House Mouse Scat and Tracks: How to Identify Them (Mus musculus)

Rodent droppings are small and dark; shape and size are the first cut (rice-grain with pointed ends for mice, blunt and larger for rats, oval pellets for squirrels and voles). Tracks show four toes on the front foot and five on the hind, and most rodents bound, so the larger hind prints land ahead of the front prints. Gnaw marks with paired incisor grooves are often the clearest sign. The measurements below for House Mouse are quoted from the wildlife agencies linked at the bottom of the page.

• Size: About 0.25 inches long (same description as Deer Mouse droppings; the source page does not break this out by species)
• Shape: Slender, tapered at both ends

Norway Rat droppings are larger, about 0.5-0.75 inches long with blunt, rounded ends, unlike the House Mouse's slender droppings that taper at both ends The Deer Mouse page has its own sign list.

Human contact with the urine, droppings, and saliva of mice (including House Mice) can spread hantavirus If you need to clean it up, wear gloves and a mask, wet it down first, and bag it; see the CDC guidance linked in the sources.

Put something of known size next to it (a coin, a pen, a boot) and shoot straight down in soft light; low side light brings out the shape of tracks in mud or snow. For scat, photograph the whole deposit and one close-up showing contents. Note where it was: on a log, in the open, on a trail, near water. The app suggests the likely animal; confirm with the size and shape notes above.