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The House Mouse
Recognizing a Rodent Infestation
Keep Rodents Outdoors
Commercial and Farm Buildings
Disposal of Rodents and Rodent Droppings
Rats and mice can be found in and around every town and farm in the country. It is estimated that there is one rat for every person living in the United States. Rodents have followed man to almost all parts of the world. They have no respect for social class; they are equal opportunity pests.
Rats and mice are so closely linked to man they are called domestic rodents. Man supplies their three basic needs: food, shelter, and water.
Rodents are a threat to health, and they interfere with our economic and physical well being.
Rodents can be found in our homes, supermarkets, restaurants, livestock pens, and farm fields. Warehouses, grain mills, elevators, silos and corncribs are especially vulnerable to rodent infestation. Rodents will eat anything man or his livestock eats. They are active at night. Rats are seldom seen during the day except when populations are exceedingly large. Rats and mice can crawl through very small crevices, which makes it hard to confine their movement. Even if you can't see them, you may hear them moving after dark. If your pet paws at a wall or cabinet it may be after a lurking rodent. Cats and dogs are not much of a deterrent to rodents, however.
Usually, the first clue of a serious rodent problem is their droppings on the kitchen counter, in kitchen drawers, cabinets, or the pantry. When one dwelling is infested, it's likely the immediate neighborhood is, too. That's why rodents are so difficult for one homeowner to control. Rodents are a community problem. Effective control necessitates that all homeowners in a community work together to eliminate sources of food, water, and shelter. Rodents are persistent in their efforts to invade the home, but you can deal with them effectively if you know their capabilities.
The house mouse (Mus musculus) is by far the most common mammal on earth. Native to central Asia, the mouse arrived in North America with the first European colonists. Mice can now be found all across North America, in every state including coastal Alaska, and in all but northernmost Canada.
The mouse is very adaptable. It's an excellent swimmer, runner, climber and jumper. It can jump as high as 12 inches. Mice have excellent senses of smell, taste and touch. While they have poor eyesight, mice have good peripheral vision that allows them to detect movement. Outdoors, mice nest in weeds, rubbish, cracks in rocks or walls, or they will construct a network of tunnels below ground, with chambers for nests and storage, and several exits.
Each fall, the onset of cold weather causes mice to search for food and shelter. Mice are curious, and will enter any hole or crack as small as ¼-inch. If they like what they find inside better than what they had outside, you will have a mouse problem. Mice will nest in any hidden area near a source of food. Their nests are constructed of rags or paper lined with finely shredded material, and look like a loosely woven ball 4-6 inches in diameter. If food is available, a mouse will normally travel no more than 10-50 feet from their nest. Mice are territorial, and will constantly explore to learn more about their surroundings. They memorize pathways, obstacles, food, water, shelter and other elements in their habitat. They are quick to detect new objects in their environment, and they are more curious than fearful of anything new.
Because of their poor eyesight, mice navigate using their whiskers, usually traveling along a wall or other object. If you don't move, a mouse can't see you. They will explore when they think they're alone...usually at night, but any other time when they don't detect movement. People usually see mice only when they have been sitting stock still, such as when reading or watching television. Unlike rats, the fact that you have seen a mouse does not necessarily mean they have a high population density.
A mouse family will include a dominant male, several females, and their young. Females will establish a loose hierarchy within their territory. Adult mice will force their young to disperse, although some females may remain close to their parents. The mouse is one of the most prolific of mammals.
It's easy to see why mouse populations can grow exponentially under the right conditions. Fortunately, breeding slows markedly as mouse populations increase.
While they will drink water when it's available, mice can live in a dry habitat, getting all the water they need from the food they eat. In the wild, mice eat seeds, roots, leaves and stems, beetle larvae, caterpillars, cockroaches, and carrion, but they prefer seeds and grain. Although mice can live on crumbs, typically they eat 3 grams of food per day (10-15% of their body weight), or about 8 pounds per year. When human food is available, those foods high in fat, protein, or sugar are often eaten in preference to seeds and grain. Some of their favorite human foods include bacon, chocolate, butter and nuts. Mice are naturally curious, and do not hesitate to sample new foods. They will even eat glue or soap, if the soap contains animal fat.
