How rats and mice get indoors is always a mystery. The belief is that a rat can enter through an opening the size of a nickel and a mouse through the size of a dime. But what they actually do is expand these size openings into access holes.
Creating passable openings from “nickels and dimes” is not difficult. Rodents can — and do — gnaw almost anything they can get their front teeth around. Rats attack material with a hardness of 3.5 or less on the Mohs scale of mineral hardness (Editor’s Note: For a chart and explanation of this scale, please visit NPS.gov). This gives them a wide range of possibilities, such as aluminum, lead, copper, asphalt, wood, sheetrock, plastic and soft mortar.
Commensal rodents’ jaws can bite with about 1-pound pressure, and they take 1.5 bites per second when they are intent on getting in. With this amount of pressure and diligence, they can turn “nickels and dimes” into easy entryways.