The house mouse (Mus musculus) is considered one of the most troublesome and economically important pests in the United States. House mice live and thrive under a variety of conditions in and around homes and farms. House mice consume food meant for humans or pets. They contaminate food-preparation surfaces with their feces, which can contain the bacterium that causes food poisoning (salmonellosis). Their constant gnawing causes damage to structures and property.
Recognizing Mouse Infestations
Droppings, fresh gnawing and tracks indicate areas where mice are active. Mouse nests, made from fine shredded paper or other fibrous material, are often found in sheltered locations. House mice have a characteristic musky odor that identifies their presence. Mice are occasionally seen during daylight hours.
House Mouse Facts
House mice are gray or brown rodents with relatively large ears and small eyes. An adult weighs about 1/2 ounce and is about 5 1/2 to 7 1/2 inches long, including the 3 to 4 inch tail.
Although house mice usually feed on cereal grains, they will eat many kinds of food. They eat often, nibbling bits of food here and there. Mice have keen senses of taste, hearing, smell 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 13 inches from the floor onto a flat surface. They can slip through a crack that a pencil will fit into (sightly larger than 1/4 inch in diameter).
In a single year, a female may have five to 10 litters of usually five or six young each. Young are born 19 to 21 days after mating, and they are mature in six to 10 weeks. The life span of a mouse is about nine to 12 months.
Prevention and Control
Effective mouse control involves sanitation, mouse proof construction and population reduction. The first two are useful as preventive measures. When a mouse infestation already exists, some form of population reduction is almost always necessary. Reduction techniques include trapping and poisoning.
Sanitation. Mice can survive in very small areas with limited amounts of food and shelter. Consequently, no matter how good the sanitation, most buildings in which food is stored, handled or used will support house mice if not mouse-proofed. Although good sanitation will seldom eliminate mice, poor sanitation is sure to attract them and will permit them to thrive in greater numbers. Good sanitation will also reduce food and shelter for existing mice and in turn make baits and traps more effective. Pay particular attention to eliminating places where mice can find shelter. If they have few places to rest, hide or build nests and rear young, they cannot survive in large numbers.
Mouse-Proof Construction. The most successful and permanent form of house mouse control is to "build them out" by eliminating all openings through which they can enter a structure. All places where food is stored, processed or used should be made mouse-proof. Dried grain and meat products should be stored in glass jars, metal canisters or other resealable airtight containers.
Seal any openings larger than 1/4 inch to exclude mice. Steel wool mixed with caulking compound makes a good plug. Patching material needs to be smooth on the surface to prevent mice from pulling out or chewing through the patching compound. Seal cracks and openings in building foundations and openings for water pipes, vents and utilities with metal or concrete. Doors, windows and screens should fit tightly. It may be necessary to cover the edges with metal to prevent gnawing. Plastic sheeting or screen, wood, rubber or other gnawable materials are unsuitable for plugging holes used by mice
Traps. Trapping is an effective control method. When only a few mice are present in a building, it is usually the preferred control method. Trapping has several advantages: (1) it does not rely on inherently hazardous poisons, (2) it permits the user to make sure that the mouse has been killed and (3) it allows for disposal of the mouse carcasses, thereby avoiding dead mouse odors that may occur when poisoning is done within buildings.
The simple, inexpensive wood-based snap trap is effective and can be purchased in most hardware and grocery stores. Bait traps with peanut butter, chocolate candy, dried fruit or a small piece of bacon tied securely to the trigger. Set them so that the trigger is sensitive and will spring easily. Multiple-capture live traps, which can capture several mice once set, are also available in some hardware and feed stores. Set traps close to walls, behind objects, in dark corners and in places where evidence of mouse activity is seen. Place them so that mice will pass directly over the triggers as they follow the natural course of travel, usually close to a wall. Traps can be set on ledges or on top of pallets of stored materials if mice are active in such locations. Use enough traps to eliminate the rodents quickly. (Using too few traps is a common error by individuals attempting to control mice.) Mice seldom venture far from their shelter and food supply, so place traps no more than 10 feet apart in areas where mice are active. Leaving traps unset until the bait has been taken at least once (prebaiting) often increases the success of trapping. An alternative to traps are glue boards, which catch and hold mice attempting to cross them in much the same way flypaper catches flies. Place glue boards along walls where mice travel. Two or three glue boards placed side-by-side (or the larger glue boards used for rats) will be more effective than individual boards. Do not use them where children, pets or desirable wildlife can contact them. Glue boards can be placed inside tamper-resistant bait boxes in exposed locations. Glue boards lose their effectiveness in dusty areas unless covered and extremes of temperature also may affect the tackiness of the glue. Glue boards are sometimes used to catch a mouse that is wary of snap traps.
