Identification | Biology | Damage ID | Management | Handling
Overview of Damage Prevention
and Control Methods
- Practice proper sanitation – reduce sources of food, water, and shelter
- Store food in rodent-proof structures or containers, and properly store and dispose of refuse and garbage
- Control weeds and remove debris from around structures
- Rodent-proof construction – seal all openings larger than ¼ inch wide
- Cover openings with ¼-inch wire mesh or fill with stainless steel or copper wool
- Ultrasonic generally are not effective
Be sure to follow current EPA requirements; legal use of toxicants to control mice has been changing due to the number of accidental poisonings of non-targets (children and pets).
- Anticoagulant rodenticides
- Non-anticoagulant rodenticides
- Tracking powder
- Practical use of fumigants is limited to structures, containers, and commodities
- Shooting is not recommended
- Snap traps
- Cage and box traps (Sherman-type, Ketch-All®, Tin Cat®)
Other Control Methods
- Some cats and dogs catch individual mice, but they cannot be depended upon for control of populations of house mice
Damage Prevention and Control Methods
Integrated Pest Management
Timing, Economics, and Methods
Mice are active year-round and should be controlled as soon as they are noticed. Effective prevention and control of damage involves sanitation, rodent-proof construction, and reduction of the population with traps and toxicants. Sanitation and rodent-proofing are useful to prevent damage by mice, but when an& infestation already exists, population reduction likely is necessary.
The control of mice differs in important ways from controlling rats. Mice can enter narrower openings, thereby increasing the difficulties with rodent-proofing. Mice have limited home ranges and require little or no free water. Mice also have a higher reproductive capacity than rats and& usually are less sensitive to rodenticides. After rats are controlled at a given location, the number of mice may increase through immigration and reproduction, as habitats suitable for rats usually are suitable for mice.
Accurate data on damage by and cost of control of mice are difficult to obtain. In a survey of grain elevators in a Midwestern state, 76% of 1,000 corn samples were contaminated with droppings of rodents. Droppings of mice outnumbered droppings of rats 12:1. A mouse produces about 36,000 droppings per year.
Mice are very destructive to rigid foam, fiberglass batting, and other types of insulation in walls and attics of facilities. In a small swine finishing building near Lincoln, Nebraska, damage by rodents required the producer to spend $10,000 in repairs to the facility only 3 years after the initial construction.
Sanitation, which includes good housekeeping practices, along with proper storage and handling of food, animal feed, and garbage, is stressed for control of rodents. Even the best sanitation will not eliminate mice, although it will permit easier detection of sign, increase effectiveness of traps and bait by reducing competing food, and prevent large populations.
House mice are less dependent on humans than Norway rats, though both are adapted to living with people. Mice require little space and small amounts of food. They may inhabit buildings before construction is complete. In offices, mice may live behind cabinets or furniture and feed on scraps or crumbs from food& kept in desks. In homes, they find ample food in kitchens. In garages they eat sacked or spilled food for pets, grass seed, and insects. Most buildings in which food is stored, prepared, or consumed will support at least a few mice, regardless of sanitation. Sites must continuously be monitored for mice.
Store bulk and pet foods in rodent-proof containers, such as metal containers with tight-fitting lids. Stack sacked and boxed foods in rows on pallets in a way that allows thorough inspection for evidence of rodents. Store materials at least 8 inches away from walls. A 12-inch, white band painted on the floor adjacent to the wall will aid in detecting droppings of rodents and other signs. Sweep floors frequently to enable detection of fresh signs. Left-over food in pet dishes is a common source of food for rodents in and around homes. Give pets only what they will eat at a single feeding.
House mice can jump up to 10 inches from a flat surface. Keep pallets used to store food or feed at least 1 foot off the ground. Mice climb well and can walk up surfaces such as wood or concrete, unless the surface has a slick finish. Mice can live for long periods of time within a pallet of feed without going to the floor.
Keep the perimeter of buildings and other structures clean of weeds and debris, including stacked lumber and firewood, to discourage mice and to allow easier detection of sign. A 1½-foot wide strip of heavy gravel adjacent to foundations, known as a weed-free zone, may reduce burrowing.
