By Jason O'Brien

Interim ISU Extension Wildlife Specialist

Iowa State University Extension

Now is the time when homeowners will notice mice moving in for a winter visit. Two species of mice native to Iowa can be seasonal visitors in homes. The deer mouse (Peromyscus maniculatus) and white-footed mouse (Peromyscus leucopus) make their way into homes in search of winter shelter after having spent the spring and summer outdoors raising young and foraging. The house mouse (Mus musculus), on the other hand, will live year-round in your home.

Requiring only enough space to fit their head through, about one-fourth inch or larger, both Peromyscus species will bring in nesting material or create their own inside, chewing apart paper, insulation, foam and any other material deemed suitable for a cozy nest. These mice also begin stashing food, such as corn kernels and bird seed, on which they survive for portions of the winter.

Exclusion is the preferred method of avoiding the seasonal visits of deer and white-footed mice. Look for gaps where the siding meets the foundation or where pipes and other utilities enter. Cracks in foundations and loose-fitting doors without proper weather stripping are other obvious places mice can get in. And, because mice are good climbers, don’t forget to check for poorly-fitted windows and disrepair around the roof, including attic vents. Mice can easily travel within walls, and without a way into the living quarters, you may never notice them. Repairs to exterior openings are necessary to avoid costly damage to wiring and other fixtures of your house.

Rodent-proofing can be as simple as adding or replacing weather stripping on doors and windows, which will reduce your heating costs, to filling cracks and holes with an expanding foam sealant. Because mice are chewers, tightly pack steel wool into the gaps first, and then apply the foam. Metal flashing will also create a chew-resistant barrier over openings. 

Trapping those already inside

Trapping is necessary to remove the mice that are already inside. Two common types of traps, the snap and box traps, work effectively. The snap trap is a kill trap and can be baited with peanut butter or moistened rolled oats. Mice travel along the edges of and behind objects, where they are less visible. Set traps directly against walls in these areas. Mouse droppings indicate where they are active.

To improve your chances of catching mice, set multiple traps in different locations, where you see the most activity. Box traps vary in design and all are live traps, for those who prefer not to kill the offending critters. They work without bait, relying on the mouse’s natural curiosity. If you have many mice, consider the multiple-catch box traps. This trap has two chambers, one where the mice enter and one where they go when caught. The trap operates by winding it up and automatically resets itself so that multiple mice can be caught without resetting. Set these traps in the same locations described above. Live-trapped mice can be released outside, but complete repairs first so they do not return.

For additional protection, properly store grains and other seeds in rodent-proof metal containers and avoid leaving food out over night. ISU Wildlife Extension does not recommend poisons as an initial solution unless all other methods have been unsuccessful. Use of poisons can be a risk to pets and children and often means mice die in inaccessible places, which can cause odor problems. Glue traps, while effective at catching mice, are not recommended, as they are generally messier and subject the mice to a slow death due to starvation and injury. Ultrasonic devices labeled as rodent repellants do not live up to company claims and independent research has not shown they are effective at rodent control.

This article is from the December 2008 issue of Acreage Living. Other articles in this month’s issue--

• Add Window Layers to Save Money
• Winter Power Outages

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