisors are hypselodont — rootless, and growing continuously throughout its life, at roughly 0.4 millimeters a day. Without regular wear, the teeth would overgrow, curve into the mouth or jaw, and cause malocclusion, a painful misalignment that ultimately keeps the animal from eating and leads to starvation. Gnawing, in other words, isn't optional. It's the same biological maintenance every mouse performs regardless of whether food, shelter, or valuables are anywhere nearby.

For a long time, the working assumption was that gnawing was a purely mechanical behavior — teeth grow, so the animal chews. Research published in Neuron overturned that simple picture: a touch-guided neural circuit rewards gnawing with a dopamine release in the brain's reward center, and disrupting that circuit doesn't just reduce gnawing, it abolishes it and produces severe malocclusion. Activating the circuit, conversely, triggers the reward response directly. The study's lead author summarized the old view as treating gnawing as "a very passive behavior driven by mechanical considerations" — which the data show it plainly is not. Mice are motivated to gnaw, not just obligated to.

Both wires and furniture get chewed for the identical biological reason, but the consequences aren't remotely equal. A gnawed chair leg is cosmetic — unattractive, but structurally and functionally harmless. A gnawed wire is different: strip the insulation off an energized conductor and you have exposed metal capable of arcing, which is a recognized and physically real ignition pathway in fire investigation. That distinction — same behavior, very different stakes depending on the object — is the single most useful thing to take from this page.

It's common to see the biological explanation for mouse gnawing used as a springboard straight into the claim that rodents cause 20 to 25 percent of house fires. That specific number has no home in any fire authority's data: NFIRS, the federal database fire departments use to code causes, has no rodent or animal-specific ignition category, and NFPA's actual animal-related figure — pets and wildlife combined having a part in roughly 750 home fires a year — is a small fraction of what the popular claim implies. The honest position holds both truths at once: the gnawing is completely real, and exposed wire is a genuine hazard worth an electrician's attention, while the specific statistic used to dramatize it is invented.