"The House Mouse" (Mus musculus)

Many of these animals carry a variety of viral, bacterial, and parasitic diseases . Mice associated with humans also have considerable economic impact through crop damage, destruction of trees, and food contamination.

Garlough and Spencer (1944) noted the word "mouse" can be traced to the Sanskrit word musha which is derived from a word "to steal." Mice were well known to the ancient Greeks and Romans and were featured prominently in their art and literature. This cosmopolitan rodent is believed to have come originally from Central Asia. It is now found throughout the world from the tropics to the Arctic and Antarctic.

Linnaeus originally named the house mouse Mus musculus. Later, taxonomists cosidered that two subspecies of house mice had been introduced from Europe into the New World: Mus musculus domesticus and M. m brevirostris. Especially in the Midwest these two forms came into contact and interbred. Taxonomic "splitters" came to recognize several hundred verieties.

In recent years opinions have been revised again, and you are likely to see Mus domesticus cited in technical papers. Some specialists now want to reserve M. musculus for those mice in Eastern Europe. However, continuing to use our present technology (i.e., M. musculus) seems to me the appropriate and least confusing course of action.

Life History Of The House Mouse. House mice are extremely prolific breeders. At 35 days of age they mature and carry embryos for 18 to 21 days. If a female aborts, she can become pregnant again within 48 hours. The average litter size is about six. Variations in genetics, food supply and temperatures affect these numbers. At low temperatures, mice produce fewer offspring, and they are smaller in size. A female suckles her young for about four weeks. The female may become pregnant following parturition or while still lactating. In such cases, the gestation period will be lengthened. Therefore, if all goes well, a female can have litters approximately every 40 to 50 days. Under optimum conditions (often found indoors) mice can breed throughout the year. Outdoors, mice are more seasonal breeders, peaking in the spring and fall.

Newborn mice are extremely small, blind, pink and naked, except for short vibrissae. They weigh between 0.02 and 0.03 ounces. After two weeks, the eyes and ears open, and the young mouse is fully covered with hair, makes short trips from the nest and begins feeding on solid food. At four months of age an adult mouse weighs about 25 grams, slightly less than 1 ounce. Eaton and Cabell (1949), on studying laboratory mice, state: "Young mice may be moved from their dam at three weeks of age and the dam rebred. A female is not usually productive after 15 months, but may live much longer. Male mice have been known to live as long as 2-1/2 to three years."

Garlough and Spencer (1944) note mice usually live for 15 to 18 months, and some have lived up to six years. However, considering their natural enemies and the diseases to which they are susceptible, it is generally agreed their life expectancy is less than a year.

Storer (1931), Orr (1944) and others have observed "community nests of mice" wherein several females may share the same nest with their accumulated brood. Orr observed as many as three females to use the same nest. Storer found one nest to harbor 36 young. "Of these one brood was newly born, another of a size ready to leave the nest, and remainder of intermediate development, with eyes still unopened." Under such crowded conditions, survival may be relatively low.

Feeding Patterns. Garlough and Spencer (1944) noted house mice "eat about the same kinds of food as do human beings, including meats, grains, cereals, seeds, fruits and vegetables. They prefer sweet liquids to pure water for drinking." According to Mills (1947), house mice feed 15 to 20 times a day, consuming 100 to 200 milligrams of food at each feeding. Ives (1948), speaking of the feeding habits of mice, says: "They do not sit down and eat a large amount of food at one sitting like a rat does. Instead, they duck in and out and dart around picking up a morsel of food here and there." The same author notes that four seeds suitably treated with a poison will kill a mouse, and a mouse will eat that many at one time.

While mice are nibblers and feed many times in many places, they have two main feeding periods. They eat at dusk and just before dawn, interspersed with many other feeding bursts approximately 3/4 to 1-1/4 hours apart. They have to consume about 10 to 15 percent their body weight every 24 hours. When water is available, they drink.

Southern and Laurie (1946), who studied the house mouse in grain stacks in the field, make the following notes about the water requirements of house mice: "Unlike rats, mice do not feed to forage outside a rick for water; in captivity they live in good health on a diet of wheat, which itself contains about 15 percent of water, though they will take a small amount more if it is provided. This is generally less than 1 ml per day, and this quantity would be easily obtained on the outside in the form of dew or rain. This probably accounts for most mice in a rick visiting outside, and for the readiness with which they take poison bait mixed with water."

Social Behavior. Women's liberation has a long way to go in the world of house mice. Each male mouse stakes out a territory and guards it. Within the territory can be several females and lower ranking males. While the dominant male is busy defending his territory, the female mice may be "getting acquainted" with lower ranking males. Female mice will often mate with more than one male. A mouse's territory depends upon a number of factors, including number of mice in the entire structure and arrangement of materials within the structure. The more mice present, the less territory each has. Some mice can remain in a desk or pallet for an entire lifetime, but it is important to keep in mind that the mouse is climbing up and down within the materials stored on the pallet or in the desk. Mice entering an already occupied territory are not welcome and are driven off. When mouse populations swell, the mice will seek out rodent bait stations, exposed window ledges and any other area where they can hide from other more aggressive mice.

Mice are cannibalistic and will feed on each other when hungry. Mice caught on glue boards may be partially eaten by other mice. Mice in multiple live traps will often be eaten by other mice caught in the same trap.

Because mice scurry from place to place and deposit fecal droppings wherever they please, the easiest way to determine if mice are present is to locate their droppings. Other signs include gnaw marks, small holes in walls and doors, and the pungent odor of their urine. The easiest way to discern active infestations is to sweep up the droppings and see if new ones appear the next day.

Emlen (1950) made a study of the diseases mice travel by capturing 1,572 mice, marking them and then releasing them at the point where they were caught. He found the average distance was 12 feet and that 90 percent moved less than 30 feet and 70 percent less than 10 feet. From this he concludes mice are "stay-at-homes" and do not move around unless disturbed. As a result of his studies, Emlen recommends the distribution of a large number of poison baits sparced no more than 20 feet apart. Southern and Laurie (1946) note the average range of mice in cellars is not more than 48 square feet in 24 hours.