Are mice eyeing your house as a winter retreat?  

By Robert Durgy, UCONN EDUCATION CENTER  

When the weather gets cold we at the Home and Garden Education Center get numerous calls about unwanted visitors entering people's houses. Fall is the time when mice, squirrels, even flying squirrels make their way indoors to find shelter for the winter. And as cute as these fuzzy little creatures are, they might bring with them other unwanted pests like ticks, fleas or lice.

The two most common types of mice are the house mouse (Mus musculus) and the white-footed mouse (Peromyscus spp.). In fact, there are several species in this genus that are often called white-footed mice. The two most common are the P. leucopus and P. maniculatus. These mice are found throughout the United States.

The house mouse can be found in homes, barns and commercial buildings, but also in open fields and agricultural land. They usually are found close by a human population, but not always. When house mice are residing in your home, they are usually there all year long. White-footed mice are more likely to be found outside. They occupy any type of environment that will offer protection and food. Fall is usually when you'll find them entering your house.

Both types of mice feed mainly on seeds and nuts but will try just about anything. Mice have a tendency to sample only small amounts of food while foraging. Then they will return to the food that suits them best. Food high in fat or protein such as butter, cookies and discarded portions of meat will often pique their interest.

Very little water is necessary for their survival as long as the food they eat has some moisture in it. Food is often cached in hidden locations and can be an indication that a nest is nearby.

Mice are nocturnal so you will most likely be alerted to their presence by gnawed wood or plastic, opened food containers and droppings. Breeding primarily takes place during spring and fall, consisting of six or more litters per female per year. So, if there are mice in the house this time of year, there's a good chance the nest will have young in it. Typically a mouse will have five or six young. They will begin to forage for themselves after about three weeks. The next generation can begin breeding after only 8 to 10 weeks.

Nests are usually round balls loosely constructed of any fibrous material such as shredded paper or cloth, twigs or leaves, feathers or fur and even insulation. The mating pair usually remains together throughout gestation and rearing of the young. When the young are ready to go off on their own, everyone goes their separate ways. Nests are constructed in well-hidden areas of a home, usually within 30 feet of a food source. Nests can be found in odd and even dangerous places such as unused cabinet drawers and electric appliances like refrigerators and stoves. Obviously this is a potential fire hazard considering the nest building materials.

Control should start outside the house. Find possible entryways and seal them up. Check the foundation and siding for possible flaws or holes. Fill in around water pipes or wiring that enters the house. Basically, any opening larger than 1/4 inch should be filled. Filling materials include caulk, expanding foam or, if the hole is large, patch with hardware cloth.

Next, mouseproof the inside by eliminating any possible food sources. Remember, this includes non-food seed sources such as bird seed, stored vegetable seeds, dog or cat food and grass seed.

When there are only a few mice to control, I prefer using snap traps. I realize this approach is not for everyone because it involves seeing and handling the trap with a dead mouse. But it is easy to use, inexpensive and effective. Typical baits on traps include peanut butter, nuts or other fatty food. I have found most effective a small piece of pecan tied with string to the trigger. I think it is because the string allows the mouse to tug slightly on the trigger, ensuring the mouse is in the proper position when the trap is triggered. The trap must be placed in the path of activity for the mouse. They typically walk along walls behind cabinets and appliances. Check for signs of activity and set traps in active runs. Set the trap perpendicular to walls with the trigger closest to the wall. Don't leave much room between the trap and wall. Check the traps daily.

Another option is toxic baits. Most baits today are anticoagulants that, when ingested, cause internal bleeding which leads to death. It is important to be cautious when using baits to make sure pets or other wildlife aren't endangered. Baits should never be left out in the open. Bait stations or small boxes with the bait inside are recommended so only the mouse can get at it. Baits have been around for a long time and some mice populations have become resistant.

Baits may also fail because of the way mice feed. Because mice usually only eat small amounts of food when they first come across it, they may not eat enough to kill them. If they get slightly sick, they will never go back to that bait again. This is called bait shyness.

Another cause for concern is the possibility of another animal, like a bird or cat, eating the poisoned mouse which could pass the poison on to it. Some bait stations come with one-way doors so when the mouse enters it cannot exit. This would be best if unintentional poisonings are to be avoided.