Mice nibble whatever food is available, eating small portions to find what they like best. In this manner, mice destroy much more food than they eat. In a year, one mouse will produce approximately 18,000 fecal droppings. They will store food, which can lead to insect infestations. Though it is not their preference, mice will live in freezers feeding only on frozen food. This usually occurs in large commercial operations that have walk-in coolers.
The Norway rat (Rattus norvegicus) is strong, very aggressive, and able to adapt to cold climates.
A rat will shed over 500,000 body hairs each year. Left untouched, a rat's incisor teeth would grow 4 inches in a year. So rats must chew continuously to wear down their incisors. Rats will chew on wood, aluminum siding, wallboard, plaster, paneling, frozen ground, concrete...anything but glass and most metals.
Because they are so adept at hiding and scurrying, rats can exist in large numbers unbeknownst to their human neighbors. Unlike the mouse, rats are fearful of anything new. Even so, they quickly adapt to new places to live, new routines, new places to eat, and new kinds of food.
People see rats more often from April through June (spring breeding), and again in October and November as the season changes. But rats are active year-round. Outdoors, rats burrow in earth banks, along walls, under rubbish or concrete slabs, but they always locate close to sources of food and water. Rats follow the same routes as they make their rounds foraging for food each night, so they leave obvious runways in the grass. Rats often travel under objects like bales, planks, granaries and machinery to conceal their movement. A rat will normally travel no more than 150 feet from its nest, but at harvest time rats will travel much further to forage for corn, wheat or beans left in farm fields.
Outdoors or indoors, rats leave obvious oil stains on their trails and entrance holes. They can enter any opening larger than ½-inch in diameter, which means they can squeeze into your home through
Rats will make holes in walls or floors soon after invasion. Rat holes are circular, average 2-3 inches in diameter, and are usually just inches off the floor. Holes in floors are generally close to walls. Rats leave behind a distinctive musk odor, particularly if they are confined to a small space.
Like the mouse, rats establish territories and colonies. The dominant male continuously guards his harem of females and aggressively prevents other males from mating. Females actively defend their group against strangers and often nest together. Their nests are constructed from leaves, paper, rags, twigs, or anything else they can find. Rats are nocturnal, but in areas having large rat populations some low ranked rats will forage during the day, because other rats have denied them access to food at night.
Rats are also profoundly prolific. If food and shelter are adequate, rats will breed throughout the year, although fewer litters are produced in winter.
It's easy to see why rat populations can grow exponentially. Under ideal conditions, a pair of rats could produce 15,000 offspring in one year. Fortunately, breeding slows markedly as populations increase.
Rats have voracious appetites. A rat can eat a third of its body weight each day. The rat is a true omnivore. It will eat anything, including soap, leather, furs, candy, milk, meat, vegetables, poultry, eggs, grain, seeds, fruit, nuts, snails and other rodents. Rats will catch fish, and they readily eat carrion. Near homes, rats thrive on pet food, birdseed, grass seed, garbage, dog feces, and the uneaten or spoiled food we discard. While rats will eat nearly anything, they prefer grain, livestock feed, and meat. Unlike the mouse, which nibbles a little at a time, rats will fill up at one sitting, if possible. Rats will hoard and cache food, which can result in insect infestations. Like mice, rats will live in freezers, feeding only on frozen food. Rats eat so much that one rat can leave behind 25,000 droppings per year. The rat's main constraint is that it cannot go long without water unless its diet supplies enough. Rats need up to one ounce of water every day.
The number and behavior of rats change throughout the year. Many rats die during winter, as outdoor foods become hard to find. Breeding in winter is comparatively low, so rat populations are at their lowest. A mild winter means fewer rats will die of natural causes, so more can be expected in the spring. But if rats are controlled in winter, fewer will be available to resume the breeding cycle in spring. Heavy breeding begins in March when the weather turns. Spring rains spur vegetation which provides cover and additional food. So rats are more abundant in late spring. Young rats have to seek food and new nests. In summer, food and vegetation are abundant, so rats continue breeding. Breeding peaks in early September as temperatures begin to fall. Sources of food and shelter start to diminish in fall, so rats look for shelter inside buildings and homes.
