The house mouse (Mus musculus) easily adapts to life with people. It thrives in a wide range of climatic conditions in a great variety of habitats, feeding on most human food, and reproducing at a remarkable rate. House mice are found in most areas of human habitation. House mice are also found living in the wild. Pest control operators often find that the house mouse is the most troublesome and economically important rodent. House mice are a common problem in homes and in all types of businesses. Nearly everyone can remember times when they were irritated by mice. They are a nuisance to rich and poor alike. The continual drain that house mice impose on stored food and fiber, and the damage they cause to personal possessions, are the most serious economic threats. House mice also have the potential to transmit diseases and parasites to people and domestic animals.
Control of house mice requires understanding mouse biology and habits, and particularly the major differences between mice and rats. During the past few decades, control of Norway and roof rats has improved while problems with house mice have increased. Baiting programs often are more successful in controlling rats than they are in controlling mice. Many failures in mouse control can be blamed on an applicator using rat-control techniques. The house mouse easily adapts to life with people. Pest control applicators will find that the house mouse is the most troublesome and economically important rodent. Mice are a nuisance, can cause damage to food and buildings and have the potential to transmit disease and parasites. The house mouse is a small, agile rodent. House mice vary in colour from light brown to dark grey but most often are a medium brown or dusky grey, except the belly, which may be a lighter shade than their general colour, but never white. The mouse has moderately large ears. The tail is nearly hairless and about as long as the body and head combined. The feet and eyes are small.
Losses Due to Mice
When mice infest stored food, the greatest loss is not what mice eat, but what is thrown out because of real or suspected contamination. In six months, one pair of mice can eat about four pounds of food and deposit about 18,000 droppings. The amount of food contaminated by the mice is estimated to be about ten times greater than what is eaten. So common are mice that the government permits a certain number rodent hairs, and sometimes droppings, to remain in food commodities destined for human consumption.
Yet food inspectors often have to condemn food products and fine manufacturers because of house mouse contamination in excess of that permitted. Losses are not only connected with food. Family bibles or heirlooms stored in a trunk in the attic or garage that are damaged by mice are irreplaceable, as are original paintings and manuscripts stored in museums. Mouse-riddled documents in the bottom file drawer of an office cannot generally be valued in dollars and cents, but these losses can be costly. Electrical wiring gnawed by rodents start many fires. Many listed as cause unknown” are probably rodent-related. House mice frequently take up residence in electrical appliances and end up chewing into the power supply. This is particularly costly when computer systems are disrupted.
Habits of House Mice
Under ideal conditions, the house mouse may produce as many as 10 litters (about 50 young) in a year. Environmental conditions, such as the availability and quantity of food, play a role in the frequency of pregnancies, litter size and survival. New-born mice are quite undeveloped and are nearly hair-less. At about 3 weeks, the young start to eat solid food and take trips on their own.
1 Social Behaviour
Mice are primarily active at night. Movements of house mice are primarily determined by temperature, food and hiding places. Home ranges of mice tend to be the smallest when living conditions are good. Mice tend to travel over their territory daily, investigating any changes or new objects. They are very aggressive and show no fear of new objects.
2 Senses of Mice
Mice have relatively poor vision and are color blind. They rely heavily on smell, taste, touch and hearing. An important sensory factor with mice is touch. Like rats, they use their long whiskers and guard hairs to enable them to travel. Mice also have an excellent sense of balance.
Mice quickly detect new objects in their territory and investigate. They will immediately enter bait stations and sample a new food (although they normally only nibble the food). They will also investigate traps and glue boards. Because of this curiosity, control programs against mice are often successful early, with the opposite being true for rats.
4 Physical Attributes
The pest control applicator must understand what a house mouse is capable of in order to effectively plan a control program.
- Mice are excellent jumpers.
- They can jump against a wall or flat vertical surface and use it as a spring board for added height.
- They can run up almost any vertical surface without much difficulty if the surface is rough.
- They can run along extremely thin areas such as electrical wires.
- They can travel for some distance hanging upside down.
- They are capable swimmers although they do not take to water as well as rats do and they tend not to dive below the surface.
- They can walk or run along ledges too narrow for rats.
5 Food and Water
House mice prefer cereals over other items although they will feed on a wide variety of food. Mice get much of their water from their food but they will drink if water is available. Mice are nibblers and have two main feeding periods, at dusk and just before dawn.
Mice are territorial and seldom travel more than 10 m (30 feet) from their nest. Their range is much smaller than the rats’ range of 30 to 46 m (100 to 150 feet).
House mice may nest in any dark, sheltered location. Nests are constructed of any fibrous, shredded material such as paper, cloth, or insulation and generally look like a loosely woven ball. The small range of mice, the way they feed and their food preferences are the characteristics that set house mice apart from rats. Keep these in mind when controlling mice as many failures in mice control are due to an applicator using rat-control techniques.
