Rodents
How big is a rat hole?
A young Norway rat can use a gap about ½ inch (think a US quarter as the teaching size). A House mouse uses about ¼ inch (a pencil). If you are stuffing steel wool in pinholes and still hearing heavy thumps, you do not have a mouse, or you missed the real opening.
The hole you see is not always the hole they use
Rats gnaw to enlarge a gap. A ⅜-inch utility hole becomes a door. Foam without a metal core is a snack. Use copper mesh or hardware cloth, then mortar, sheet metal, or a door sweep. CDC and EPA both put exclusion next to sanitation, not after a month of bait.
Burrow openings in soil are larger — a few inches across, with a smooth lip on an active Norway hole. That is a nest entrance, not the ½-inch building gap.
Species pages
The question is only the field note. Control sequence, legal notes, and identification live on the species article.
Norway rat
Rattus norvegicus
The Norway rat is the heavy, ground-dwelling commensal rat of US cities. It does not “decide” to live in…
House mouse
Mus musculus
House mice succeed because they need almost no water beyond the moisture in food, they fit through a 6 mm…
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