Information About Mice
Mice (singular, mouse) are part of a mammalian family, are one of the more common pests to homes and coincidentally are also a very popular house pet. Generally just a nuisance pest, the mouse can be potentially harmful or dangerous under certain circumstances.
The mouse came to the United States from Europe along with the original settlers. Mice species are some of the more environmentally adaptable mammal species on the planet.
Contrary to popular belief, mice are actually very smart creatures. Mice are on the smaller end of the rodent size spectrum, are nocturnal, are rapid breeders and are known to be prey for cats, certain birds, snakes, wild dogs and foxes.
Classifications, Types & Anatomy
The mouse (plural, mice) is a mammal found in the Order Rodentia. There are numerous mouse species, but the most common species in the New York metro area are the House mouse, Mus musculus, and the White-footed mouse, Peromyscus leucopus.
The average mouse is around 2-4 inches in length, not including their tail, weighing around ½ an ounce. They are covered in fur, have poor eyesight (they are color blind) and keen hearing. Their sense of smell, touch and taste are all very well developed. They also have an extremely narrow thermoneutral zone, which means they are only comfortable in a specific, small range of temperature variances.
Mice have two lungs, but the lobes within these lungs are not evenly distributed. There is only one lobe present in the left lung but four lobes within the right lung. The stomach is also divided into two distinct sections – one section to digest the food, the other to store food for later. Female mice also have five pairs of mammary glands and nipples – making them easy to distinguish from the males who have none.
Mice have incisor teeth that continue to grow throughout their life. These teeth can get through most surfaces with relative ease. Additionally, mice are extremely flexible and can easily run through a hole the size of a dime, squeezing into spaces even half that size.
They have four legs, all of which are used while walking but when eating or fighting, they will sit on their hind two legs. The tail is always used for balance, whether walking or sitting. It is also useful in jumping, as mice can jump vertically about 20 inches. Their whiskers can be used to sense movements in the air. Their nose is useful in detecting pheromones produced by other mice in order to communicate with each other.
Young, immature mice, or ‘pups,’ are typically hairless and have closed eyes and ears. They are usually 1/20 of an ounce at birth with large ears and small black eyes. The eyes begin to open about 1-2 weeks after birth, but hair begins to grow within a few days. One can also distinguish the sex of the mouse, especially at birth before nipples develop, by comparing the distance between the mouse genetalia and the anus. Males will have a greater anogenital distance than females, regardless of age
The shape of their feces can also identify mice species, where most mouse droppings are blunt on one end and pointed on the other, other rodents may have two blunt ends or two pointed ends. Mouse droppings are often confused with American Cockroach droppings, which are blunt at both ends and are rigid.
The House mouse, Mus musculus, is usually light brown/black to gray in color. Their weight ranges from 0.4-0.9 ounces and are usually 1-4 inches long plus a 3-4 inch tail, which has almost no hair on it, just like the ears. Their droppings are black and generally have a musty odor associated with them.
The White-footed mouse, Peromyscus leucopus, unlike the house mouse, has a distinct line between the dark coated fur on the top of their body and the light colored hair on the bottom. Also, in contrast to the house mouse, the tail does have hair on it. Most of the hair on the body and tail are darker – brown or black, but the underbelly and feet are white. The white-footed mouse usually weighs around ½ - 1 ounce and measures approximately 7 inches long.
Lifecycle, Breeding & Feeding Habits
Mice are primarily nocturnal animals that feed on a variety of foods, but generally eat seeds and grains. Their poor eyesight is compensated by other keen senses, including hearing and smell, two senses which are highly relied upon when foraging for food in the dark.
Although they prefer “healthy” foods, mice will also feed on bacon, butter, chocolate and other sweets and fatty foods in addition to nuts and other organic substances. Mice also require a small amount of water each day and if there is no water present, they can survive by extracting water from the foods they eat.
In nature, mice are generally herbivores, but indoors, they are a lot freer with their diet, feeding on anything that will provide them with the proper nutrition including human food scraps. In some cases, mice may actually feed on their own droppings when there are no other food sources present. When they eat, they do not eat in large quantities, instead taking small bites or ‘nibbles,’ and coming back to the food source a number of times before becoming full. (Note: most mice, like most rodents, do not vomit.)
