In last week’s column, I told you about several annoying invasion experiences I had with the deer mouse, Peromyscus maniculatus gracilis, commonly found in our northern Lake States. My close encounters with this mouse, and those of many others this year, prompted me to find out more about this little rascal. Here is what I found out.
The deer mouse is a nocturnal mouse that likes to live in the woodlands, both coniferous and mixed deciduous and coniferous, but also likes grassy, shrubby habitats too. It is partially arboreal and has a long, bi-colored tail and sharp toe nails adapted for climbing. I have seen them climb up and down eight-foot wooden posts to get into and out of my bird nesting boxes with no problem. I wouldn’t have believed it until I saw it with my own eyes. They like to nest in my bird boxes, but they also will nest in trees, on the ground, under logs and roots, or in hollowed out stumps, or in drawers, cabinets, and attics in buildings.
Their nests are made of leaves, grasses, and other plant materials, but they love to make them out of insulation when they get into buildings. Their breeding season is generally April to August but, if food and warmth are available, they will tend to breed all year long. Males are promiscuous, opportunistic breeders. Litters range from one to 11, averaging four to six after a gestation period of 25 to 27 days. The young are weaned when about 30 days old. One female may have up to five litters a year. Adults usually live about one year (but not at my place), but in captivity can live up to eight years. They do make pretty good pets!
Because this mouse is so prolific, it may be the most common mammal in some woodlands in terms of numbers. Its populations seem to decrease substantially every four years or so and then rebound back up to peak numbers which may have happened this year as they are EVERYWHERE. Just ask anybody if they have had mouse problems this year. All those who have, raise your hands. I see hands going up all over our Northwoods.
The food of this woodland deer mouse consists of over 50 different food items including various seeds. They like my sunflower seeds, small nuts and fruits, and a considerable number of insects, many of which are in the larval or chrysalis stage, and invertebrates. They often are a nuisance to farmers because they like to eat small grains like wheat, soybean, corn, and sorghum. They will store food for future use like they did sunflower seeds on my car cabin filter and in the drawers of our garage workroom. The mice rarely drink water in the wild, meeting their water needs from dew and the water in their food.
The deer mouse is one of the most studied of all American small mammals because it is so common and wildly distributed. For the same reasons, it is a staple food for many raptors, small carnivores, and snakes. However, sometimes the deer mouse population ‘explodes’ to such an extent that predators are overwhelmed and can’t keep up with controlling them. That is why every few years we get an invasion of deer mice in our homes and outbuildings. If you have mice where you don’t want them, here is what you can do based upon some expert professional pest control advice.
The key to keeping any mouse species out of a structure is to identify the species of mouse causing the problem and target controls to its specific behavior. Also, sanitation, harborage elimination, and structure access point reduction are necessary. If a lot of mice are already in an occupied structure, I recommend getting professional pest management help.
Exclusion is the best preventative control method. Seal all potential entry holes with 1/8-inch mesh hardware cloth, copper gauze, or silicone caulk. Store bird seed and dry pet foods in areas other than the garage or storage sheds unless kept in metal, tightly covered cans. I remember reaching down into a can of uncovered sunflowers seeds once only to have a mouse scurry over my hand! A good mouse trap baited with peanut butter is irresistible to mice!
And most important, deer mice can be vectors and carriers of emerging infectious diseases such as hantaviruses and Lyme disease. If you discover nests or dead deer mice near you, you must handle them with care. When interacting with deer mice bodies, nesting materials, or waste in any capacity one should wear a respirator with a HEPA filter and plastic gloves. Pick up a dead mouse in a reversible plastic bag and dispose of it in the garbage.