Getting rid of rats is difficult. Capturing or poisoning a few rats in the neighborhood makes little impact. To defeat them, a community has to cooperate in capturing or killing them, at the same time starving them, denying them shelter, and cutting off their sources of water. Denied a source of food, rats will turn to killing and eating each other, which further reduces the infestation.
There are twelve indicators of rodent activity:
The best way to control rodents is to keep them out of the home in the first place. Since rodents like to hide in vegetation, your first line of defense is to trim the vegetation close to your home. Clean yards deny rodents the food and shelter they need for breeding, and they restrict a young rodent's ability to move in. Piles of grass clippings or tree trimmings make ideal rodent harborages, so properly store and dispose of these materials. Try to leave a couple of feet of clear space between your house and any vegetation. Rodents also like to hide under woodpiles or lumber; in abandoned cars, appliances and furniture; and under trashcans. So remove and properly dispose of all junk. Store any lumber or wood on racks at least 6-inches off the ground, and away from the house exterior. Store your trash and garbage cans on racks too, or else on a concrete pad.
Check your house perimeter annually in late summer or early fall to assure there are no gaps that could be used for entry. Remember that a pencil-sized opening is sufficient for mouse entry. Pay special attention to pipes, wiring, conduits, cables, doors, and windows. Even where buried utility piping enters, the foundation must be effectively sealed. At night, have someone shine a light along the interior of your basement or crawl space walls while you circle the perimeter of the house on the outside. Potential entrance holes or other flaws you may not be aware of will show up under the light. Close any openings found, using sheet metal, hardware cloth, or wire mesh. Pieces of tin cut from coffee cans make great patches. Caulking will not do the job. Screen necessary openings, like fans and chimneys with ¼-inch wire mesh. Wire mesh greater than ¼-inch won't work. Replace missing bricks. Fill in any burrows under the foundation with concrete.
Attached garages are serious weak points, because garage doors rarely fit as closely as other doors. Once a rodent has made it into an attached garage, the rest of the house is easy pickings. Therefore, to make the garage less attractive, store your trash and garbage somewhere else. But if you must store it there, be especially careful to use containers in good condition with tight-fitting lids. Never leave plastic trash bags in an attached garage. Again, shine a light along the perimeter of your garage door at night to see if it offers easy entry. Check the doors of attached garages more often than once a year.
Windows and exterior doors should fit properly, be weather-stripped, and be kept closed when not in use. There should be no holes in screen doors. Screens are easy to patch. All window and door edges subject to gnawing should be covered with metal.
Even water puddles will give rodents all the water they need to drink. So all leaks must be fixed, and all ruts and depressional areas must be drained or filled in. Keep all guttering clean so water doesn't stand. Make sure your window air conditioner isn't creating a puddle. Cover swimming pools and hot tubs. Drain birdbaths and ornamental ponds. Water hoses are notorious for leaking at the connections; so when you're finished using the hose shut the water off at the spigot, rather than at the hose nozzle. Cease lawn sprinkling for the duration of the infestation.
Outside food sources that attract rodents include garbage, dog and cat food, dog feces, birdseed, and fruits or berries that have fallen to the ground. Take away their sources of food outside, and rodents will look for another neighborhood to live. Pick up fruit and vegetables in your yard. A honeycomb can feed hundreds of mice all winter, so carefully remove any beehives in the immediate area. Birds are messy eaters, which is especially helpful to rodents. So quit feeding the birds for the duration of the infestation. If you're feeding the squirrels; you're also feeding rodents. If at all possible, feed your pets indoors. If you must feed your pets outside, remove their food 30 minutes after serving. Otherwise, whatever your pet doesn't eat, rodents will. Since rats are nocturnal, feed your outdoor pet well before dark.
Store your garbage in containers preferably made of metal, with tight fitting lids. Never leave plastic trash bags outside. Turn compost piles regularly and don't compost meat, bones, dairy waste, fats, or oils. Remove dog feces from the yard daily.
Store bulk foods in rodent-proof buildings, rooms, or containers whenever possible. Stack packaged food on pallets with adequate space left around and under stored articles to allow inspection for signs of rats. Drain holes in dumpsters should be fitted with a removable hardware-cloth screen, or else plugged after each cleaning.
