December 2016: Protecting Your Home from a Deer Mouse Invasion
By: Levi Price and Nicki Frey
Winter is coming and with falling temperatures we’ll be spending more time in our warm homes. Animals also like to stay warm during the winter so you may notice more wildlife trying to enter your homes and buildings. Deer mice (Peromyscus maniculatus.), the most common mouse species in southern Utah, can pose a problem when they create nests in outbuildings, sheds, garages, and our homes. This month we will be discussing some of the abilities of house mice and how to control them.
Deer mice, or field micee, as they are sometimes called, are common rodents throughout North America. Their head and body are about 3” long and their tail is also about 3” long. They have dark fur on their backs and whitish bellies. They have furred tailed, that are also dark on top and light on the bottom (bi-colored). As their name implies, they are native to fields and forests, but come into yards and homes that live close to these habitat types. They are uncommon in urban and suburban areas, where it is more common to encounter the non-native House Mouse (Mus musculus). They will eat many different types of food. Deer mice require little to no water as they absorb their water from the food they eat – small invertebrates, seeds, berries and nuts. They are usually nocturnal, but can occasionally be found moving about during the day. They are capable of breeding year-round and a female can have five to ten litters per year. Each litter usually has five or six mice in it. Young mice can start reproducing as soon as six weeks after birth. As you might imagine, their populations can grow rapidly under the right conditions. These traits alone make mice an extremely tenacious pest.
Mice are also capable of many physical feats that make excluding them from buildings extremely difficult. They can:
- Enter openings that are ¼” wide.
- Vertically jump up to 18”
- Climb almost any rough vertical surface including: wood, brick, concrete, weathered sheet metal, and many plastics
- Crawl through pipes and tunnels
- Gnaw through a wide variety of materials including low quality concrete, window screens, wood, and aluminum sheeting.
Dealing with mice often involves three steps: Prevention, Sanitation, and Trapping. It is far easier to prevent an infestation than it is to remove one. Once an infestation occurs a combination of all three efforts is usually required to remove them.
Mice enter building through a variety of ways. This make closing all of the entry points a tedious task. These are a few common places mice will enter through.
- Gaps at the bottom or sides of poorly sealed doors
- Holes around water pipes and electrical conduits
- Cold air return ducts on forced air furnaces; especially if it is located outside of the main house
- Climbing under and around poor-fitting garage doors
- Furnace ducts
- Laundry drains
- Roof vents and chimneys
- Sewer vents
- Any crack or hole in your house ¼” or larger.
- To prevent mice from gaining access to these areas follow these steps:
- Check the entire exterior of your house for any holes or gaps ¼” or larger. Pay special attention to areas around doors, vents, and utility pipes.
- Seal all holes and gaps with a rodent-proof sealant such as:
- 2" thick reinforced concrete
- 3" think non-reinforced concrete
- 24 gauge galvanized sheet metal
- 3 3/4" brick with joints filled with mortar
- 24-gauge, 1/4" mesh wire screen
- 22 gauge aluminum sheeting
- Cover all vents with thick metal screening.
- Ensure that all exterior doors fit tightly when closed.
Sanitation alone will not control mice because they can survive off of minimal amounts of food. But it will inhibit them and make it easier to detect their presence. House and yard maintenance will provide a good deterrent to rodent activity. The following activities are especially important for garages, barns and other outbuildings that do not experience regular daily human activity.
- Store all foods (including pet food) in rodent proof containers.
- Remove crumbs from the counters and floors.
- If you are storing large amounts of food don’t place it in direct contact with walls.
- Remove debris from around your house and property.
- Control weeds along the walls of your house.
IMPORTANT: When cleaning an area that has been invaded by mice, wear a “painter’s mask” to avoid inhaling fecal material (dust) that may have been infected with Hantavirus. Please see [http://www.cdc.gov/hantavirus/] for more information about human safety around areas infested with deer mice.
Trapping is an effective way to get rid of a mouse infestation. You can choose to poison the mice or use a trap. Poisoning mice is less labor intensive than trapping, but the mice may die in the walls of the home causing an odor problem. Poisoning also relies on poison which could cause harm if ingested. Trapping allows you to remove the mice from your home and does not rely on poisonous material.
- Poison mice with an approved anti-coagulant rodenticide.
- Trap mice with a spring trap, glue trap, or multiple catch mouse traps.
Baker, R. O., Bodman, G. R., and R. M. Timm. 2005. Rodent-proof construction and exclusion methods. In Hyngstrom, S. E., Timm, R. M. and Larson, G. E. (eds). 2004. Prevention and control of wildlife damage. Retrieved from http://icwdm.org/handbook/rodents/rodentexclusion.asp
Timm, R. M., and Howard, W. E. 2005. White-footed and Deer Mice. In Hyngstrom, S. E., Timm, R. M. and Larson, G. E. (eds). 2004. Prevention and control of wildlife damage. Retrieved from http://icwdm.org/handbook/rodents/whitefooteddeermouse.asp