Poison Baits (Rodenticides). Rodenticides are poisons that kill rodents. They can be purchased in hardware stores, feed stores, discount stores, garden centers and other places where pesticides are sold. Do not buy unlabeled rodent baits from street vendors or other uncertain sources. Do not purchase baits that have an incomplete label or one that appears to be “homemade.”
“Building out” rodents and trapping are the most effective control methods. Rodent baits should be used only to supplement these methods. If there is a repeated need to use baits, it is likely that sanitation and mouse-proofing should be improved. Remember that rodent baits are poisons. Make sure they are registered with the U.S. Environmental Protection Agency and always follow the label instructions exactly. If baits are used indoors, be sure they are labeled specifically for interior use.
The active ingredients in baits are used at very low levels, so bait shyness does not occur when using properly formulated baits. Most of these baits cause death only after they are eaten for a number of days, although some types can cause death following a single feeding. Make sure that fresh bait is available continuously until mice stop feeding. Depending on the number of mice, this may require up to three weeks.
Bait Selection and Placement. Baits are available in several forms. Grain baits in a meal or pelleted form are available in small plastic, cellophane or paper packets. These sealed "place packs" keep bait fresh and make it easy to place the baits in burrows, walls or other locations. Mice gnaw into the packet to feed on the bait. Block style baits are also very effective for most situations. Proper placement of baits and the distance between placements is important. Place baits in several locations no farther than 10 feet apart and preferably closer. For effective control, baits or traps must be located where mice are living. Use of tamper-resistant bait stations provides a safeguard for people, pets and other animals. Place bait stations next to walls with the openings close to the wall or in other places where mice are active. When possible, secure the bait station to a fixed object to prevent it from being moved. Clearly label all bait stations "Caution—Mouse Bait" as a safety precaution.
Sound and Electronic Devices. Although mice are easily frightened by strange or unfamiliar noises, they quickly become accustomed to regularly repeated sounds and are often found living in grain mills or factories and other noisy locations. 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. Also, they lose their intensity quickly with distance. There is little evidence that sound of any type will drive established mice or rats from buildings because they rapidly become accustomed to the sound.
Control by Cats and Dogs. Although cats, dogs and other predators may kill mice, they do not give effective control in most circumstances. In fact, rodents may live in very close association with dogs and cats. Mice and rats may obtain much of their diet from the pet's dish or from what pets spill.
Disposal of Dead Rodents
Always wear intact rubber or plastic gloves when removing dead rodents and when cleaning or disinfecting items contaminated by rodents. Put the dead rodent in a plastic bag; the bag should be placed in a second bag and tightly sealed. Dispose of rodents in trash containers with tightfitting lids. Traps can be disinfected by soaking them in a solution of three tablespoons of bleach per gallon of water or a commercial disinfectant containing phenol (such as LysolR). After handling rodents, resetting traps and cleaning contaminated objects, thoroughly wash gloved hands in a general household disinfectant or in soap and warm water. Then remove gloves and thoroughly wash your hands with soap and warm water.
Prepared with the assistance of University of Illinois Extension. Always read and follow all current pesticide label instructions. If any information in these recommendations disagrees with the pesticide label, the label instructions must be followed. Use of a product name does not constitute product endorsement. For more information, contact the Illinois Department of Public Health, Division of Environmental Health, 525 W. Jefferson St., Springfield, IL 62761, 217-782-5830, TTY (hearing impaired use only) 800-547-0466.