NY-03571 NJ-94544A CT-B1575
Pest Of The Month
Serving
Westchester, Putnam, Dutchess, Rockland, Orange, Bronx And Fairfield Counties
House Mouse
OTHER COMMON NAMES
English: Mouse Spanish: Ratón común.
PHYSICAL CHARACTERISTICSBody length 5.1-9 in (13-20 cm); tail 2.3-3.9 in (6-10 cm); weight 0.6-0.8 oz (18-23 g). A typical, stereotypical mouse, with grayish brown hair on its top, relatively big ears, and a dusky scaly, nearly hairless tail; the fur on its bottom is only slightly lighter than the fur on its top, and it has ungrooved incisors.
HABITAT
Underground burrows, which some subspecies equip with storage rooms. Each mouse will make its own nest, but will share burrows with other individuals in the colony. Many house mice are co-habitants with humans, living beneath large appliances or inside of walls in human homes. Some house mice live temporarily in grain fields, which they migrate into, breed, feed, and leave when the field is plowed; in 1926-1927, house mice nearly took over the fields of California's Central Valley, living in them in a density of 202,000 mice per 2.5 acres (1 ha). Sometimes, they eat animal and plant pests in the fields, but they inevitably wind up in barns and silos where they tend to contaminate food. In general, the house mouse does not stray far from cover, with the best habitat offering copious amounts of food, water, and places to hide. Their home ranges vary, from 120 ft (36.5 m) for some indoor mice to more than 2 mi (3.2 km) for certain ones outside.
BEHAVIOR
A social species, it lives in groups with others of its kind, and aggressive males have hierarchical ranks and tend to dominate colonies. Each group lives in a territory bound by scent markers, and animals within the colony have their own nests. They will groom each other and display aggressive and submissive postures common in the species.
FEEDING ECOLOGY AND DIET
Eat up to 10% of their body weight daily, and feed up to 20 times each day. They consume grains, fruits, vegetables, meat, insects, and have been known to eat glue, paste, and even soap. If they eat moist food or a seed diet of 12% protein, they can live without water. The house mouse has been known to feed on caterpillars, flightless moths, and earthworms.
REPRODUCTIVE BIOLOGY
Polygynous. They reproduce copiously, and a biological contraceptive keeps their populations in check: females' ovaries become inoperative and the animals become infertile. They breed throughout the year, with females giving birth to litters of 3-12 offspring about 5-10 times annually. Gestation is about three weeks. When the young arrive, they are hairless and their eyes are closed. Young are weaned by 21 days, they begin to reproduce in their second month of life, and they can live, depending on predation, to be six years old. Most wild mice live about a year, while those in captivity generally live about two years.
Rats are some of the most troublesome and damaging rodents in the United States. They consume and contaminate food, damage structures and property, and transmit parasites and diseases to other animals and humans. Rats live and thrive under a wide variety of climates and conditions; they are often found in and around homes and other buildings, farms, gardens, and open fields.
IDENTIFYING THE RAT
People do not often see rats, but signs of their presence are easy to detect (see sidebar). In California the most troublesome rats are two introduced species: the Roof rat and the Norway rat. It is important to know which species of rat is present in order to place traps or baits in the most effective locations.
Norway Rats.
Norway rats (Rattus norvegicus), sometimes called brown or sewer rats, are stocky burrowing rodents that are larger than roof rats. Their burrows are found along building foundations, beneath rubbish or woodpiles, and in moist areas in and around gardens and fields. Nests may be lined with shredded paper, cloth, or other fibrous material. When Norway rats invade buildings, they usually remain in the basement or ground floor. The Norway rat occurs throughout the 48 contiguous United States. Generally it is founds at lower elevations but may occur wherever people live.
Roof Rats.
Roof rats (Rattus rattus), sometimes called black rats, are slightly smaller than Norway rats. Unlike Norway rats, their tails are longer than their heads and bodies combined. Roof rats are very agile climbers and usually live and nest above ground in shrubs, trees, and dense vegetation such as ivy. In buildings, they are most often found in enclosed or elevated spaces in attics, walls, false ceilings, and cabinets. The roof rat has a more limited geographical area than the Norway rat, preferring ocean-influenced, warmer climates. In areas where the roof rat occurs, the Norway rat may also be present. If you are unsure of the species, look for rats at night with a strong flashlight or trap a few. There are several key physical differences between the two species of rats; Table 1 summarizes identifying characteristics.
