Pest Information
House Mouse
Mus musculus
The house mouse (Mus musculus) is considered one of the most troublesome
and economically important rodents in the United States. House mice live
and thrive under a variety of conditions. They are found in and around homes
and farms as well as in open fields and agricultural lands. House mice consume
and contaminate food meant for humans, livestock, or other animals. They
cause damage to structures and property, and they may transmit diseases
such as salmonellosis (food poisoning).
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 non-descript, brownish rodents with relatively large ears
and small eyes. They weigh about 1/2 ounce and are usually light brownish
to light grayish. An adult 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 are sporadic feeders, 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. Mice can squeeze through openings slightly larger than 1/4
inch in diameter.
In a single year, a female may have five to ten litters of usually five
or six young each. Young are born 19 to 21 days after mating, and they reach
reproductive maturity in six to ten weeks. The life span of a mouse is about
nine to twelve months.
Mouse Control
Effective control involves three aspects: 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: Because mice can survive in very
small areas with limited amounts of food and shelter, it is almost impossible
to eliminate them, particularly on farms. Most buildings in which food is
stored, handled, or used will support house mice if not mouse-proofed, no
matter how good the sanitation. Although good sanitation will seldom eliminate
mice, poor sanitation is sure to attract them and will permit them to thrive
in greater abundance. Good sanitation will also reduce food and shelter
for existing mice and in turn make the 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, re-sealable
coffee cans, or other air tight 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 tightly 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.
It is the preferred method in homes, garages, and other structures where
only a few mice are present. Trapping has several advantages: 1) it does
not rely on inherently hazardous poisons; 2) it permits the user to confirm
that the mouse has been killed and 3) it allows for disposal of the mouse
carcasses, thereby eliminating dead mouse odors which 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. Leaving
traps baited but unset until the bait has been taken at least once reduces
the chance of creating trap-shy mice.
Multiple-capture live traps for mice such as the Victor Tin CatŪ and the
Ketch-AllŪ, 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 make the campaign
short and decisive. Mice seldom venture far from their shelter and food
supply, so space traps no more than about 10 feet apart in areas where mice
are active.
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. Do not use them where children, pets, or
desirable wildlife can contact them. Glue boards can be placed inside bait
stations in exposed locations. Glue boards lose their effectiveness in dusty
areas unless covered, and extremes of temperature also may affect the tackiness
of the adhesive.
Using Poison Baits (Rodenticides): Rodenticides
are poisons that kill rodents. They are available as either non anticoagulants
or as anticoagulants. The non-anticoagulants cause death either via the
nervous system or via the release of calcium into the bloodstream. Anticoagulants
cause death as a result of internal bleeding, which occurs as the animal's
blood loses its clotting ability and capillaries are destroyed. The active
ingredients 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 fed on for a number
of days. The exceptions are baits containing brodifacoum or bromadiolone.
These baits can cause death following a single feeding, although the mouse
does not die for several days.
When rodenticides are used, fresh bait must be 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 baiting situations.
Proper placement of baits and the distance between placements is important.
Space bait placements 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 to 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.
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 and factories. 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.
Predators Although cats, dogs, and other predators may kill mice, they do
not give effective control in most circumstances. It is not uncommon to
find rodents living 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. In barns, stables, and other areas where grain based feed is always
available to mice, some cats and dog breeds may help reduce mice populations.
