Our old housecat, Betty, has a pretty easy life. Getting on in years, she spends the bulk of her days sleeping at the foot of our bed on her own cushiony pillow, one of those designed especially for pampered pets. It's getting hard for her to leap up high in her old age and portly condition, yet she still manages somehow to hop and claw her way up there. I'm starting to wonder how long I should make her exert herself like that, knowing as I do that it's her favorite place to sleep. But since toys and play don't interest her anymore, it's about the only real exercise she ever gets. She jumps down every now and then to pad into the kitchen to her food bowl, always knowing when it's time to eat. Her internal clock is so accurate, you'd think a dinner whistle blew! Then it's on to the litter box when nature calls, and back to her cushy bed. That's pretty much her daily routine.
A couple of weeks ago, I noticed that Betty was uncharacteristically spending a lot of time in the kitchen at night, just sitting motionless in the dark and staring intently at the same place under the dishwasher. Every once in a while her head would jerk to the right or left, but her feet stayed planted as her eyes, wide open, continued to focus on some unseen object in the darkness. It didn't take a genius to figure out that something was rustling around back there, and it had her undivided attention. Betty's sentry duty reminds us that it's time for that annual winter ritual, when the onset of cold weather causes enterprising little creatures called "mice" to move into manmade structures in search of food and shelter. One can't blame them really -- after all, it's cold out there! The problem is, they weren't invited, and left unchecked they can become quite the troublesome little pests. There really is no choice but to engage in that long-suffering American custom, that age-old battle of human versus mouse!
Mus musculus -- the house mouse.
The familiar house mouse is a small, slender rodent with a pointed snout; small, somewhat protruding black eyes; relatively large, nearly hairless ears; and a naked, scaly tail that is about as long as its body. Almost everyone has seen one at one time or another, and many of us have had the dubious distinction of actually matching wits with them in our homes and outbuildings. This species of mouse is generally grayish brown or gray with light gray or buffy underparts. It also has a musky odor produced by its anal glands, quite distinctive and a definite tell-tale sign. Native to central Asia, house mice accompanied the first Europeans to the New World on ships. They have since spread across North America and now occupy every state, including the coastal areas of Alaska. Since these mice are adapted to a diet consisting largely of seeds and grain, agricultural practices through the years have proceeded to sweep mice right up to humanity's front door. The association between house mice and humans has become so intimate that today they are often described by the term "commensal," which literally means "sharing the table."
House mice are prolific breeders, and have a gestation period of 19-21 days. In nature, their young are born from early spring until late autumn, but indoor mice may continue to breed throughout the winter. Nests are constructed of shredded paper, cloth, insulation, or similar materials in walls, floors, drawers, cabinets, boxes, furniture, or other secluded spots. Outdoor mice occupy nests of grass placed in burrows or hidden under rocks or logs. Litters usually contain 5-7 altricial (hairless and helpless) pups, but 8-10 per litter are not uncommon. Their eyes and ears open at about 2 weeks of age, and they begin to make short excursions from the nest and eat solid food at 3 weeks. Weaning follows soon after. Amazingly, the females reach sexual maturity as early as 6 weeks of age, and so a healthy mature female may have 5 to 10 litters per year. Small wonder that under favorable conditions, house mice populations sometimes seem to explode! This potential, though, is partially alleviated by the tendency of house mice to be short-lived. While captive mice can sometimes live up to six years, about one year is the longest a free-living mouse can expect to survive.
House mice are mainly nocturnal (active at night) and have poor eyesight, relying on their hearing and excellent senses of smell, taste, and touch. Considered to be the "acrobats" of the rodent world, they have physical capabilities that enable them to gain entry to structures by gnawing, climbing, jumping, and swimming. Mice constantly explore and learn about their environment, memorizing the locations of pathways, obstacles, shelter, food and water. They quickly detect new objects in their surroundings, yet do not generally fear them. This characteristic causes them to enter bait stations and sample the foods (baits) set in traps, enabling humans to be successful in extermination efforts. When inside, the lives of mice are spent in secure, comfortable places inside walls, in pantries, and under and behind cabinets and appliances. The entire area occupied by an indoor mouse during its lifetime may be less than the size of an average room. In fact, when food is plentiful indoor mice may never wander more than a few yards from their nests. They climb and jump well, but generally prefer to run along walls rather than crossing open spaces. And unfortunately for us, they can squeeze through holes just over 1/4 inch in diameter. Obviously, it's a challenge to keep them out!
While they prefer seeds and grains, house mice will eat new foods and are considered "nibblers," sampling whatever food they find in their environment. They prefer those high in fat, protein, or sugar such as bacon, chocolate candies, butter, and nutmeats, even when seeds and grain are available. Just about anything in our cupboards, drawers, pantries, or on our counters is fair game for eating, gnawing, or nesting materials. They can survive with little or no free water, obtaining moisture from the food they eat, but will readily drink when water is available.
When house mice inhabit our homes, storage areas, farms, and warehouses, they almost always cause some degree of economic harm. They can cause structural damage with their incessant gnawing activities and usually contaminate food and living areas with their urine, droppings, and hair. So how do we know when we have a problem, and what can we do to protect our food and belongings from these unwelcome guests? In next month's column, we will examine some sure signs to look for and explore a few workable solutions for ridding our surroundings of these irritating and diminutive but worthy opponents. And as for the mouse in my kitchen, did Betty eventually earn her keep? Tune in next month and find out.