Identifying Characteristics of Adult Rats.
Characteristic Roof rat Norway rat
general appearance sleek, agile, large, robust
color of belly gray to white mostly grayish
body weight 5 to 10 ounces 7 to 18 ounces
tail extends at least to snout; black, fine scales shorter than body; dark above; pale below; scales
head muzzle pointed muzzle blunt
ears long enough to reach eyes if folded over do not reach eyes
While rats are much larger than the common house mouse or meadow vole, a young rat is occasionally confused with a mouse. In general, very young rats have large feet and large heads in proportion to their bodies, whereas those of adult mice are much smaller in proportion to their body size. While both rats and mice gnaw on wood , rats leave much larger tooth marks than those of a mouse.
How to Spot a Rat Infestation
Because rats are active throughout the year, periodically check for signs of their presence. Once rats have invaded your garden or landscaping, unless your house is truly rodent proof, it is only a matter of time before you find evidence of them indoors. Experience has shown it is less time consuming to control rodents before their numbers get too high, and fewer traps and less bait will be required if control is started early. Inspect your yard and home thoroughly. If the answer to any of the following questions is yes, you may have a rat problem.
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Do you find rat droppings around dog or cat dishes or pet food storage containers?
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Do you hear noises coming from the attic just after dusk?
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Have you found remnants of rat nests when dismantling your firewood stack?
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Does your dog or cat bring home dead rat carcasses?
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Is there evidence rodents are feeding on fruit/nuts that are in or falling from the trees in your yard?
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Do you see burrows among plants or damaged vegetables when working in the garden?
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Do you see rats traveling along utility lines or on the tops of fences at dusk or soon after?
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Have you found rat nests behind boxes or in drawers in the garage?
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Are there smudge marks caused by the rats rubbing their fur against beams, rafters, pipes, and walls?
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Do you see burrows beneath your compost pile or beneath the garbage can?
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Are there rat or mouse droppings in your recycle bins?
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Have you ever had to remove a drowned rat from your swimming pool or hot tub?
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Do you see evidence of something digging under your garden tool shed or doghouse?
BIOLOGY AND LIFE CYCLE OF THE RAT
Rats, like house mice, are mostly active at night. They have poor eyesight, but they make up for this with their keen senses of hearing, smell, taste, and touch. Rats constantly explore and learn about their environment, memorizing the locations of pathways, obstacles, food and water, shelter, and other elements in their domain. They quickly detect and tend to avoid new objects placed into a familiar environment. Thus, objects such as traps and baits often are avoided for several days or more following their initial placement. While both species exhibit this avoidance of new objects, it is usually more pronounced in roof rats than in Norway rats.
Both Norway and roof rats may gain entry to structures by gnawing, climbing, jumping, or swimming through sewers and entering through the toilet or broken drains. While Norway rats are more powerful swimmers, roof rats are more agile and are better climbers.
Norway and roof rats do not get along. The Norway rat is larger and the more dominant species; it will kill a roof rat in a fight. When the two species occupy the same building, Norway rats will dominate the basement and ground floors, with roof rats occupying the attic or second and third floors. Contrary to some conceptions, the two species cannot interbreed. Both species may share some of the same food resources but do not feed side-by-side. Rats may grab food and carry it off to feed elsewhere.
Rats of either species, especially young rats, can squeeze beneath a door with only a 1/2-inch gap. If the door is made of wood, the rat may gnaw to enlarge the gap, but this may not be necessary.
Norway rats eat a wide variety of foods but mostly prefer cereal grains, meats, fish, nuts, and some fruits. When searching for food and water, Norway rats usually travel an area of about 100 to 150 feet in diameter; seldom do they travel any further than 300 feet from their burrows or nests. The average female Norway rat has four to six litters per year and may successfully wean 20 or more offspring annually.
Roof Rats.
