Rodent Control
To control rats, implement the following procedures:
Rodentproofing - Rodentproofing is changing the structure of buildings in order to prevent entry of rats and mice. In considering rodentproofing, you must know that
- Rats can squeeze through cracks ½ inch wide; mice, ¼ inch wide. Any place a pencil can be poked, a mouse can go.
- Rats can climb the inside of vertical pipes 1½ - 4 inches in diameter.
- Rats can climb the outside of vertical pipes up to 3 inches in diameter and any size if within 3 inches of a wall.
- Rats can jump vertically 36 inches, horizontally 48 inches, and reach horizontally or vertically 15 inches.
- Rats can jump 8 feet from a tree to a house if the branch is 15 feet above the roof.
- Rodentproofing requires the use of rodent-resistant materi¬als. The following materials are considered rodent resistant:
- Sheet metal (26 gauge or heavier).
- Perforated metal (24 gauge or heavier with openings no more than ¼ inch).
- Hardware cloth (19 gauge or heavier with openings no more than ¼ inch).
- Brick with mortared joints.
- Cement mortar (1:3 mixture).
- Concrete (1:2:4 mixture).
A gnawing edge is the edge of substances which rats can gnaw through. The gnawing edges must be protected with rodent-resistant materials. Places to rodentproof are edges of doors, windows, holes where pipes enter buildings, ventilation holes in foundations, roof vents, exhaust fans, and eave vents. Rodents can also enter homes through toilets. To be effective, rodentproofing must block all possible rodent entry points. During the first 2 weeks of complet¬ing rodentproofing, searching rodents will find breaks in the rodentproofing. Inspect frequently during this time and promptly repair any breaks. It will also be necessary to eliminate the rodents trapped indoors due to rodentproofing.
Sanitation - Good housekeeping or sanitation is a basic factor in rodent control. Eliminating food, water, and harborage for rats and mice can reduce rodent populations rapidly. To implement sanitation practices:
- Clean up garbage and rubbish.
- Properly store garbage (Metal garbage cans should have tight fitting lids).
- Properly store food (store raw or prepared foods and refuse indoors in covered, rat proof containers or in rat proof rooms).
- Store pet food and bird seed in rat proof containers.
- Remove harborages (remove piles of rubbish, trash, junk, boxes, and protected enclosures).
- Dry up sources of water.
- Pick fruits and vegetables when ripe so rodents will not feed on them.
Sanitation must be used constantly in rodent control to be effective. Yearly clean-up programs are generally ineffective for rodent control.
Predators - Many people have relied on cats and dogs to control rats, but in general cats and dogs are not good tools for control. Food put out for pets is excellent rat food. Most people put out more food than the pet can consume in one day. Rats then clean the bowl overnight. Because pets are well-fed, they are too lazy to hunt. Studies have shown that although predators can keep an area rat free, they can not remove an existing infestation.
Birds of prey, hawks and owls, feed on large numbers of rodents. Barn owls are exceptional rat killers and a pair can be expected to kill several hundred rats over a one year period.
Many species of non-poisonous snakes are very beneficial in rodent control. Snakes such as rat snakes, king snakes, pine snakes, black racers, and coach whips eat numerous rodents and are important in controlling rodent popula¬tions. Do not kill non-poisonous snakes.
Trapping - Trapping is an underrated method of control¬ling rodents. One reason trapping is often overlooked is that snap traps have been around for a long time and are cheap. Traps can be used to eliminate rats where poison baits would be dangerous, to avoid dead rat odors, and to eliminate bait-shy rats.
It is important to place traps where the rats are. Rats and mice are used to human odors so there is no need to use gloves when handling traps. Since mice travel only 10-30 feet but rats travel 100-150 feet from harborages, more traps are needed to trap mice than rats in a house.
Rats and mice also have different behavior around new objects. Rats are cautious, and it may be a week before they approach a trap. Mice are curious and will normally approach traps the first night. If you don’t catch a mouse in the first few nights, the trap is in the wrong location. To help rats overcome trap shyness, place traps unset, in place, for several days. This allows rats to overcome shyness and results in better catches.
Baited traps rely on the rat’s being attracted for feeding. The bait must compete with other available foods, so no one bait is ever the best bait for all locations. Rodents living on garbage or spoiled food prefer something fresh. The follow¬ing are some baits that have proven to be successful:
- Whole nuts for rats and mice.
- Raisins or grapes for roof rats.
- Sardines packed in oil for Norway rats.
- Peanuts or peanut butter for rats and mice (soak whole peanuts in water overnight; old peanut butter becomes rancid so replace it frequently).
- Dry rolled oatmeal is excellent for mice.
- Bacon squares.
- Small wads of cotton for mice and rats (they look for nest material).
- for mice.