Sounds are common at night where large numbers of mice are present.
- Listen for squeaks, scrambling and sounds of gnawing.
A house mouse produces about 70 droppings per day. Fresh droppings are not usually as soft in texture as rat droppings and in a few days become quite hard. Mouse droppings are frequently the first evidence that mice are infesting. Large cockroaches, bats, and other species of mice such as deermice (Peromyscus sp) and meadow mice (Mircrotus sp), may produce droppings similar to house mice.
- Look along runways, by food near shelters, and in other places mice may frequent.
House mice occasionally make small mounds known as “urinating pillars.” These consist of a combination of grease, urine, and dirt and may become quite conspicuous.
- Look for many small drops of urine.
- Use a blacklight. Urine stains will fluoresce under ultra-violet light.
4 Grease Marks
Like rats, mice produce greasy smears where dirt and oil from 0their fur marks pipes and beams. House mouse spotsare not as easy to detect.
- Expect markings to cover a smaller area than those made by rats.
Most house mouse runways are indistinct trails free of dust but not readily detectable.
- Look for footprints or tail marks on dusty surfaces or on mud.
- Use a nontoxic tracking dust to help to determine the presence of house mice within Buildings
7 Gnawing Damage
Recent gnawing on wood are light in colour, turning darkerwith age.
- Look for enlarged cracks beneath doors.
- Look for small tooth marks. (Such evidence frequently helps to distinguish between mice and rats).
- Look for wood chips with a consistency like coarse saw-dust around baseboards, doors, basement windows and frames, and kitchen cabinets.
8 Visual Sightings
Mice are often active in daylight and this may not indicate a high population as it does with rats.
- Use a powerful flashlight or spotlight at night in ware-houses and food plants to confirm house mouse presence.
9 Nest sites
- Look in garages, attics, basements, closets, and other storage places.
- Be alert to fine shredded paper or other fibrous materials; these are common nest-building materials.
10 Pet Excitement
- Follow up when cats and dogs paw excitedly at a kitchen cabinet door, the floor at the Base of a refrigerator, or atthe base of a wall, especially if mice have invaded the premises only recently.
11 Mouse Odors
- Smell for the characteristic musky odour produced by mice. It can be easily differentiated from that of rats.
Estimating Numbers of Mice
Estimates are more difficult to get than for rats. The numbers of mice observed or food consumed is not highly reliable as a census technique with house mice. Unlike rats (which maytravel widely within a building leaving tracks on many patches of dust) house mice do not range widely.
- Read natural signs such as droppings, urine stains, tracks, and damage.
- Make nontoxic tracking patches of talc at 5 to 10 meter intervals (20 to 30 feet) throughout a building. The more tracks seen in each patch, and the more patches showing tracks, the larger the population. The percentage of patches showing tracks, will reflect the extent of the local infestation.
- Tracking patches are also an excellent means to evaluate a control operation. Compare the number of tracks or patches with mouse tracks before and after a control program.
Control and Management
Control and prevention of house mice is a three-part process:
- mouse-proofing, and
- population reduction with traps or toxicants.
The first two are useful preventive measures. When a mouse population already exists, some kind of lethal control is necessary. Otherwise, the reproductive capability of the mice, and their remarkable ability to find food in almost any habitat, will keep their populations up or increase them. House mouse control is different from rat control. Applicators that do not take these differences into account will have control failures Sealing mice out of a building is difficult because mice are smaller. Range is small. Identify each infested site in order to target control procedures. Mice often can produce offspring faster than control methods can work. Nevertheless, many of the techniques to control and manage rats also apply to mice. In the sections below the differences in procedures between rats and mice are emphasized.
Good sanitation makes it easier to detect signs of mouse infestation. It also increases the effectiveness of baits and traps by reducing competing food. However, the best sanitation will not eliminate house mice; they require very little space and small amounts of food to flourish.
- Store bulk foods in mouse-proof containers or rooms. In warehouses, restaurants, and food plants stack packaged foods in orderly rows on pallets so that they can be inspected easily. A family of mice can happily live in a pallet of food without ever having to leave the immediate area.
- Keep stored materials away from walls and off of the floor. A 12 -18 inch yellow or white painted band next to the wall in commercial storage areas permits easier detection of mouse droppings. This band and the areas around pallets should be swept often so that new droppings can be detected quickly.
It isn’t easy to completely mouse-proof a building since mice are reported to be able to squeeze through an opening as little as 1/4-inch high.
- Seal large holes to limit the movement of mice into and through a building.
- Plug holes in foundation walls with steel wool or copper mesh.
- Caulk and fit doors and windows tightly. Seal holes around pipes, utility lines, vents, etc., to make it difficult for mice to move in and out of wall and ceiling voids. This confines mice to a smaller area and may make snap traps and glue boards more effective.
