Q. We keep a mouse trap in our garage at all times because of ongoing problems with house mice getting into the garage. This time the mouse we caught looks different. It’s more brown and white and seems to have a larger head and longer tail than the mice we usually catch. Is this just a normal variation or did we catch some different animal?

A. I think your “guest” is probably a deer mouse. Deer mice are cute (at least to some people), but they can be hazardous to your health in certain situations. And cute or not, most people don’t want them in their house.

The deer mouse, Peromyscus maniculatus, is closely related to the white-footed mouse but is in a completely different mouse family than the house mouse. The deer mouse and the house mouse are roughly the same size, but most people think the deer mouse is “cuter” with its large eyes and ears, and its two-tone fur. It gets its name because its coloration resembles that of a white-tailed deer – tawny brown above and white below on the belly.

The deer mouse is involved with two diseases that affect people – Lyme disease and hantavirus. Although the white-footed mouse is the mouse most commonly associated with Lyme disease, the deer mouse can also carry the disease. It’s the blacklegged tick that actually transmits the disease to people when it feeds, but the mice act as reservoirs for the disease because the ticks also feed on them.

Hantavirus is much more common in western states but has been known to occur in the Northeast. The virus is found in the saliva, urine, and feces of the deer mouse and is spread to humans mostly when airborne virus particles are inhaled. You shouldn’t be worried about hantavirus with just one or two deer mice in your home, but you should avoid sites (like unused, outdoor sheds) that have large populations of deer mice with dusty accumulations of droppings and urine that can become airborne when disturbed.

The deer mouse is more common outdoors in rural or semi-rural areas but it can, and does, enter homes, especially in the fall. Deer mice are good climbers and can gain entrance to buildings by using trees, shrubs, and vines to get into attics or upper levels.

You know that at least one deer mouse got as far as your garage. There may be more. Some indoor nest sites favored by deer mice are drawers and storage cabinets in garages and sheds, attics if there are trees touching the roof, boxes and furniture stored in attics, and corner sill plates in basements or crawls. An indoor deer mouse nest can be over a foot in diameter and is lined with shredded paper, insulation, strips of cloth, or furniture stuffing. Deer mice urinate and defecate directly into their nests, and when the nest becomes too foul, the female just moves on and builds a new nest nearby!

Deer mice are also known for caching or hiding large amounts of food in out-of-the-way places. You may find deer mouse caches of seeds and nuts in wall voids, dresser drawers, cabinet voids, and other hidden places. Sometimes this stored food attracts insects, like the Indianmeal moth, that feed on stored food products. These insect infestations can then move into kitchen and pantry cabinets.

Give Colonial a call. We can inspect for deer mice (and house mice) and can set up a rodent management program so that you can get rid of those traps in your garage. An important part of rodent management is rodentproofing which means sealing all of those little openings that mice can use to get into your house. One common entry point for mice is under and around the garage door. Our experts can fix that, can seal or block other openings, and can advise you on other ways to keep mice out.