Like Norway rats, roof rats eat a wide variety of foods, but their food preferences are primarily fruits, nuts, berries, slugs, and snails. Roof rats are especially fond of avocados and citrus and often eat fruit that is still on the tree. When feeding on a mature orange, they make a small hole through which they completely remove the contents of the fruit, leaving only the hollowed out rind hanging on the tree. The rind of a lemon is often eaten, leaving the flesh of the sour fruit still hanging. Their favorite habitats are attics, trees, and overgrown shrubbery or vines. Residential or industrial areas with mature landscaping provide good habitat, as does riparian vegetation of riverbanks and streams. Roof rats prefer to nest in locations off the ground and rarely dig burrows for living quarters if off-the-ground sites exist.
Roof rats routinely travel up to 300 feet for food. They may live in the landscaping of one residence and feed at another. They can often be seen at night running along overhead utility lines or fence tops. They have an excellent sense of balance and use their long tails for balance while traveling along overhead utility lines. They move faster than Norway rats and are very agile climbers, which enables them to quickly escape predators. They may live in trees or in attics and climb down to a food source. The average number of litters a female roof rat has per year depends on many factors, but generally is three to five with from five to eight young in each litter.
Rats consume and contaminate foodstuffs and animal feed. They also damage containers and packaging materials in which foods and feed are stored. Both species of rats cause problems by gnawing on electrical wires and wooden structures (doors, ledges, in corners, and in wall material) and tearing up insulation in walls and ceilings for nesting.
Norway rats may undermine building foundations and slabs with their burrowing activities. They may also gnaw on all types of materials, including soft metals such as copper and lead as well as plastic and wood. If roof rats are living in the attic of a residence, they can cause considerable damage with their gnawing and nest-building activities. They also damage garden crops and
ornamental plantings
Among the diseases rats may transmit to humans or livestock are murine typhus, leptospirosis, trichinosis, salmonellosis (food poisoning), and ratbite fever. Plague is a disease that can be carried by both roof and Norway rats, but in California it is more commonly associated with ground squirrels, chipmunks, and native wood rats.
MANAGING A RAT PROBLEM
Three elements are necessary for a successful rat management program: sanitation measures, building construction and rodent proofing, and, if necessary, population control.
Sanitation
Sanitation is fundamental to rat control and must be continuous. If sanitation measures are not properly maintained, the benefits of other measures will be lost, and rats will quickly return. Good housekeeping in and around buildings will reduce available shelter and food sources for Norway and, to some extent, roof rats. Neat, off-the-ground storage of pipes, lumber, firewood, crates, boxes, gardening equipment, and other household goods will help reduce the suitability of the area for rats and will also make their detection easier. Garbage, trash, and garden debris should be collected frequently, and all garbage receptacles should have tight-fitting covers. Where dogs are kept and fed outdoors, rats may become a problem if there is a ready supply of dog food. Feed your pet only the amount of food it will eat at a feeding, and store pet food in rodent-proof containers.
For roof rats in particular, thinning dense vegetation will make the habitat less desirable. Climbing hedges such as Algerian or English ivy, star jasmine, and honeysuckle on fences or buildings are very conducive to roof rat infestations and should be thinned or removed if possible, as should overhanging tree limbs within 3 feet of the roof. Separate the canopy of densely growing plants such as pyracantha and juniper from each other and from buildings by a distance of 2 feet or more to make it more difficult for rats to move between them.
Building Construction and Rodent Proofing
The most successful and long lasting form of rat control in buildings is to "build them out." Seal cracks and openings in building foundations, and any openings for water pipes, electric wires, sewer pipes, drain spouts, and vents. No hole larger than 1/4 inch should be left unsealed to exclude both rats and house mice. Make sure doors, windows, and screens fit tightly. Their edges can be covered with sheet metal if gnawing is a problem. Coarse steel wool, wire screen, and lightweight sheet metal are excellent materials for plugging gaps and holes. Plastic sheeting, wood, caulking, and other less sturdy materials are likely to be gnawed away.
Because rats (and house mice) are excellent climbers, openings above ground level must also be plugged. Rodent proofing against roof rats usually requires more time to find entry points than for Norway rats because of their greater climbing ability. Roof rats often enter buildings at the roof line area so be sure that all access points in the roof are sealed. If roof rats are travelling on overhead utility wires, contact a pest control professional or the utility company for information and assistance with measures that can be taken to prevent this.
Population Control
When food, water, and shelter are available, rat populations can reproduce and grow quickly. While the most permanent form of control is to limit food, water, shelter, and access to buildings, direct population control is often necessary.
