House Mouse

The house mouse is usually dusky gray with a semi-naked tail

The house mouse (Mus musculus) which infers ‘little thief’ is the most common of the numerous types of mice that we may encounter in our homes and businesses.The house mouse is usually dusky gray with a semi-naked tail which is about as long as the body and has large ears. They are 8 to 9 cm long and weigh up to 21 grams when fully grown.These mice as with many of our pest species are not native to North America but were brought over on the early sailing ships. They are distinct from other rodents such as pine, deer and meadow mice and rats.

Female mice will reach sexual maturity at about one and one half months and can produce and average of 5 to 8 young per litter. Since their gestation period is about 20 days, they are capable of producing 30 to 40 young per year. This is why house mouse populations can become so high if they are not controlled. I have encountered populations well into the several thousands in seed warehouses and certain types of agricultural operations. In homes it is often just a matter of a few mice but numbers into the dozens will occur if they are not controlled. Mice will generally live for about a year.

Mice are omnivores and will eat a variety of foods, but are nibblers and eat only small amounts at any one time consuming about 10 to 15 percent of their body weight per day. They will drink water frequently but can live without it if they have to. If they have sufficient food and shelter, they can live within a very small area and will not leave that area.

Mouse Facts

  • Their droppings are black, thin, usually pointed and up to about 60 mm long. They can be the colour of their food source and mice that have been feeding on green or pink rodenticides will often have green or pink droppings.
  • Mice can fit through an opening as small as 1 ½ cm or squeeze under a door with a 1 cm gap.
  • One pair of mice can deposit 18,000 droppings in six months.
  • Mice urinate continuously as they run contaminating food and surfaces as they pass over it.
  • Mice are associated with several human diseases including salmonellosis, rickettsialpox, histoplasmosis, tularemia and others.
  • Mice and rats can live in the same structure but in different territories.
  • Mice prefer foods such as gumdrops, peanut butter or prunes (cheese is down the list).


Mice can enter a home in numerous ways, but attached garages and attics are the most common. The weather stripping on the bottom of garage doors often is not tight enough to prevent mice from entering. Storage of birdseed, pet foods or garbage if not kept in tight containers is an open invitation. Mice are able to climb up any rough surface and readily go up the outside walls of homes and then enter any gaps between the wall and soffits and gain access to the attic. Once in the attic they can make their way down through the walls and into the house.

Sealing obvious gaps and openings should be the first line of defense. Traps such as snap traps, small live traps and multiple catch traps such as Ketch-all traps are all effective trapping devices. Rodenticides containing brodifacoum or bromadiolone are effective but care must be used when children or dogs are present. Despite the perception that dogs must eat large quantities to be affected, I have found that very small amounts of these materials can be toxic to dogs. Cats generally will not eat rodenticides but may consume poisoned mice.

Fall is the time when rodents are looking for a winter shelter and our homes are ‘Florida’ to mice so start your prevention program now.