Snap Traps. If used correctly, snap traps are very effective in controlling mice. They must be set in the right places, in high numbers, and in the right position or mice will miss them entirely.
Here are some factors to keep in mind when trapping mice.
- Remember that the territory of mice rarely extends further than 30 feet from the nest, and more often is about 10 feet. If mice are sighted throughout a building it means that there are numerous discrete locations where you will have to set traps. Place snap traps not only wherever you see obvious signs of mice, but look for good trap locations in a three dimensionalsphere about ten feet in diameter around those signs.
- Mice can be living above their main food supply in suspended ceilings, attics, inside vertical pipe runs, and on top of walk-in coolers. Or they can be below, in floor voids, crawl spaces, or under coolers and/or processing equipment.
- The best sites are those with large numbers of droppings since that means the mice are spending a lot of time there. Other good sites are along walls, behind objects, and in dark corners, particularly where runways narrow down, funneling the mice into a limited area.
- Good mouse baits increase a traps effectiveness. Peanut butter, bacon, cereal, and nuts are traditional, but one of the best baits is a cotton ball, which the female mice like to use for nest material. It must be tied securely to the trigger. Food baits must be fresh to be effective.
- Probably the biggest mistake made in mouse trapping is not using enough traps. Use enough to make the trapping campaign short and sweet.
4 Multiple-Catch Traps
Multiple-catch mouse traps catch up to 15 mice without requiring reset. Some brands are called “wind-up” traps; the wind-up mechanism kicks mice into the trap. Others use a treadle door. Live mice must be humanely killed.
Mice like to investigate new things. They enter the small entrance hole without hesitation. Odor plays a role too; traps that smell “mousy” catch more mice. Place a small dab of peanut butter inside the tunnel entrance to improve the catch.
- Check traps frequently. Mice are captured alive but may die in a day or two. Some traps have a clear plastic end plate or lid so you can see if any have been captured.
- Place the traps directly against a wall or object with the opening parallel to the runway, or point the tunnel hole towards the wall, leaving one or two inches of space between the trap and the wall.
- If mice are active, place many traps 6-10 feet apart. For maintenance trapping, place the traps in high risk areas and also at potential mouse entry points such as loading docks, near utility lines, and at doorways.
5 Glue Boards
Glue boards are very effective against mice. As with traps, placement is the key. Locations thatare good trap sites are good sites for glue boards.
- Do not put glue boards directly above food products or in food preparation areas.
- Set glue boards lengthwise and flush against a wall, box, or other object that edges a runway.
- Move objects around; create new, narrow runways six inches wide to increase the effectiveness of glue boards.
- Put peanut butter or a cotton ball in the center of the board.
- Place the glue boards 5 to 10 feet apart in infested areas [closer if the population is large].
- If no mice are captured in three days, move the boards to new locations.
- If a trapped mouse is alive, kill it before disposal. Replace the boards if they fill up with insects.
Food Baits. Observe the same safety guidelines for mouse baits as discussed in the section on rat baits. Children, pets, wildlife, and domestic animals must be protected by putting the bait in inaccessible locations or inside tamper-proof bait boxes.
- Apply many small bait placements rather than a few large placements.
- Use baits labeled for mouse control.
- Place the baits in favorite feeding and resting sites as determined by large numbers of droppings.
- Place the baits between hiding places and food, up against a wall or object to intercept the mice.
- Bait in three dimensions (see earlier discussion on trapping).
- Make bait placements 10 feet apart or closer in infested areas.
- If bait is refused, try switching to a different type, and replace the baits often.
- Use small bait stations which are more attractive to mice than the larger rat-type stations.
- Make sure that sanitation is such that other food is not out- competing the baits.
- Place secured tamper-proof bait boxes in safe locations near doors in late summer to intercept mice entering from the wild.
7 Liquid Baits.
Mice get most of their water from their food; they also drink from a water container. Liquid baits that are labeled for mouse control can be effective in sites that do not have a ready supply of water. The same water bait dispensers used for rats can be used for mice. As with food baits and traps, many water stations will be necessary to put the bait into the territory of all mice infesting a building.
8 Tracking Powders.
Tracking powders are especially effective against mice. Mice groom themselves more than rats, and they investigate enclosed areas which can be dusted with tracking powder.
- Apply inside infested dry wall voids.
- Dust tracking powder into voids in heavily infested apartment or office buildings.
- Use a bait station, PVC tube, cardboard tube, or any small, dark shelter that a mouse could enter in cases where tracking powder cannot be applied. Mice will explore such a shelter.
- Apply the tracking powder in a layer less than 1/16-inch deep.
- Do not allow tracking powder to drift into nontarget areas.