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Mice

There’s a Mouse in My House!

By Jason O'Brien
Interim ISU Extension Wildlife Specialist


Fall is upon us and now is the time when homeowners will notice mice moving in for a winter visit. Two species of mice native to Iowa are seasonal visitors to homes in which they can gain access. 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 without the seasonal migration. Requiring enough space to fit their head through, about ¼ 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, which they survive on for portions of the winter.

Gap around central air pipe that can allow rodent entryExclusion is the preferred method of avoiding the seasonal visits of Deer and White-footed mice. Look for gaps in siding 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 where 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, it is recommended to tightly pack steel wool into the gaps first, and then apply the foam. Metal flashing will also create a chew-resistant barrier over openings. Other kinds of repairs may be necessary, depending on the location.

Trapping is necessary to remove the mice that are already inside. Several varieties of traps are available, including the snap trap and the box trap. The snap trap, such as the Victor® EasySet, is a kill trap and can be baited with peanut butter or moistened rolled oats. Mice travel along the edges of and behind objects, taking advantage of the protection and cover this provides. Set traps against walls, along likely travel routes, and behind objects where you have seen or suspect mice. Their droppings provide a clue to where they have been. You can improve your chances of catching mice by setting multiple traps in different locations. Consider setting two together with the bait sides opposite each other. The box trap is a live trap, which includes the Victor® Live Catch and the Victor® Tin Cat Repeating Mouse Trap. The latter is ideal if you have more than one mouse in the house. This trap has two chambers, one where the mouse enters and one where the mouse goes when it is caught. The trap is designed to automatically reset itself so that multiple mice can be caught at once. The trap works without bait and relies on the natural curiosity of mice. Again, these traps should also be set against walls and along likely travel routes. Mice can be released outside, but complete repairs so these same mice do not return.

Keep in mind this additional information. First, properly store grains and other seeds in rodent-proof metal containers and avoid leaving food out over night. Second, 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 order problems. Also, glue traps, while effective at catching mice, are also not recommended, as this is generally messier and subjects the mice to a slow death due to starvation and injury. Finally, ultrasonic devises labeled as rodent repellants do not live up to company claims and independent research has not shown they are effective at rodent control.

Note: Reference to the Victor® brand is not an endorsement, and is used here as a way to illustrate the kinds of methods available to clients.

Photo Credit: photo by Stephen Vantassel © Internet Center for Wildlife Damage Management, http://icwdm.org