“Rodent-proofing” is considered a critical aspect of controlling house mice. Build structures to exclude rodents. Inspect existing structures to identify ¼-inch openings through which mice could gain access. Examine outside and inside sill plates, foundations, door thresholds, utility lines, and other points of entry. Seal openings larger than ¼ inch wide with hardware cloth. Copper Stuff-Fit and Xcluder® fabric can be used to secure small crevices and gaps. Foam that expands is useful to reduce heat-loss but will not prevent rodent entry.
House mice are wary and easily frightened by unfamiliar sounds that come from new locations. Unusually loud and novel sounds frighten mice and cause temporary avoidance. However, mice quickly can become accustomed to new sounds if they repeatedly hear them.
Ultrasonic sound has very limited usefulness in the control of rodents. Ultrasound is directional, does not travel well around corners, and is easily attenuated. Ultrasound has limited range and rapidly loses intensity as it leaves the source.
Tests of commercial ultrasonic devices have indicated that rodents may be repelled from the immediate area of the ultrasound for a few days. Other tests have shown the degree of repellency depends on the particular frequencies used, intensity, and pre-existing condition of the infestation. Until more conclusive information is available, commercial ultrasonic devices are not recommended as a solution to infestations.
Rodents find some types of tastes and odors objectionable, but chemical repellents are seldom practical solutions for resolving infestations of mice. Ro-Pel® is registered for use in repelling mice from trees, poles, fences, shrubs, garbage, and other objects. Little information is available on its effectiveness against mice.
A variety of natural oils, including mint oil and balsam fir oil, are sold as repellents for mice. Little information is available regarding the effectiveness of these products against mice.
Be sure to follow current EPA requirements; legal use of toxicants to control mice has been changing due to the number of accidental poisonings of non-targets (children and pets). Most states require a commercial pesticide applicators license before applying rodenticides as a business service. General Use Pesticides (GUP) are toxicants that homeowners can purchase over-the-counter without a license for use on their own property. The Environmental Protection Agency (EPA) has taken steps to limit access to rodenticides based on active ingredient and type of application. Always read the label and check the most recent regulations. Rodenticides are classified as anti-coagulant and non-anticoagulant.
House mice are susceptible to all anticoagulant rodenticides (Tables 1 and 2), but generally are less sensitive to the active ingredients than rats. Nevertheless, anticoagulants provide good to excellent control of mice when they are prepared in baits. First-generation anticoagulants (warfarin, diphacinone, and chlorophacinone) usually require more feedings to produce death than second generation anticoagulants (brodifacoum, bromadiolone, difenacoum, and difethilone).
All anticoagulant baits are used similarly because they have similar modes of action. Anticoagulant rodenticides are slow-acting, so subsequent illness is not associated with the bait, even if a sub-lethal dose is consumed. Bait shyness usually does not occur and pre-baiting is not needed with anticoagulant rodenticides.
Table 1. First-generation anticoagulant rodenticides (multi-feed) that are General Use Pesticides (GUP) for controlling house mice.
|Common Name||Percent Active Ingredient|
0.2 (tracking powder)
0.2 (tracking powder)
Table 2. Second-generation anticoagulant rodenticides (single feed) that are Restricted Use Pesticides (RUP) for controlling house mice.
|Common Name||Percent Active Ingredient|
|Brodifacoum||0.0025 to 0.005|
Directions on the label commonly instruct the user to “maintain a continuous supply of bait for 15 days or until feeding ceases,” thus ensuring that all mice have ample opportunity to ingest lethal doses of the bait. Anticoagulants have the same effect on nearly all warm-blooded animals: they inhibit clotting of the blood and impair capillary action. Sensitivity to anticoagulants, however, varies among species. In general, the risk of non-target primary and secondary poisoning from anticoagulants is relatively low. Fortunately, vitamin K is an antidote for all anticoagulant intoxication.
