I thought I’d escaped the annual fall invasion of the house mouse (Mus musculus) this year. Then suddenly, in mid-November, I heard the pitter-patter of mouse feet in the attic and rustlings in closets, and started finding poop trails on the kitchen counters.
Could the mice have been breeding silently in the walls, or did whole families show up at once looking for winter digs? I know this species is an invasive, non-native pest and getting rid of them likely helps the environment, but I usually use live traps anyway. I just don’t like killing animals.
To ensure live-trapped mice won’t come back to where they were caught, they should be released more than a mile away (which I admit I rarely do but still have success in getting rid of them). A live trap can still stress mice and cause them to be disoriented when released, making them vulnerable to predation by a host of predators, but at least I’m putting them back into the food chain.
I found it interesting that one university agricultural-extension suggested live traps were cruel, while blithely recommending glue traps, which to me are incredibly so. They are also generally only effective in catching juvenile mice, leaving adults to continue to breed. Poison traps, which the site also recommended, aren’t much kinder and require careful disposal of the carcasses to avoid putting pesticides back into the food chain.
When I do try the lethal route, I stick to spring-loaded traps, which are generally considered the least cruel and most effective as well as safest to humans and the food chain. However, I have not had good results with these traps. Either my mice are incredibly clever or the traps don’t work that well, especially for adult mice, which seem to be able to retrieve the bait – even springing the trap – without getting caught.
In cruising around several science-based websites for more information on M. musculus, I found lots of interesting factoids about this species.
Although they predate humans, house mice are generally not great at competing with other rodents in the wild and are rarely found far from human habitat. While they can live for up to 20 months outside, most don’t survive longer than three months because of high predation.
Male mice are called “bucks”; females, “does”; young, “kittens” or “pinkies”; and a group of mice is (aptly) referred to as a “mischief.” House mice can be distinguished from native deer mice by their larger ears and naked tail.
Nocturnal, house mice are near-sighted and can only focus on items up to about two feet away, but can detect movement up to 45 feet away. They may see some colors, but not red. To maneuver in darkness, they rely to a great extent on their heightened sense of smell, as well as on whiskers and guard hairs to feel their way through tight places. They can hear noise in the ultrasonic range, well beyond human capacity.
House mice tend to keep to the same path in their nightly ramblings and rarely travel more than 50 feet from food sources. Mouse nesting complexes can vary from a short tunnel with just one chamber to a network of tunnels with several exits and chambers.
Although house mice live in colonies, they can be aggressive with each other. Females excrete a hormone in their urine that diminishes aggression toward them.
Though they generally spend the warm season outside, by fall, house mice head indoors for the winter, seeking nesting sites near warm places, such as refrigerators, ovens and water heaters. They shred paper, cardboard, cloth and other fibrous substances for nesting materials.
Prolific breeders, females pop out 15 to more than 150 kittens annually. Gestation is 18 to 21 days, and the female can become pregnant within 48 hours of giving birth. Young are independent after three weeks and reach reproductive maturity in six to 10 weeks.
House mice can contaminate food by spreading disease, such as salmonellosis (food poisoning), but are not considered serious disease vectors. The mouse’s dead skin flakes, fur, urine and feces have been linked to asthma attacks in sensitive individuals. This species can also transmit parasites, such as mites, tapeworm, ringworm and ticks, to pets and humans. Each day the typical house mouse leaves trails of 50 to 75 fecal pellets and several thousand “micro droplets” of urine. The latter fluoresce and can be viewed with a black light.
House mice tend to graze, taking a few bites of a food before moving on. They will eat almost anything, even soap and glue, but prefer cereal grains, along with vegetables, fruits and insects. Contrary to common belief, they are not fond of cheese, which is bad for them.
Typical among rodents, the teeth of the house mouse continue to grow throughout its life, so it’s imperative that mice continually gnaw to keep them from getting too long. Non-food items can be targeted, including wiring and other substances of comparable hardness.
House mice are athletic, able to jump vertically to a height of about 12 inches, across a gap of three feet and down 12 feet without injury. They can enter a hole that is as small as one-quarter inch – about the width of the average pencil – gaining access through small openings around utilities and dryer vents. They are great climbers, aided by scales on their tails and can easily go up shrubs and trees, wood siding, brick, sheet metal and utility cables to gain access to structures through openings in and under roofs. They also swim well and are not afraid of water.
Last, but definitely not least, house mice, along with other mouse and rat species, apparently sing. According to a 2011 article in the Smithsonian magazine (smithsonianmag.com), research by animal behavior ecologist Matina Kalcounis-Rueppell (University of North Carolina, Greensboro) has confirmed anecdotal stories going back at least to the early part of the 20th century about this phenomenon. Using sophisticated sound-analysis equipment, she and other researchers have found that mice can have several songs in their repertoire, some of which communicate their gender and species.