Jennifer Schultz Nelson
Extension Educator, Horticulture
Although the topic of mice is really not a horticultural topic, or exists at the far fringes of horticulture at best, this time of year our office gets calls about mice. Fall is the time of year mice are looking for a warm place to spend the winter. This is especially true if you live anywhere remotely rural. Even a park can be a source of mice.
There are a few animals that for lack of a better description completely creep me out. Mice are one of them. Just researching the information to write this column makes my skin crawl. The idea for this column unfortunately came from recent personal experiences.
My husband and I live near both woods and farm fields. I expected to see the occasional mouse in the garden and even the garage. And we did. I saw a mouse once or twice in the garage, put out a trap and caught it. We were certain that what we caught in the garage were mice, as opposed to voles, which are a problem in our garden each winter. Mice have relatively large ears and tails about the length of the body. Voles have relatively small ears, and stubby tails.
We have traps and poison baits strategically placed around the garage in places that might be attractive to a mouse. We have all our food sources, like bird seed and grass seed, in sealed heavy plastic containers. I figured this was all I would have to do. As it turns out, mice are determined little creatures.
Earlier this summer, I opened the closet in our garage to change the furnace filters, and let out a shriek. There was evidence that mice had been there. Mouse droppings were all around, and there were shreds of old carpet and insulation from a pipe that leads from our air conditioner.
The mice had apparently gotten in from our crawl space by gnawing through the insulation on the air conditioner pipe which gave them enough space to slip into the closet that holds our furnace.
Mice only need a ¼" gap to be able to squeeze through. One method of controlling mice in homes, garages and sheds is to "build them out" by sealing off any gaps that might allow them to enter. It is crucial to use materials that mice cannot gnaw through. They have strong incisors that make most plastic, wood and rubber unsuitable for plugging gaps.
Steel wool mixed with caulking is a good plug for gaps that cannot be sealed with metal or concrete. I mixed steel wool with caulk used for repairing concrete that has sand in it to plug the hole around the pipe near our furnace. So far it has worked.
Preventing mice from entering a building and trapping are the most effective ways to control them. When trapping or setting out poison baits, place them in places where mice travel, usually along the edge of a wall or other structure.
Mice do not travel far from shelter and food. They also tend to travel with one side of their body touching a wall or other structure. This wall-seeking behavior is called thigmotaxis by animal behaviorists. It may be related to staying safe from predators.
We use some traps in our garage, as one of the drawbacks for using traps is you have to check them and dispose of the dead mouse.
Another option, though not as effective are the many different forms of poison baits available for mouse control. Poison baits available to homeowners are usually anticoagulants, which prevents the mouse's blood from clotting after ingestion. These products are typically formulated with a low dose of poison in the bait so that the mouse feeds repeatedly and does not avoid the bait because of odd taste or onset of illness.
A big drawback of poison baits is that when the mouse dies, you have no control of where it dies. I learned about this the hard way too.
There is a closet immediately adjacent to the door leading from our house to the garage. One recent chilly Friday morning I opened the closet to grab a jacket, and noticed a horrible smell. My husband smelled it too. Further investigation revealed a dead mouse in the bottom of the closet. I was horrified. How in the world did it get there?
There were no holes in the closet or anywhere nearby that could have let a mouse in. It probably came in through the door, but how since there is a big step outside that door? It was surprising to me to read that mice can jump up to 13 inches from the floor to a flat surface, and can climb vertically over a rough surface. That big step was nothing to that little mouse.
As horrified as I was to find a mouse in our house, mice have invaded human dwellings for thousands of years. Mice thrived in early human agrarian settlements, as there was a ready food source from early human farms. Researchers have used mouse populations to document early human migrations. The mice went where the people went.
We will continue to refine our mouse excluding efforts this winter and hope that the word gets out in the mouse world that they are unwelcome at our house.