Resistance to anticoagulants
Within any population of house mice, some individuals are less sensitive to anticoagulants than others. Where anticoagulants have been used for several years, the potential for a rodent population to be somewhat resistant to their lethal effects increases. Failure to achieve control with anticoagulant baits, even when baits are highly accepted, may be due to:
- too short of an exposure period to the bait,
- insufficient amount of bait,
- insufficient replenishment of bait (none remains from one baiting to the next),
- too few bait stations and too far apart; stations should be within 20 to 30 feet of each other in areas where mice are active,
- small area of control that permits mice to move in from adjacent areas, and
- genetic resistance to the anticoagulant, although unlikely, should be suspected if the same amount of bait is taken on a daily basis for several weeks with no appreciable reduction in rodents.
Failure to achieve control with anticoagulant baits that are poorly accepted may be due to:
- poor choice of bait, or bait that is improperly formulated,
- improperly placed bait stations,
- abundance of other food, and
- bait that is moldy, rancid, infested with insects, or contaminated with other material that reduces acceptance. Periodically remove old bait, dispose of it according to label instructions, and replace it with fresh bait.
Occasionally, mice accept bait well, resulting in an initial reduction of the population. However, acceptance of bait may drop, even though some mice remain. In such instances, the remaining mice probably never accepted the bait, either because of its formulation or placement. The best strategies are to switch to a different formulation, place baits at different locations, and use other methods of control such as traps. If resistance to first-generation anticoagulants is known or suspected, use of these compounds should be avoided in favor of the second-generation anticoagulants, or a non-anticoagulant product.
Three non-anticoagulant rodenticides are registered by the EPA for use against house mice (Table 3). All potentially are useful for controlling anticoagulant-resistant populations.
Bromethalin and cholecalciferol are formulated to serve as chronic rodenticides. They are applied so that mice have the opportunity to feed on the baits 1 or more times over 1 to several days. Acceptance of bait generally is good& with proper formulations. Bromethalin is formulated in ready-to-use bait. It is slow-acting, so bait-shyness usually is not a problem, and prebaiting is not necessary for good control in most situations. Cholecalciferol also is slow-acting, which eliminates bait-shyness, and death occurs after 3 or 4 days. Rodents typically cease feeding once a lethal dose has been ingested.
Zinc phosphide differs from the other 2 compounds in that prebaiting is recommended to increase acceptance of bait. Do not leave zinc phosphide baits for more than a few days, as continued exposure likely will result in bait-shyness within the population. Bait shyness occurs when bait produces an ill effect, but not death, within a few hours of consumption. Intoxicated animals often associate the bait with the illness, and thereafter avoid it. Avoidance can persist for weeks or months, and may be transferred to nontoxic foods of similar types. Prebaiting will reduce sub-lethal doses and thus bait-shyness. Always follow the directions on the label.
Table 3. Non-anticoagulant rodenticides and the percent of active ingredient commonly used for control of mice.
|Common Name||Percent Active Ingredient|
|Zinc Phosphide||2.0 |
10.0 (tracking powder)
Bait Selection and Formulation
Mice have poor eyesight and rely on hearing, smell, taste, and touch. They are considered color-blind, so bait can be dyed distinctive colors without causing avoidance, as long as the dye does not have an objectionable taste or odor. Food preferences may vary among populations and individual mice. It is important, particularly in moderate- to large-scale control programs, to check for differences in bait acceptance prior to investing time and money in a specific product. Use non-toxic versions of formulations of baits if available, to test acceptance by rodents. Place small amounts of bait about 4 inches apart in several locations where mice are present. Monitor consumption of baits to determine preferences. Ready-to-use baits come in a variety of formulations including powder, loose grain, pelleted, paste, blocks, and liquid. Mice often hoard food, which may result in bait being moved to places where it is undetected, difficult to recover, and hazardous to non-targets. Grain and pelleted baits can be carried easily by mice to other locations. Conversely, wax and extruded blocks can be secured within bait stations and are resistant to spoilage in moist areas, such as sewers. Mice accept paraffin block baits less readily than loose- or pelleted-grain baits. Baits similar to foods which mice are accustomed to often work well, particularly if food is limited or is made less available.
When water is unavailable, foods with high moisture content often are more readily accepted than dry baits. Rodents can detect the presence of anticoagulants in water baits more easily than in food baits. Up to 5% sugar often is added to liquid baits to increase acceptance. Water is attractive to most animals, so use treated water in bait boxes and other ways that prevent non-target animals from drinking.
