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House Mice

Ways to recognize, control, and prevent mouse problems

The house mouse (Mus musculus) is considered one of the most troublesome and economically important rodents in Canada. They are found in and around homes and commercial buildings and thrive under a variety of conditions. House mice consume and contaminate food meant for humans and pets. They cause damage to structures and property by gnawing and leaving fecal pellets and urine and they are capable of spreading disease.

Droppings, fresh gnaw marks, and tracks indicate areas where mice are active. Mouse nests, made from fine shredded paper or other fibrous material, often are found in voids and other sheltered locations. House mice have a characteristic musky odor that identifies their presence. Mice are active mostly at night, but can be seen occasionally during daylight hours.

House mice are small rodents with relatively large ears and small black eyes. They weigh about 15 grams and usually are light gray in color. An adult is about 14 to 17 cm long, including the 6 to 8cm tail.

Although house mice usually feed on cereal grains and seeds, they will eat almost anything. They are sporadic feeders, nibbling tiny bits of food here and there. Mice have keen senses of hearing, smell, taste and touch. They are excellent climbers and can run up any rough vertical surface. They will run horizontally along wire cables or ropes and can jump up  30 cm from the floor onto a flat surface. Mice can squeeze through doors where there is more than a  6 mm gap and through holes the size of a dime.

In a single year, a female may have five to ten litters of usually six or eight young each. Young are born 19 to 21 days after mating, and they reach reproductive maturity in six to ten weeks. The life span of a mouse is usually nine to twelve months.

Effective control involves three aspects: sanitation, mouse-proof construction, and population reduction (poisoning ). The first two are preventive measures.

Proper sanitation is an important step in controlling house mouse populations. In particular, eliminate places where mice can find shelter. They cannot survive in large numbers if they have few places to rest, hide, or build nests and raise their young. Total elimination of mice through sanitation, however, is almost impossible. Mice can survive in small areas with limited amounts of food, moisture, and shelter. Most buildings where food is handled or stored will have problems with house mice, no matter how clean they are if they have not been "mouse-proofed." 

Mouse-proof construction is the most successful and permanent form of house mouse control. "Build them out" by eliminating all openings larger than 6 mm through which they can enter a structure. Steel wool or copper mesh may be stuffed into holes. Seal cracks in building foundations and openings for water pipes, vents, and utilities with metal or concrete. Doors, windows and screens should fit tightly. Cover the edges of doors and windows with metal to prevent gnawing. Latex, plastic, rubber, wood, spray foam, or other gnawable materials are unsuitable for plugging holes used by mice. 

Multiple-dose (anticoagulant) rodenticides - Multiple-dose anticoagulant rodenticides cause death as a result of internal bleeding, which occurs as the animal's blood loses the ability to clot and capillaries are damaged. The active ingredients are used at very low levels, so bait shyness does not occur when using properly formulated baits.

Mice often feed on anticoagulant baits for several days before death occurs. Fresh bait must be made available to mice   for at least two weeks, or as long as feeding occurs.

 Several types of anticoagulant baits are available.   Anticoagulant baits formed into paraffin blocks are useful in damp locations, crawl spaces, outside under porches, and other areas where loose grain baits spoil quickly.

Proper placement of baits is important for house mouse control. We place baits  in areas where mouse activity is evident. If mice are living in wall spaces, we place baits inside plumbing voids and pipe runs, above suspended ceilings, and in attics. 

Electronic devices - Although mice are easily frightened by strange or unfamiliar noises, they quickly become accustomed to regularly repeated sounds, usually after 12-24 hours. Ultrasonic sounds, those above the range of human hearing, have very limited use in rodent control because they are directional and do not penetrate behind objects. They also lose their intensity quickly with distance. There is no evidence that electronic, sound, magnetic, or vibrational devices of any kind will drive established mice or rats from buildings or provide adequate control.

Predators - Although cats, dogs, and other predators may kill mice, they do not provide effective mouse control in most circumstances. Mice often live in very close association with dogs and cats. Mouse problems around homes often are related to the food, water and shelter provided for the pet.

 Deer mouse 

The deer mouse is a small, white-footed mouse with large dark eyes and long whiskers. The soft fur of the deer mouse varies in color from a golden brown  to a  dark brown on the back, while the under-parts are white   Adult deer mice weigh from 10-35g. with external measurements averaging 170 mm for total length. 

Deer mice do not usually occur in urban areas.

 

The deer mouse is omnivorous, and feeds on seeds, plant greens, berries, nuts, mushrooms, insects and collecting seeds for winter. This habit makes more difficult to control them with poison baits, especially in the first half of the winter. 

Breeding starts very late in the winter and  on average, the deer mouse has about four litters each year. The gestation period  averaging about 24 days. Litter size  averaging about  six.     

 Hantavirus is a viral disease carried by wild rodents – especially deer mice, which in Canada are the principal animal reservoirs of the virus. The mice themselves don’t appear to get sick from the virus. 

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