San Mateo County Environmental Health, San Mateo, CA. 94403 (650) 372-6200
General Information Rats and mice have been associated with people for hundreds of years. They live on our food and waste products and inhabit our buildings. Rodents can cause serious damage to structures, equipment, furniture, and utilities. In addition to causing damage to our surroundings, rodents have the potential to spread a wide variety of diseases, including leptospirosis, trichinosis, hantavirus, rickettsial diseases, rabies, and bacterial food poisoning to name a few. Rodent control must be achieved to lessen structural damage and decrease disease potential. This is effectively accomplished by proper yard maintenance and comprehensive rodent proofing. Complete rodent control begins with a thorough inspection. Look around your property, and focus on places where rats may hide. Some of the more typical hiding places are illustrated in this pamphlet. Walk around the outside of your house during the day, checking each of these potential problem areas carefully. During the inspection, look for the following signs: droppings tracks gnawing damage burrows runways grease marks urine stains live or dead rodents rodent sounds rodent odors (especially mice) Ideally, the best way to control mice and rats is to make it impossible for them to find any way to get into structures. It is good pest management (for both rodents and insects) for building owners to rodent proof the building as much as possible RODENT SURVIVAL DEPENDS UPON THE EXISTENCE OF THREE BASIC ENVIRONMENTAL FACTORS: FOOD, WATER and HARBORAGE.
ROOF RAT Rattus rattus Has a tail which is longer than the body. The total length may reach 12-16 inches. Is most active at night. Eats fruit, berries, snails, pet food and nuts, especially walnuts, etc. Lives in ivy and other dense vegetation, also in attics, garages and woodpiles. Climbs trees, walks utility lines and fences. Roof Rat evidence includes chewing noises, rat droppings, chewed walnut and snail shells and rub marks on inside walls. Droppings evident in attic and garage. NORWAY RAT Rattus norvegicus Generally lives underground in elaborate burrow systems. Also lives in basements, sewers, and creekbanks. Water must be readily available. Has a tail which is shorter than the body. Eats garbage, pet food and many other foods. HOUSE MOUSE Mus musculus Tail is 3-4 inches (7-10 cm) long. Body is small and slender, 2 to 3 _ inches (7-10cm) long. Average weight is 5/8 to 1 ounce. Lives within the house. Attracted to any accessible food such as pet food. Basic Rodent Proofing Measures
Substandard repairs and remodeling can alter a structure s rodent proofing. The vast majority of rodent proofing breakdowns is the result of damage after initial construction. Repairs for rodent proofing are usually very simple and cost very little. Periodic inspection of your property should be conducted to insure that proper rodent proofing is still intact. The following list illustrates the types of rodent proofing breakdown in homes in the order of how frequently they occur. 1. Subfloor space ventilation openings must be intact. A C B D A. the screen is pushed out or detached B. loose flat cut in the wire mesh C. the hole for pipe or wire is too large D. hand or fingers can be pushed up between screen and foundation 2. Subfloor crawl space entry opening must be sealed with a door or a lid that will exclude finger-size objects. Removable lids should fit so that the lid must be lifted up to open. Be sure to check under the door.