Bait stations (bait boxes) may increase the effectiveness and safety of rodenticides. Bait stations are useful because they:
- protect bait from moisture and dust,
- provide a protected place for rodents to feed,
- keep non-target animals and children away from hazardous bait,
- allow placement of baits in locations where it would otherwise be difficult because of weather or potential hazards to non-targets,
- help prevent the accidental spilling of bait, and
- allow easy inspection of bait to see if rodents are feeding on it.
Types of Bait Stations
Bait stations can contain solid, liquid, or paste baits, and traps. Bait boxes can be purchased from commercial suppliers or made at home.
Bait boxes made of plastic, card-board, or metal are available in sizes for rats and mice. Some farm supply and agricultural chemical supply stores have them in stock or can order them. Choose tamper-resistant bait stations where children, pets, or livestock are present.
Secure bait stations to buildings by nailing or gluing them to walls or floors, so nothing can knock them over or shake the bait out.
Bait Station Maintenance
Provide enough fresh bait to allow rodents to eat all they want. When bait boxes initially are deployed, check them daily and add fresh bait as needed. After a short time, numbers of rodents and feeding will decline, and you only need to check the boxes every 2 to 4 weeks. If the bait becomes moldy, musty, soiled, or insect-infested, empty the box, clean it, and refill it with fresh bait. Dispose of spoiled or uneaten bait in accordance with the label. Follow all directions on the label of the product you are using.
If ants are feeding on the bait, apply insecticide or insect repellent on the ground below and around the bait station. Do not contaminate bait with insecticides. Mice usually will not be deterred by insecticides, provided the bait is not contaminated.
Use caution when cleaning stations heavily contaminated with droppings of rodents. Hantavirus is not associated with house mice, but it is with deer mice, which also may visit the station. Droppings and urine can contain other potentially dangerous pathogens. We recommend wearing a respirator (preferably full-face mask), gloves, and coveralls when cleaning contaminated bait stations. Consult CDC.gov for more information on protecting yourself from exposure to hantavirus.
Placement of Bait Stations
House mice usually are active in small areas. Proper placement of baits or bait stations is important. Mice will not visit bait stations, regardless of contents, if they are not located in areas where they are active.
Place bait between the shelter and food supply. Put bait boxes near burrows, against walls, and along travel routes. Where mice are living in sacked or boxed feed on pallets, bait or traps may have to be placed on top of stacks, or wedged in gaps within the stacks. Do not use baits that may contaminate food or toxic baits near consumables. Use traps and glue boards instead.
On farmsteads, placement of bait stations depends on design and use of the building. In confinement buildings for swine, it may be possible to attach bait boxes to ledges on walls or the top of walls that divide pens. Bait boxes may be placed in attics or along the floors and alleys where rodents are active. Tracks of rodents that are visible on dusty surfaces and droppings often give clues to where they are active.
Never place bait stations where children or non-target animals can knock them over. Spilled bait may become a hazard, particularly to small animals.
Permanent bait stations can be placed inside buildings that are not rodent-proof, along the outside of the foundation, and around the perimeter. Bait stations help keep populations low when regularly maintained with fresh anti-coagulant bait. Rodents moving in from nearby areas will be controlled before they can reproduce and cause significant damage.
Tracking powders have been used successfully for many years to control mice. When rodents walk through toxic powder, they pick it up on their feet and fur, and later ingest it while grooming. Tracking powders are useful for controlling mice where food is plentiful and good acceptance of bait is difficult to achieve. Bait-shyness rarely occurs with the use of tracking powders.
The amount of material a mouse may ingest while grooming is small, so the concentration of active ingredient in tracking powders is considerably higher than in food bait. Therefore, tracking powders can be more hazardous. Tracking powders are available only to licensed commercial applicators.
Place tracking powders only where they cannot contaminate food or animal feed, or where non-target animals cannot come into contact with them. Do not place tracking powders where mice can track the material onto food that is intended for humans or domestic animals. Tracking powders generally are not recommended for use in and around homes because of potential hazards to children and pets. Where possible, remove tracking powder after the control program is completed.
