The first strategy to avoid problems is to keep rodents out of your space.
Seal out rats and mice by covering openings larger than one-fourth of an inch with rodent-resistant materials such as 1/4-inch hardware cloth (wire mesh), concrete, sheet metal, brick or mortar. Regularly check for cracks or openings around the foundation, attic, vents, and places where pipes or cables enter the building. Add a sheet-metal collar around pipes to seal off the space between the pipe and the wall. Keep the space under doors less than a quarter of an inch. Cover the edges of doors with metal to prevent gnawing.
You also can discourage rodents by removing food sources and nesting and hiding places. Rodents need food, water, and nesting sites to thrive and reproduce. Killing rats and mice without also reducing food and nesting sources does not work for long. Rats do not like to travel far, typically nesting, traveling and feeding within a 250-foot radius. Focus efforts within 250 feet of your area of concern.
Keep food – including pet food and birdseed – in rodent-proof containers. Either do not feed pets outdoors or remove food dishes promptly after feeding. Clean up spilled birdseed or stop feeding the birds. Birds toss what they do not like, so feeding seed that birds prefer cuts down on spilled seed. Keep garbage cans covered tightly and empty them regularly. Line compost bins with quarter-inch hardware cloth.
Keep firewood, ivy, brush, and other materials away from buildings to reduce hiding places for burrows. Cover fiberglass insulation in areas accessible to rodents. From a mouse or rat’s perspective, insulation is a perfect nesting area.
Remember that rats can climb and burrow. Keep shrubs 2 or 3 feet away from walls and roofs. Tree branches should be 6 feet from roofs, eaves, attic vents, and utility wires. Add a strip of heavy, rough gravel 2 feet wide and 6 inches deep next to building foundations and walls.
Trap mice or rats with snap-traps instead of poisoning them. Rodent poisons are slow-acting, so the poisoned rats often crawl into the wall and die, leaving a smelly, difficult cleanup problem. Traps are effective. Place traps along walls or rafters where rodents regularly travel. Place several traps in a row with the triggers toward the wall, or two traps with their long ends against the wall and triggers each outward from one another. This makes it more likely to catch the mouse or rat even if they jump. Check and empty traps daily and add fresh bait as needed. If there is no activity after three or four days, move the traps. Wear gloves when you dispose of trapped rodents; double bag their remains and place them in the trash.
Finally, work with neighbors and other community members. While mice can be a single-household problem, rats are a problem for the entire neighborhood or community. It may take a community effort to reduce food and nesting sites for rats.
For more information, go to the state Department of Health website, www.doh.wa.gov/ehp/ts/Zoo/rodent.
Dr. Diana T. Yu is the Health Officer for Thurston and Mason counties. Reach her at 360-867-2501 or email@example.com.