The Three Missouri Species
House Mouse
The house mouse (Mus musculus) is Missouri's most common structural rodent — small (2–4 inches body), gray-brown, with large ears and a nearly hairless tail. House mice are year-round indoor residents that establish nesting in wall voids, crawlspaces, attic insulation, and cabinet interiors. They enter through gaps as small as 1/4 inch — the diameter of a dime — and a single breeding pair can produce 50–60 offspring per year in a structure with adequate food and harborage.
Deer Mouse
The deer mouse (Peromyscus maniculatus) is distinguished from house mice by its bicolored tail (dark above, white below) and white underbelly. Deer mice are primarily outdoor-to-indoor migrants in fall as temperatures drop, most commonly entering rural properties, outbuildings, and homes adjacent to wooded or agricultural land. Deer mice are the primary hantavirus reservoir in Missouri — their droppings and urine carry hantavirus risk that house mice do not, making deer mouse infestations a more serious health concern that warrants professional handling.
Norway Rat
The Norway rat (Rattus norvegicus) is substantially larger — up to 10 inches body length — and primarily associated with urban commercial environments, sewer systems, and properties with consistent outdoor food sources (bird feeders, compost, unsecured garbage). Norway rats burrow and are more commonly encountered at foundation level than in attics. Their entry gaps need to be 1/2 inch or larger.
Common Mouse Entry Points — Inspect These First
- Gaps around utility penetrations — gas lines, electrical conduit, HVAC pipes through foundation or sill plate
- Weep holes in brick veneer — standard size allows mouse entry
- Door threshold gaps — a 1/4-inch light gap under a door is a mouse highway
- Crawlspace vent screens — deteriorated screens or missing screens on crawlspace vents
- Garage door bottom seal gaps and the door-to-frame gaps at corners
D&D Pest Control handles rodent exclusion and baiting programs for Franklin County and rural Missouri — visit ddpestcontrolmo.com.