Although cats, dogs, and other predators sometimes kill rats, they do not provide effective rodent control. They just can't kill rats fast enough. Rats often live among cats and dogs. They use a pet's food and water, and sometimes even their shelter.
Use traps only after you've taken all the sanitation steps outlined above. While rodent trapping is a very important tool in rodent control, it is no substitute for good sanitation. If you don't control their sources of food and water, rodents will procreate faster than you can trap them. Trapping has the advantage that
Traps are particularly effective if rodent populations are small. Snap traps, glue boards, and cage traps all work. Most traps can be used over and over. Wood-based snap traps are inexpensive, and available at most hardware stores. Most snap traps are designed for mice but larger traps designed specifically for rats are available. Purchase enough traps to make your effort short and decisive.
Traps need not be baited, just located where rodents will trip across the trigger in their normal course of travel. If you want to bait your traps use a very tiny amount of peanut butter, gumdrops, raw bacon, bologna, or vanilla extract (use a cotton swab to apply vanilla extract). Whatever you use, don't pile it on. Do so, and you increase the chance for an insect infestation. You also increase the chance that a rodent will find a way to remove the bait without getting caught. You may also kill one rodent but feed several others. All you really want is the food smell. You can also bait with a piece of cotton ball, since rodents like to use it to build nests. Cotton has the advantage of not attracting insects.
Another form of trap is the glue board, which has a sticky surface that holds any rodent that attempts to cross it. Locate glue boards anywhere you would other traps, but remember that glue boards are so sticky that they'll be a problem for any children, livestock, pets or other wildlife that come in contact. Also keep in mind that dust will reduce the effectiveness of a glue board. Once caught on a glue board, a mouse will usually die from cardiac arrest. Glue boards will lose their effectiveness over time, so replace them when they are no longer sticky. As with any other trap, move your glue boards to another location if rodents are not being caught.
Ultrasonic devices broadcast sound waves above the range of human hearing, but they have limited efficacy because the sound waves produced cannot penetrate solid objects, like walls. They also quickly lose intensity with distance. Because rodents quickly become accustomed to repetitive sounds, there is little evidence that sound devices will drive established rats or mice from buildings. Likewise, there is little evidence that magnetic devices or vibrators have any positive effect on rodents.
Rodenticides are poisoned baits and fumigants used mainly by professionals for rodent control. Since fumigants are gases highly toxic to humans, livestock and other animals, they cannot be applied in buildings where occupants could be exposed. Rodenticides have a wide variety of active ingredients. They are registered pesticides available on the open market, but they require training and experience to apply safely and effectively. If not properly applied, these pesticides can kill or otherwise endanger children, pets, or other animals that may mistakenly eat or breathe them. We urge you not to use these materials yourself. Hire a licensed pesticide applicator well versed in rodent control to apply them. Sometimes rodenticides work too well. It can kill a rodent before it makes it out of the house. In that case you'll have dead rodents in inconvenient places like attics, wall cavities, crawl spaces, or behind cabinetry...stinking up your home and causing major insect and fly problems. Since rodenticides are pesticides, they also present serious storage and disposal problems.
Try not to touch a dead or dying rodent, or their droppings. Fleas on the rodent will want to make you their new host. Use rubber gloves or tongs and dispose of rodents and rodent droppings by burial, incineration, or by wrapping them in a plastic bag before throwing them into a tightly covered garbage can. Injured or sick rodents should be killed (drowning is easiest) before being disposed of. Dry sweeping or vacuuming will cause dust and viruses to become airborne. Therefore,
Wash your hands with soap and hot water after disposing of rodents and rodent droppings, even if you used gloves.
Results cannot be measured simply by counting dead rats and mice. Abandoned burrows will be dusty and have cobwebs in the openings. When there are no fresh tracks or droppings, and live rats or mice are no longer observable, results are as good as can be expected.
Additional information on preventing rodent infestations, diseases from rodents, cleaning up after rodents, and images of rats and mice can be obtained from the Centers for Disease Control and Prevention (CDC) web site.