The house mouse is the most successful rodent in adapting to life with people. It's found almost everywhere people are, feeding on human food, sheltering in human structures and reproducing at a rapid rate. The house mouse is the most troublesome and economically important vertebrate pest, contaminating millions of dollars worth of food, damaging property and causing electrical fires with its constant gnawing. Mice may enter a building from the outside and spread through a structure along pipes, cables and ducts. Although large numbers can build up in food service areas or trash rooms, one or a few mice can survive practically anywhere.
Many control failures against house mice are due to a lack of understanding of mouse biology and habits. A pair of mice can produce 50 offspring in one year. Because they seek food over a range of only 10 to 30 feet, traps, glue boards and bait must be placed close to the nest to be effective. Remember that good inspections are critical for successful mouse control.
Sounds - Sounds are common at night where large numbers of mice are present; listen for squeaks, scrambling and sounds of gnawing.
Droppings - A house mouse produces many droppings per day; mouse droppings are frequently the first evidence that mice are present. However, be aware that large cockroaches and bats may produce droppings similar to house mice. Look along runways, by food near shelters and in other places mice may frequent.
Urine - House mice occasionally make small mounds known as "urinating pillars." These consist of a combination of grease, urine and dirt and may become quite conspicuous. Look for many small drops of urine using a blacklight. Urine stains will fluoresce under ultraviolet light. (Mouse urine spots are not as easy to detect as those made by rats.)
Grease marks - Like rats, mice produce greasy smears where dirt and oil from their fur mark pipes and beams.
Runways - Most mouse runways are indistinct trails free of dust and are not readily detectable.
Tracks - Look for footprints or tail marks on dusty surfaces or on mud; use a nontoxic tracking dust (like talc) to help locate mice within buildings.
Gnawing damage - Newly-gnawed areas on wood are light in color, turning darker with age. Look for small tooth marks and enlarged cracks beneath doors. Mice make wood chips with a consistency like coarse sawdust around baseboards, doors, basement windows and frames and kitchen cabinets.
Visual sightings - Mice are often active in daylight and this may not indicate a high population (as it does with rats). Use a powerful flashlight or spotlight at night to confirm mouse presence.
Nest Sites - Inspect garages, attics, basements, closets and other storage places for evidence of nests. Be alert to fine shredded paper or similar materials; these are common nest-building materials.
Mouse Odors - Mice produce a characteristic musky odor.
The number of mice observed or food consumed is not reliable as a census technique with mice. Unlike rats (which may travel widely within a building leaving tracks on many patches of dust) mice do not range widely.
Control and prevention of mice is a three-part process, which includes sanitation, mouse-proofing and population reduction with traps or baits. Sanitation and mouse-proofing will help prevent mice from entering buildings. When a mouse population already exists, some kind of lethal control is necessary. Otherwise, mice, which reproduce rapidly and can find food almost anywhere, will continue to be a problem.
Sanitation - Good sanitation makes it easier to detect signs of mouse infestation. It also increases the effectiveness of baits and traps by reducing available food. However, the best sanitation will not eliminate mice; they require very little space and small amounts of food to survive and reproduce.
Mouse-Proofing - Completely mouse-proofing a building is difficult because mice are reported to be able to squeeze through an opening as little as 1/4 inch high. To mouse-proof a building:
Snap Traps If used correctly, snap traps are very effective in controlling mice. They must be set in the right places, in high numbers and in the right position or mice will miss them entirely. Always place traps in areas that are inaccessible to students. Here are some tips to keep in mind when trapping mice:
Multiple-catch mouse traps catch up to 15 mice without being reset. Some brands are called "windup" traps; the windup mechanism kicks mice into the trap. Others use a treadle door. Live mice must be humanely killed.
Mice are curious and like to investigate new things. They enter the small entrance hole in the trap without hesitation. Odor plays a role too; traps that smell "mousy" catch more mice. Place a small dab of peanut butter inside the tunnel entrance to improve the catch.
Glue boards can be effective when other methods have failed against a "bait-shy" mouse or when food is abundant. As with other traps, placement is the key. Locations that are good for other types of traps are good sites for glue boards.
"Building out" mice and trapping are the most effective control methods. Rodent baits should be used only in emergency situations to supplement these methods. If there is a repeated need to use baits, it is likely that sanitation and mouse-proofing should be improved. Remember that rodent baits are poisons. Additionally, use of baits in schools represents special problems because of incidents where students have moved or tampered with rodent baits. In schools, baits should be used only after nonchemical control measures have been instituted.
Children, pets, wildlife and domestic animals must be protected by putting the bait in tamper-resistant bait boxes in inaccessible locations. Using baits alone will not provide long-term control of mice.
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