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White-footed deermice moving indoors in autumn with their seed caches

October to November

White-footed deermice, the big-eyed woodland mice that spend summer in stone walls and oak leaf litter, move into houses, sheds and garages as the nights turn cold. They bring their autumn habit with them, so the first sign is almost never the mouse but its hoard: seeds or gnawed acorn shells tucked somewhere absurd.

Why this time of year

Two things land together in October and November. Cool weather sends these mice looking for a protected place to spend the winter, and it is also the season when seeds and nuts are most plentiful, which is when they cache. They do not hibernate, so a mouse that moves into the garage in October has to bank a winter's groceries there.

How to notice it

  1. Look where a mouse would treat a hollow tree as having better weather: the toe of a boot in the mudroom, a coat pocket in the shed, a boat cushion, a rolled sleeping bag, the back of a workbench drawer. You want a deliberate pile of seeds, acorn pieces or kibble nobody put there.
  2. Look at what was opened. Collect a few gnawed shells from the cache with gloves, then pick up a few acorns opened outside under the oaks and line them up. Working out which animal opened which is the activity.
  3. Check for droppings along the back edges of shelves rather than in one pile. Wear gloves and read the safety notes before touching or clearing anything.
  4. After dark, sit still in a quiet room or the garage and listen at the skirting boards. These mice are nocturnal, so scratching in a wall after the house goes quiet is likely them.

Try this with kids: Count the seeds in the cache before anybody clears it. A mouse carries them roughly one at a time, so that is also the number of trips it made in the dark.

a white-footed deermouse does not hibernate, so it has to store food it can reach in February

Safety

  • You cannot catch Lyme disease from a mouse. It is spread by the bites of infected ticks, and a tick generally has to be attached for more than 24 hours. Mice matter to Lyme because young ticks feed on them outdoors, not because a mouse in the shed can pass it to you.
  • Some rodent droppings can carry hantavirus, and in this state the risk is very small: the Massachusetts Department of Public Health says human hantavirus infections are extremely rare in Massachusetts and throughout New England.
  • Use the cleanup method the agencies recommend anyway, because it costs nothing. Do not sweep or vacuum droppings or nests, which puts dust in the air. Wear rubber or plastic gloves, wet the area thoroughly with disinfectant or a bleach and water mix, leave it five minutes, wipe with paper towel, then mop. Wash hands before and after removing the gloves.
  • Treat a cache the same way: look at it, count it, photograph it, then clear it damp and gloved. Do not let children handle cached seeds bare-handed.
  • Do not pick up a mouse, alive or dead, with bare hands.
  • If you would rather they were not indoors, the fix agencies recommend is exclusion rather than killing: seal openings larger than a quarter of an inch, especially at the foundation and where pipes enter.

Sources

  • mass.govMassWildlife mammal list: the White-footed Deermouse is statewide in Massachusetts, while the North American Deermouse is known with certainty only from Berkshire, Franklin and Hampshire counties and specimens outside that range need verification. This is why the card names one species.
  • cals.cornell.eduCornell IPM: white-footed mice and deer mice spend most of their time outdoors but ENTER STRUCTURES FROM FALL THROUGH SPRING, and finding them indoors means there is an opening they are using.
  • icwdm.orgInternet Center for Wildlife Damage Management, the correct source for the caching claim: white-footed and deer mice have a greater tendency to cache food supplies such as acorns, seeds or nuts than do house mice, and they tend to enter homes and other structures that are not rodent-proof.
  • mass.govMassachusetts Department of Public Health, and the sentence this card's reassurance now rests on: human infections of hantavirus are extremely rare in Massachusetts and throughout New England. Also the exact cleanup protocol reproduced in the safety notes, and the quarter-inch exclusion figure.
  • cdc.govCDC surveillance: 890 cases of hantavirus disease reported in the United States from the start of surveillance in 1993 through the end of 2023, with 94 percent occurring west of the Mississippi River. Note 890 is hantavirus DISEASE; the pulmonary-syndrome-only figure is 859.
  • cdc.govCDC: Lyme bacteria are spread to people through the bites of infected ticks, immature ticks become infected feeding on wildlife hosts usually rodents, and in most cases a tick must be attached more than 24 hours before transmission. This is the basis for the correction that a mouse indoors is not itself a Lyme exposure.
  • extension.unh.eduUNH Extension: the autumn trigger, that cooler fall weather sends mice looking for a protected place to spend the winter, plus the dropping description and the quarter-inch exclusion figure.
  • ipm.ucanr.eduUC IPM: these mice are nocturnal, do not hibernate but may become torpid in severe weather, often enter vacated structures where they build nests and store food, and the bicolored tail is the easiest feature separating them from house mice. NOTE this is a California page about Peromyscus maniculatus, so it is cited for general behaviour and NOT for the Massachusetts caching claim, which rests on icwdm.
  • caryinstitute.orgCary Institute, Richard Ostfeld's long-term research: acorn boom and bust cycles drive white-footed mouse numbers, and these mice are preferred hosts for black-legged ticks and effective transmitters. Background for the mouse-and-tick link only; its risk season is the May to July nymph peak, not autumn.

Checked against these sources on September 6, 2026.

In the guide for October, November

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