Baited traps should be set a right angles to rat runs . Traps can be nailed to rafters and beams to take advan¬tage of areas where rats travel. Set traps along walls, behind furniture, and near holes. Remember to set traps where children and pets will not be hurt.
Runway traps - catch rats when they accidentally bump the trigger. Runway traps are available or can be made from snap traps by enlarging the trigger with cardboard, hard¬ware cloth, or screening . There is no bait to go stale, so there is an increased chance of success. In placing runway traps, the trap should be placed at right angles tothe wall or along runways. To hold the trap in place on pipes or rafters, use rubber bands, nails, or hose clamps.
Glue boards - Special glue can be placed in pie tins or paper plates. The glues do not harden but will hold a rat in place. Other rats become curious and also get caught. Placing a small piece of bait in the center of a glue board can increase effectiveness. Dusty and wet conditions will impair the trap’s effectiveness. Glue boards are better suited for mice and safe for children and pets. Boards may be cleaned with cooking oil.
Poison Baits - Traps are effective usually when dealing with small numbers of rats or mice. When rats are plentiful or where unsanitary conditions exist with harborage, poisoned baits are an effective tool to use with trapping.
Poison baits are available as ready to use, premixed baits. They come in many forms; parafinized blocks for outdoor use and high humidity areas, treated meal, seeds, or parafinized pellets in bulk or in “place packs” for indoor use. Water baits are sold as packets of concentrate that are mixed with water. They are administered with a chick fount, available at most feed stores, and are useful in areas where rodent food is abundant but water is in short supply.
There are three types of rodenticides; acute toxins, calcium releasers and anticoagulants. Most acute toxins are no longer available due to the risk of accidental poisoning. Zinc phosphide baits react with stomach acids to produce phos¬phine gas. This product is restricted use and mostly used for agricultural rodent control, because it offers little risk of secondary poisoning of beneficial predators. It has no anti-dote and is not appropriate for use around children, pets, or livestock. One new acute toxin that is considered safe and effective is bromethalin. Bromethalin is a mitochondrial poison that shuts down the rodent body’s ability to produce energy. It also has no antidote, and is considered a minor threat of secondary poisoning because it causes the rodent to stop feeding days before it dies, so most of the poisonhas been excreted prior to death and possible ingestion by a predator or pet. Vitamin D3 or cholecalciferol is a calcium releaser that causes too much calcium to be released into the blood, resulting in kidney, liver, or heart failure. The advantages of vitamin D3 are that it kills anticoagulant-resistant rodents and there is no problem of secondary poisoning of pests or wildlife that eat poisoned rodents. The most common rodenticides are the anticoagulants. The older, multidose anticoagulants include chlorophacinone, coumafuryl, diphacinone, pivalyn, valone, and warfarin. The newer generation of anticoagulants are effective after a single dose and include brodifacoum, bromadiolone, and difethalone. The single-dose anticoagulants are generally effective against rodents resistant to the older multidose compounds. Rodents poisoned with anticoagulants die from bleeding internally. Because the effects show up days after taking the bait, they do not associate their poisoning with the bait. Anti-coagulants are considered safer roden¬ticides than the acute poisons, because larger doses are necessary to poison humans or pets and these poisons have a simple antidote, Vitamin K1.
Whenever a rodenticide is used, safety must be the first consideration. Poison baits must be placed where they are inaccessible to children, pets, livestock, and wildlife. Where rodent runs are exposed and in all outdoor situations, tamper proof bait boxes must be used. A tamper-proof bait box or station must be inaccessible to a 4 year old child or a dog. This means that the station can not be opened and the bait can not shaken out. Bait blocks must be secured inside the station or if loose bait pellets or meal is used, then the station must be secured to the ground so a child, dog or raccoon could not move it. Baits stations should always be placed near where rats live and breed or along travel routes.
About 1 pound of anticoagulant bait should control most rats in and around homes. The baits should be placed in sta¬tions with 1/4 pound of bait per station. Shallow containers for holding the bait are best. For added effect, water may be provided separately for the rats to drink. Pick up dead rats wherever they are noticed. A few cases of pet poisoning have been reported when pets feed on dead rats or mice. When rats die in areas where they can not be removed, it may be necessary to ventilate the area or use odor absorbent or masking products. Usually anticoagulant poisoned mice are dehydrated and do not produce severe odor after death. Rats on the other hand are large enough to produce an unpleasant odor for up to two-four weeks if they die in inaccessible locations.
When you control your rats, encourage your neighbor to control their rats at the same time. The greater the area that is controlled, the more effective the results will be and the longer it will take new rats to migrate back to your property.
Check with your local county health department to determine whether a rodent control project is active in your neighborhood. They may be able to offer advice and aid in controlling rats. Remember it is no disgrace to acquire some rats, but it is a dangerous to maintain them.