3. At the junction of roof pitches the overhanging roof may form a triangular recess which allows rat entry at the very back. Most of these areas are inaccessible. The best permanent seal is a piece of 1/4 inch mesh, galvanized screen. A piece larger than the opening should be jammed tightly in place with a stick. Heavy arrows indicate typical locations of recess holes. Vents that open into the attic should be screened. 4. Poorly fitting side or main garage doors should be weatherstripped at the bottom if your fingers can fit underneath the door. 5. Old wooden stairs on houses without concrete foundations may have holes, which need to be sealed with the 1/4 inch, galvanized screen. 6. Some unusual holes may exist, such as roof mounted chimney covers that have no pipes in them and open directly into the attic. Trapping
Trapping rodents is a perfectly acceptable method of control. It should be done in combination with or after rodent proofing is completed. Trapping is especially desirable when poisons cannot be used near food, small children, or where domestic animals or livestock are present. Traps should be used indoors to prevent the serious odor problems that can occur when poisoned rodents die in inaccessible areas. DO NOT USE RAT POISON INSIDE THE HOUSE. Types of traps: Rodent snap traps are available in two sizes. The smaller trap is designed for mice and the larger is designed for rats. It is very important to choose the proper size trap. Several rat traps should be set to maximize trapping effectiveness. Bait selection is important for trapping success. Peanut butter, nutmeats, bacon, pieces of apple, and moistened oatmeal are effective baits. Try to find one that is the most acceptable to the rodents. Bait the trap but do not set it until feeding has occurred on the trap. Once they feed on the trap, set with fresh bait. Placement: Correct placement of snap traps is crucial to their effectiveness. Place traps in areas frequented by rats. Look for common signs such as rodent droppings, urine stains, dark smears or rub marks. Rats establish runways along fence tops and next to walls. Poisoned Baits: Poisoned baits are NOT recommended for use inside the home. Rodents may die in inaccessible places and cause odors. Poisoned baits may be useful in the yard to kill rodents AFTER an effort is made to reduce their normal food supply and BEFORE harborage is removed. Roof Rat Control Through Yard Management
One way to control roof rats is to eliminate their nesting places. Roof rats are much too mobile to be easily controlled by restricting their food sources. Poison baits are useful only when used along with good yard management. By paying close attention to how the yard is maintained, ROOF RATS CAN BE KEPT UNDER CONTROL! Firewood, building materials and other such things that are stored in yards for extended periods must be stacked as neatly as possible to prevent nesting places. They must not be allowed to become overgrown by plants. They should be stored at least eighteen inches off the ground and away from the sides of buildings and away from fences. The following illustration shows proper storage. The heavy arrows indicate spacing from the fence. 12 18 Look closely at the next two illustrations. They represent before and after landscaping conditions. Unpruned landscaping is the primary cause of roof rat infestations in suburban yards. BEFORE Plant Species which harbor roof rats and should be avoided are: algerian ivy blackberry bamboo pampas grass AFTER Some important roof rat food sources that can be controlled are: snails nuts fruits pet foods wild bird seed How Norway Rats Enter the Home
Main sewer line. Sewer rat entering basement through burrow. Sewer rats can burrow 8 feet or more through solid ground. Breaks in sewer lateral. Invasive tree roots damaging sewer line. Norway (sewer) rats have the ability to enter the home through the sewer lines. They find breaks in drain pipes caused by faulty joints, poor construction or by tree roots, and then burrow through the ground, dumping the excavated earth back into the sewers. Thus they come up into yards, under sidewalks, driveways, flower beds and enter a building. To achieve long term rodent control is to eliminate their food and shelter sources as well as sealing all points of entry. The removal of both harborage and food will have far greater impact than the short term success achieved by occasional baiting or trapping. The San Mateo County Vector Control Unit advises on appropriate baiting/trapping procedures. Please call for additional information on the control and prevention of rodent problems. Should the homeowner wish to seek the services of a licensed pest control operator, the yellow pages of the phone directory may be consulted under the heading Pest Control. The following checklist has been developed to help you identify signs and factors contributing to a rodent infestation.
Rodent evidence: live rodents sounds tracks burrows odors gnawing urine stains dead rodents runways rub marks nests rodent hairs droppings Exterior building inspection: burrows gaps under doors damaged vent screens pipes roof jacks chimney damage cracked foundations conduits leading into the structure openings around ducts or vents gaps under garage door foundation crawl space broken or missing shingles other Outdoor factors: bird feeders overhanging tree limbs wood piles poorly maintained landscaping garbage cans open or broken sewers/ditches pet food breaks in sidewalks water source (bird baths, ponds, leaky faucets, etc.) fruit trees