Mice are extremely rapid breeders, on average producing as few as 5 and as many as 10 litters in a one-year period. Females begin their reproductive cycle, estrus, approximately 25-50 days after birth, depending on the species. Usually, the female will detect a mating pheromone from a male and go into estrus in about 72 hours, at which point she is ready to mate. The estrus cycle typically lasts around 12 hours and occurs in the evening/night time as mating is also a nocturnal activity.
The gestation period lasts around 20 days. Litters will usually produce 6 pups in optimal environments. Females can be very hostile during parturition (labor and birth) and for 2 days postpartum.
When living outdoors, mice will tend not to reproduce in the colder months. If living in a sheltered setting, breeding will continue all year. The average life span of a mouse is 9-12 months.
The male House mouse will tend to offer more of a verbal cue or ultrasonic call in order to signal the female that he is ready to mate. The female tends not to respond even though she can produce the same noises. The estrus of the female house mouse can last up to six days. If house mouse females are housed together in close quarters it is possible that none of them will have estrus.
The White-footed mouse has an internal pocket in its cheek, like a squirrel, that will allow it to place food to be transported to ‘storage sites’ and saved for eating during colder months.
Females will tend to produce 2 to 6 pups per litter but can reproduce anywhere from 1-6, with 2 to 4 litters per year.
In the wild, the white-footed mouse may live up 2 to 3 years.
Environments & Activities
Generally nocturnal, mice are active at night but will sometimes be seen during the day. They have poor eyesight, but will use their other senses, which are very keen to help navigate from point to point and forage for food. Aside from hunting for food, mice activities are limited to hiding and escaping predators. They are very uncomfortable with unfamiliar surroundings and tend to hug the walls or corners.
Mice are also very territorial, especially the male of the species. Two males who are forced to live in close quarters will often turn hostile. If there is a male present in a nest, the other males will stay away from that territory and certainly not enter if the male is present. However, if the male is not present, the offending mouse may go in and try and feed or breed within the other male’s nest.
Mice, specifically House mice, will tend to invade homes when looking for shelter, warmth or food. They create their nests out of shredded paper or other similar materials. Mice are excellent at finding their ways into structures, buildings and homes in search of food. They will climb, swim, crawl or squeeze through cracks ¼ inch in diameter (half the size of a dime) or gnaw their way through impediments. They are very curious and will investigate and inspect every new object they encounter. Poor sanitation will attract these animals.
White-footed mice tend to inhabit wooded areas but they can be found nearly anywhere, including under and within buildings and other human structures.
Dangers & Effects On Humans
Although they mainly keep to themselves, are smaller than the size of most human hands and are generally harmless creatures, mice can pose threats to human health and property when they come into contact with us.
They have the ability to bite, spread diseases, destroy crops and be a general nuisance with, gnaw marks and musky, odors. . They can destroy entire fields of crops. Packages, books, electrical wiring, and other household items are typically the most affected by gnawing mice – especially the House mice – in some cases causing fires or power outages.
Mice throughout the world are known to spread over 35 diseases. Disease transmission can occur through biting or through the consumption of food contaminated by their urine or feces. The White-footed mouse can transmit Hanta Virus through their droppings or through urine. Diseases carried by mice may also be transmitted to humans through other carriers such as ticks or fleas that feed on an infected mouse and then a human or pet.
Some of the diseases carried by mice in the New York region are: Hantavirus Pulmonary Syndrome (HPS); Leptospirosis; Lymphocytic Chorio-meningitis (LCM); Rat-bite Fever; Salmonellosis; Tularemia.
Control & Treatment
The most important aspect of rodent control is locating the entry points into the home or workplace. Very often these areas are indicated by gnaw marks on the walls or stored food or by their droppings. In some cases you may even hear squeaking or running within the structure. Once the point of entry or even a nest has been identified, there are several treatment and control methods that can be utilized:
Place traps and other control tools in areas with high mouse activity
Seal all holes, cracks and crevices bigger than ¼ inch in diameter with cement, metal and/or copper mesh
Maintain good sanitation inside and outside the premises
Doors and windows and window screens should all be in place and fit tightly
Plastic, rubber, foam, wood and other objects that can be gnawed through will not provide sufficient protection from rodents.
NOTE: Poisons and rodenticides may be effective in certain situations but will not provide long-term relief and should always be used in conjunction with other exclusion and control efforts and with the guidance of a pest control expert.