House mice are small rodents with relatively large ears and small black eyes. They weigh about 1/2 ounce and usually are light brownish to gray in color. An adult is about 5-1/2 to 7-1/2 inches long, including the 3- to 4-inch tail.

Droppings, fresh gnaw marks, and tracks indicate areas where mice are active. Mouse nests are made from fine shredded paper or other fibrous material, usually in sheltered locations. House mice have a characteristic musky odor that identifies their presence. Mice are active mostly at night, but they can be seen occasionally during daylight hours.

Biology: Native to Central Asia, the house mouse arrived in North America on ships with settlers from Europe and other points of origin. A very adaptable animal, the house mouse often lives in close association with humans along with Norway Rats and Roof Rats; however, mice are more common and more difficult to control than rats. Although house mice usually prefer to eat cereal grains, they are "nibblers" and will sample many different foods.

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 to 12 inches from the floor onto a flat surface. Mice can squeeze through openings slightly larger than 1/4 inch across.

In a single year, a female may have 5 to 10 litters of about 5 or 6 young. Young are born 19 to 21 days after mating, and they reach reproductive maturity in 6 to 10 weeks. The life span of a mouse is probably 9 to 12 months.

Control: Effective control involves sanitation, exclusion, and population reduction. Sanitation and exclusion are preventive measures. When a mouse infestation already exists, some form of population reduction such as trapping or baiting is almost always necessary.

To devise the best control program for a particular situation, always begin by removing or limiting the mouse's food source and shelter whenever possible. Trapping works well when mice are not numerous, or it can be used as a follow-up measure following a baiting program. When considering a baiting program, decide if the presence of dead mice will cause an odor or sanitation problem. If so, trapping may be the best approach. Removal of mice should be followed by taking steps to exclude them so that the problem does not reoccur.

Because mice can survive in very small areas with limited amounts of food and shelter, their control can be very challenging, especially in and around older structures. Most buildings in which food is stored, handled, or used will support house mice if the mice are not excluded, no matter how good the sanitation. While good sanitation will seldom completely control mice, poor sanitation is sure to attract them and will permit them to thrive in greater numbers. Pay particular attention to eliminating places where mice can find shelter. If they have few places to hide, rest, or build nests and rear their young, they cannot survive in large numbers.

Exclusion is the most successful and permanent form of house mouse control. "Build them out" by eliminating all gaps and openings larger than 1/4 inch, through which mice will enter a structure. Steel wool makes a good temporary plug. Seal cracks in building foundations and around openings for water pipes, vents, and utility cables with metal or concrete. Doors, windows, and screens should fit tightly. It may be necessary to cover the edges of doors and windows with metal to prevent gnawing. Plastic screening, rubber or vinyl, wood, and other gnawable materials are unsuitable for plugging holes used by mice.

Simple, inexpensive, wood-based snap traps are effective and can be purchased in most hardware and grocery stores. Traps can be baited with a variety of foods; peanut butter is the most popular because it is easy to use and very attractive to mice. Set the triggers lightly so the traps will spring easily.

Multiple-capture live traps for mice, such as the Victor Tin Cat and the Ketch-All, also are available from hardware stores and pest control suppliers. They can catch several mice at a time without being reset so labor requirements are reduced.

Set traps behind objects, in dark corners, and in places where there is evidence of mouse activity. Place them close to walls so mice will pass directly over the trigger. Traps can be set on ledges, on top of pallets of stored materials, or in any other locations where mice are active. Use enough traps to make the trapping period 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 that are attempting to cross them, in much the same way flypaper catches flies. They are available at many places where other rodent control products are sold. Place glue boards along walls where mice travel. Do not use them where children, pets, or desirable wildlife can contact them. Nontarget animals that become caught on the glue board can be removed in most cases by using vegetable oil as a solvent to loosen the glue. Glue boards lose their effectiveness in dusty areas unless covered. Extreme temperatures also may affect the tackiness of glue boards.

Baits to control rodents are formulated with an attractant (generally food) and a rodenticide (toxin). Most rodenticides used to control mice around the home are already mixed with an attractant in commercially ready-to-use baits. The rodenticides in these baits are either anticoagulants or other rodenticides such as single-dose toxicants and chronic rodenticides.

Habits: The Norway, or brown, rat lives both as a commensal in close association with man and in the feral state, chiefly where vegetation is tall and rank and affords adequate protection. As a commensal this rat lives principally in basements, on the ground floor, or in burrows under sidewalks or outbuildings. Although more at home on the ground, these rats are adept at climbing and have been observed traveling along telephone wires from one building to another. In places they become exceedingly numerous and destructive.

They feed on a variety of items including both plant and animal materials. All sorts of garbage appear to be welcome, but their main stay is plant material. Grains of various sorts are highly prized. When established around poultry houses, they feed extensively on eggs and young chickens. They even have been known to kill lambs and young pigs!

These rats are prolific breeders. The gestation period varies from 21 to 23 days and the number of young from two to 14, averaging seven or eight. At birth they are blind, naked, and helpless. They grow rapidly; their eyes open in 14-17 days and they are weaned when 3 or 4 weeks old. There is no delimited breeding season, but there is a tendency for a slow-up in reproduction during fall and winter. The life span is reported to be 2-3 years.

Control: The best way to eliminate rodent problems is through exclusion. Discourage rodents from establishing outside: keep your yard free of debris; trim back vegetation from around the structure and roof; keep bird feeders away from the structure; regularly clean spilled bird feed. Block access to your structure: check that crawl space doors fit tightly and are in good condition; check that the vents are in tact; repair access points in the foundation and roof.

Biology: The Roof Rat is an “arboreal” animal, preferring to live above ground level in trees, although it has adapted well to upper areas of structures as well, living in attics and traveling by means of wires and cables attached to homes. It is nocturnal and secretive, staying out of view within the foliage provided in landscaped environments, and feeding heavily on the fruits, nuts, vegetables, or garden snails found there. Like the Norway Rat is also is shy about new objects in its familiar environment, and may avoid control measures such as traps or bait stations. A normal life expectancy for them is one year or less, ranging from 5 to 18 months. The gestation period of the female is 22 days, litters average 8 to 9 pups, and she may have 3 to 4 litters in her one year, being somewhat less prolific than the Norway Rat. Peaks in breeding occur in the spring and the fall. Problems from Roof Rats include the potential for disease, such as plague, spread by their fleas. They are extremely destructive to stored food products in structures, crops in residential areas, and cause tremendous damage due to their gnawing on structural members, pipes, and electrical wires.

Control: Exclusion from structures is of high importance in preventing entry and damage from this rat. They can enter through any opening wider than one half inch, swim well, and can climb any rough surface, along wires and cables, and can jump vertically about 3 feet. Glue trays work very well for Roof Rats, along with snap traps placed in runways and bait stations using various formulations. Like the other domestic rodents they prefer to remain against vertical surfaces, in contact with their “guard hairs” on their body, and control measures should be placed against these pathways.

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