Effective Control of Rats and Mice

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Introduction

Do you hear scampering and scratching sounds in the walls of your home at night?

Is there evidence of gnawing or chewing on your property? Are food packages damaged? You may have an infestation of mice or rats.

Other telltale signs include:

• droppings and urine
• burrows or holes in and around foundation walls
• tracks on dusty surfaces

Mice and rats are prolific breeders. You must tackle the problem of occasional invaders immediately, or you will eventually have a severe infestation.

Identification of Rats and Mice

In urban areas, you are likely hosting the house mouse (Mus musculus). It has large ears and is light brown to dark grey, with a lighter colour on its belly.

The deer mouse (Peromysus maniculatus) may invade buildings near fields and woodlands at the onset of cold weather. It is brown or grey in colour, with a white belly and feet. The white colour on the underside of the tail is perhaps the easiest way to distinguish between a deer mouse and a house mouse.

The Norway rat (Rattus norvegicus) has coarse, brown-ish fur, small ears, a blunt nose and a stocky body that may weigh up to 0.5 kilograms (1 pound). The tail is shorter than its overall body length. It builds elaborate systems of tunnels and burrows at ground level. It prefers damp areas such as crawl spaces or building perimeters.

The roof rat (Rattus rattus) is more slender than the Norway rat. It is usually black with a pointed muzzle and large ears. Its tail is longer than its overall body length. An agile climber, it prefers to live in trees, vines and other dense vegetation. It will infest attics, rafters or roofs, and the upper stories of buildings.

Health Concerns

Mice and rats are carriers of disease. Some diseases are spread by contact with the urine and droppings. Breathing dust raised during the cleanup of droppings can cause illness, therefore it is important to practice safe cleanup procedures.

Safe Cleanup

• Never sweep or vacuum dry droppings.
• Dampen droppings and debris with a bleach and water solution before wiping up.
• Rubber gloves and a dust mask should be worn during cleanup.
• Wash hands and exposed clothing thoroughly after cleanup.
• Wear gloves to dispose of dead rodents.
• Wrap dead rodents in a plastic bag and put in the garbage, or hazardous disposal site.

Rodent-Proofing Your Home

The first line of defense is to eliminate easy entry points. Mice can squeeze through cracks as small as a dime, while rats can enter through a quarter-sized hole. Even the small gaps created by worn thresholds under doors will allow mice access to your home.

• Use metal weatherstripping under doors; weatherstrip windows.
• Patch cracks in foundations.
• Stuff steel wool around pipes etc. before caulking or plastering.
• Cover dryer vents, attic vents or soffits with fine mesh metal screening.

Make Your Home Less Appealing

• Remove cosy nesting sites in unused clutter around the house and garage.
• Cut tall grass and weeds back from the house.
• Secure garbage in containers with tightly fitting lids.
• Raise woodpiles about 30 centimetres (1 foot). Place them a distance from the house.
• Never place fatty or oily food waste, eggs or milk products in the composter.
• Use a layer of heavy metal mesh between the soil and the bottom of the composter.
• Eliminate water sources such as leaky taps, sweating pipes and open drains. Rats need, and are attracted by, water sources.
• Cleanliness in the kitchen is essential; dry goods, including grains and dry pet foods, should be stored in metal or glass containers.

Physical Control of Rats and Mice

Traps

Metal snap traps are easy to use and very effective if well positioned and set properly. Live traps have trapdoors that are triggered when rats or mice walk over them. Follow these guidelines for both types:

• Set the traps at right angles to the wall, with the baited end of the trap closest to the wall.
• Set a large number of traps, i.e. 1 trap per metre (yard) along walls, or 5 to 10 traps per visible mouse hole.
• Allow a warm-up period of 3 to 4 days (bait the traps but do not set them) so that the rodents become comfortable taking the bait.
• Try using baits of strong-smelling, sticky foods (like peanut butter or bacon grease) mixed with oats, raisins or gumdrops.
• Reuse the traps - they are more attractive to the rodents.
• Move traps to different locations if the bait does not start to disappear regularly.
• Reset the traps in 2 to 3 weeks to catch maturing young rodents.

Glue traps, sticky boxes or tube traps catch both large and small rodents and may be an effective choice if snap traps fail, or for use in hard-to-reach places. They can be used with or without bait.

If you decide to use live traps or glue traps because they appear to be more humane, consider what you will do with the trapped animal:

• If you intend to release the rodents, check the traps daily. Mice quickly die of stress and exposure if they are held without food and water.
• Mice caught in glue traps do not die immediately; use an oil (e.g. mineral oil) and apply pressure with a small stick to 'unglue' live animals. Wear heavy gloves. Or, live trapped rodents may be disposed of by drowning them in a bucket of soapy water.
• Note that snap traps generally kill the rodents instantly.

Ultrasonic devices emit sound waves or vibrations that rodents dislike. The devices may drive rodents out of certain areas and into areas where baits or traps have been set. This may help increase the effectiveness of control methods. Rodents may adapt to the devices over time and return to areas within the device range.

Chemical Control of Rats and Mice

Poisoned baits are a common method of rodent control. The bait must be used in areas out of the reach of children, pets or non-target animals.

• Never scatter poison bait over the ground or inside a building.
• Bait stations (e.g. those used by professional pest control operators) must be tamper-resistant.
• Read and follow all label directions and precautions.

Use of baits or poisons cannot replace the need to rodent-proof homes or properties.

Anticoagulant rodenticides inhibit the clotting of blood. These products are sold as liquids or powders to mix with seed, paraffin blocks, bait packages or loose pre-mixed bait. Domestic class products may contain the following active ingredients: warfarin, diphacinone, chlorophacinone or bromadiolone.

Note: anticoagulants are usually highly toxic. See Precautions re: accidental poisonings.

Non-anticoagulant poisons may include ergocalciferol or cholecalciferol in domestic class products.

Repellents containing thiram can be used to discourage mice from damaging young trees and other ornamentals.