Don't Let Mice Run Rampant Indoors


Don't Let Mice Run Rampant Indoors

Mice are a common household pest in Utah. The house mouse does not hibernate, and as temperatures drop in the fall and early winter, they migrate into homes seeking food, warmth, and shelter. People do an excellent job providing these basic needs to mice. Mice investigate house perimeters for warm air and food odors leaking out from any opening. Mice only need a hole about the size of a #2 pencil (1/2” high by 3/8” wide) to gain access to your home. They are unwanted visitors capable of spoiling food with fur, urine and feces, and transmitting disease. A few important steps can minimize mice in the home.

Step 1: Exclusion

Examples of trap placement strategies: 1) an overall trapping strategy for a corner and adjacent wall baseboards; 2) trap placement for a corner; 3) two traps placed 1 inch apart near the middle of walls to prevent mice from jumping over them; 4) alternative placement for sprinting mice.

Search the perimeter of your house and look for possible entry points. All holes should be sealed using appropriate materials: caulk, sealant, and/or Xcluder. Before choosing a material to repair cracks and crevices, consult the Purdue fact sheet on selecting caulks and sealants. Expandable foam, steel wool, and copper mesh are not recommended. Steel wool will rust and disintegrate over time, and copper mesh can be easily pulled out of place by mice. One effective product that is robust and unpalatable to rodents is called Xcluder (found online).

Thresholds and door sweeps are the primary area of weakness in your house’s security. Replace thresholds and/or door sweeps with high-quality options such as a thick, brush-style door sweep. During installation, check to see if the eraser side of a #2 pencil will fit through any gaps and fix if necessary. Installing door sweeps will also keep out other pests, in addition to reducing heating and cooling bills.

Step 2: Inspect

Mice need three things: food, shelter, and warmth. Focus inspections in places where food is stored, as well as under, behind, or in appliances that generate heat (anything with a motor and the stove/oven). Also look in areas that are secluded, dark, and shadowy, especially corners.

Look for fecal pellets, urine droplets (which will illuminate under a blacklight), build-up of brown grease (sebum) along frequently traveled routes, gnaw marks, and tiny hairs (seen with a hand lens) in feces or stuck to openings in walls where mice squeeze through. You can also look and listen for mice activity. Again, think food, shelter, heat, shadows, and corners.

Step 3: Sanitation and Food Storage

Sanitation is pest management. Eliminating food sources through proper food storage in mouse-proof containers will take its toll on mouse populations. Sanitation and food storage stress mice, causing them to have fewer offspring, and to travel farther to find food. Remember, mice want food. Don’t let them have it!

Step 4: Trapping

bait station
Tamper-resistant, lockable bait box with block-formulated rodenticide can be applied on metal posts. Yellow blocks are non-toxic and bioluminescent. Boxes come in various sizes; choose appropriate size for your situation & pest (mice vs. rats).

The most effective and humane traps are the standard snap-traps with an expanded trigger. Traps should be baited with 3 or 4 different types of bait. Peanut butter, bacon, grain, and even a piece of string or dental floss tied to the trigger are good choices. Pregnant females make many trips per night to collect nesting materials like string. If you can trap one pregnant female, you have effectively eliminated at least one, and maybe up to 7 or more mice at once.

Place traps in high-activity areas located during your inspection. These are places where mice travel and feed. Place 4 to 6 traps per mouse. Position traps against walls with the cocked trigger facing the wall. Corners are great places to place traps, but traps should also be placed every six feet along walls in high activity areas. Never place traps right in front of a mouse entrance hole. Traps can also be placed inside lockable, tamper-resistant boxes (into which mice can enter) to protect pets and children.

After 3 days of trapping, remove the traps for a few days and then put them out again for 3 days, slightly shifting the locations of particular baits. If you had bacon in one spot, put peanut butter there next time, and shift the trap left or right of the previous placement.

Step 5: Baiting

Anticoagulant baits should always be used inside a protective box. Placement of the bait box indoors is similar to that of traps: high-activity areas and corners. They can also be used outdoors on either side of the garage door or other doors where mice may enter. Use tamper-resistant, lockable bait boxes adhered to the ground or any permanent object and preferably use a block formulation of rodenticide. (The small green pellets that homeowners may have used in the past have been removed from residential use to protect children and pets.) The down side to using a rodenticide to kill mice is that they often die in inaccessible areas, and the odor may last several days.

Using a variety of proactive exclusion and management measures can eliminate mice populations in the home.

-Ryan Davis, Arthropod Diagnostician