# Deer mouse

*Peromyscus maniculatus*

**Identification confidence:** Identifiable with care — The sharply bicoloured tail and white underside are reliable field features, and this identification matters because of hantavirus.


## How to recognise it

- Sharply two-toned colouring — brown to greyish above with a crisply white belly, feet, and underside, with a clean dividing line rather than a gradual blend.
- The tail is distinctly bicoloured, dark above and white below, which the house mouse's uniformly greyish tail is not.
- Eyes are large and prominent, and ears are large and thinly furred.
- The body measures 70 to 100 mm excluding the tail, making it slightly larger and longer-legged than a house mouse seen alongside it.

## What it leaves behind

- Nests of shredded plant material in outbuildings, cabins, sheds, vehicles, and stored equipment.
- Caches of seeds and nuts in enclosed spaces.
- Droppings similar in size to house mouse droppings and not reliably distinguishable by eye.

## Why an infestation persists

Deer mice are the primary reservoir of Sin Nombre hantavirus in North America, which causes hantavirus pulmonary syndrome. Infection risk is associated with breathing dust from disturbed nests, droppings, and urine in enclosed spaces — cabins, sheds, crawl spaces, and stored vehicles that have been closed up. That is the entire reason this identification matters to a homeowner, and it changes how a contaminated space should be handled: ventilate before entering and do not dry-sweep or vacuum the material.


## Where it occurs

Across most of the United States, predominantly in rural, wooded, and grassland settings rather than dense urban areas.

## What prevents it

- Ventilate closed outbuildings and cabins for at least 30 minutes before entering and cleaning.
- Never dry-sweep or vacuum rodent droppings or nests; consult CDC guidance on wetting the material before removal.
- Exclude with the same 6 mm standard used for house mice.
- Keep stored feed and seed in sealed rigid containers and clear brush away from outbuildings.

## Commonly confused with

- **House mouse** (*Mus musculus*) — Droppings are 3 to 6 mm, rod-shaped with pointed ends, and scattered widely rather than deposited in one place — a single mouse produces dozens per day.

**Verdict:** professional-recommended. Hantavirus risk makes cleanup of a contaminated enclosed space a health matter rather than a housekeeping one. Follow CDC guidance, and get help for a heavily contaminated building.


Source: https://againstpest.shop/identify/rodents/deer-mouse/