Fumigants are most commonly used to control mice in structures or containers such as feed bins, railcars, or other enclosed areas. Some fumigants are registered for use in burrows, however, burrows of mice cannot be fumigated efficiently or economically because they are small and often difficult to find. Control of mice by fumigation is practical and cost-effective only in very limited situations. Fumigants are hazardous and should be applied only by persons well-trained in their use and who possess the necessary safety equipment.
The shooting of mice is not recommended.
Control can be achieved with traps, but trapping requires more labor than other methods. It is recommended in situations where toxicants are inadvisable. The use of traps is the preferred method in homes, garages, and other structures where small numbers of mice may be present. The use of traps has several advantages:
- it does not rely on rodenticides,
- it permits the user to view his or her success, and
- it allows for disposal of the carcasses, thereby eliminating odor problems from decomposing carcasses that may remain with toxicants.
Use enough traps to make the control effort short and decisive. Mice seldom venture far from their shelter and food, so traps should be spaced no more than 6 feet apart in areas where mice are active. Although mice are not as afraid of new objects as rats, leaving the traps baited but unset, until the bait is taken at least once, will reduce the chance of mice escaping and becoming trap-shy.
Keep traps reasonably clean and in good working condition. Plastic and metal traps can be cleaned with a hotwater and a stiff brush. Always wear appropriate personal protective equipment (PPE). Female mice tend to avoid traps that have caught dominant males. It is recommended to monitor the sex of the mice that are caught. If captures are not evenly balanced between males and females, it is likely that you are missing a family unit. Check the web for details on how to identify the sex of mice. Wear gloves when handling mice.
Simple, inexpensive, wood-based, snap-traps are available in most hardware and farm-supply stores. Bait traps with peanut butter, marshmallows, hot dog, bacon, or nutmeat tied securely to the trigger. Commercially available non-allergenic baits also should be considered, especially in public use areas. Baits that are stale lose their effectiveness.
Set traps close to walls, behind objects, in dark places, and in locations where mouse activity is seen.
Place the traps so that when mice follow their natural course of travel, such as close to a wall, they pass directly over the trigger. Set traps so that the triggers are sensitive and spring easily. Effectiveness can be increased by enlarging the trigger or using traps with an expanded trigger. Attach a square of cardboard, metal, or wire-screen that fits just inside the wire bar of the trap. Clamshell-style traps are more expensive but allow for easier setting, cleaning, and removal of trapped mice.
Cage and Box Traps
Due to high costs, single-capture cage and box traps typically are not employed for the control of mice. If single-capture traps are chosen, solid wall, Sherman-style traps are recommended. Include a several cotton balls in the trap to provide a visual attractant. Smear peanut butter onto a square of wax-paper and fold the paper, to help prevent peanut butter from smearing all over the traps, or glue seeds onto wax-paper. Multiple-capture (automatic) mouse traps, such as the Ketch-All® and Victor Tin Cat® are available from hardware and farm-supply stores, or from distributors of pest-control equipment.
Glueboards catch and hold mice that attempt to cross them, in the same way flypaper catches flies. Glueboards have a lower rate of capture than other traps. Gluboards should not be used as the primary tool for controlling mice.
Place glueboards where mice travel, such as along walls. Glueboards lose their effectiveness in dusty areas unless they are covered, and extreme temperatures may affect the tackiness of some glue. Glueboards can be purchased ready-to-use, or they can be made. Do not place peanut butter directly on a glueboard, as the oil will dissolve the glue. Place peanut butter inside a plastic bottle cap and then situate the cap in the middle of the glue board. Do not use glueboards where non-target animals can contact them. Non-target catches can be released using vegetable oil to dissolve the glue. Some organizations oppose the use of glueboards.
Other Control Methods
In urban and suburban areas, it is common to find mice living in close association with cats and dogs, relying on pet food nourishment. Mice frequently live beneath dog houses and feed when dogs are absent or asleep. Some dogs and cats catch and kill mice, but pets generally do not control large populations. Around most structures, mice can find many places to hide and rear their young out of the reach of predators. Cats may not eliminate existing populations, but in some situations they may be able to prevent re-infestation. Cats place owners at increased risk exposure to toxoplasmosis, and the impact of free-ranging cats on native wildlife is a concern.