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Environmental Health Division
Environmental Health Division

Control & Preventions of Rodents



General Information 

Public Health Importance 

Signs of Rodent Activity 

Common Rodent Entry Location 

Steps to Rodent Control 


Rodents & Vegetation 


Chemical Control (Rat Baits)

Guidelines When Speaking to a Pest Control Service

Safety Precaution for Clean-up



Commensal (domestic) rodents live in close association with humans. These commensal rodents are nocturnal and tend to move indoors to warmer areas during late fall or early winter and return to the outdoors in late spring or early summer, or remain indoors if food and suitable harborage are available. Commensal rodents generally have poor sense of vision, but they have acute sense of smell, touch, and taste. They tend to gnaw through any material that is softer than their enamel, and they are generally good climbers, jumpers, swimmers and burrowers. There are three species of domestic rodents:


Roof Rat

(Rattus rattus)

Alias: Black Rat/Tree Rat

Roof rat is slender and agile, and Its tail is longer than the head and body lengths combined. Its total length may reach 12 to 17 ¾ inches and can weigh up to about ¾ of a pound. Roof rat nests above ground and lives in ivy, wild blackberry vines, attics, garages, and wood piles. It will enter buildings if given the opportunity, and often use utility lines and fences as runways. It prefers to feed on fruits, nuts, ivy, and pet food commonly found in residential areas.

Norway Rat

(Rattus norvegicus)

Alias: Sewer Rat/Wharf Rat

Norway rat is larger and more aggressive than the roof rat. It has smaller eyes and ears than the roof rat, and its tail is shorter than the combined head and body length. Its total length may reach 18 inches and may weighs up to about 1 lb. Norway rat lives and nests in underground burrow system and is generally found in agricultural areas, creeks, sewers and occasionally developed neighborhoods. It can also live in buildings, basement, creekbanks, waterfronts, under blackberry vines, under wood piles. It feeds on garbage, pet food, meat scraps, cereal grains, fruits and vegetables.

House Mouse

(Mus musculus)

House mouse is small, slender bodied, and the tail is longer than the length of its head and body. Its body size ranges from   2-1/2 to 3-4/5 inches long. Its body color is generally grayish brown with a gray or buff belly. House mice is agile climbers and can fit through openings as small as ¼ inches in diameter. It eats many types of food, but prefers seeds and grain. It normally travels an area averaging 10 to 30 ft. in diameters.

Size & Shape of Rodent Droppings:

Roof Rats and Norway Rats may establish nests in:  

Roof Rats prefer to feed on:

 Rodent Dropping
  • Algerian ivy
  • Other heavy shrubbery
  • Wood and lumber piles
  • Storage boxes
  • Utility sheds
  • Rubbish piles






  • Avocados
  • Natal plums
  • Oranges & other ripe fruits
  • Pet food left out at night
  • Walnuts
  • Snails
  • Bird and grass seed






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Rodents can be very destructive pests that can contaminate foods and preparation areas, cause costly structural damage, and even cause house fires by chewing on electrical wires. Most importantly, rodents are reservoirs and vectors for numerous diseases.

Selected Infectious Disease Associated with Rodents 




Caused by a bite of a rat flea infected with pathogenic bacterium Yersinia pestis. While there have not been any reports of plague in Berkeley, the potential for an outbreak may increase as the rat population expands.


Bacterial “food poisoning” that may be transmitted when rodents defecate or urinate on food, dishes, kitchen counters, floors, and other objects associated with humans thus contaminating food or drink.


Caused by the bacterial spirochete, Leptospira spp., which humans may become infected through contact with water or ingestion of food contaminated with urine of infected rats.

Murine Typhus

Also known as flea-borne typhus is caused by Rickettsia typhi and it can be transmitted to rodents or other hosts such as humans when infected fecal material from a flea is scratched into the skin or rubbed into the flea bite or an open sore or wound.

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  • Damaged, partially eaten fruits and nuts, such as walnuts, oranges, and avocados.
  • Broken snail shells under bushes, on fences or near nesting sites.
  • Signs of gnawing on plastic wood or rubber materials.
  • Greasy rub marks caused by the rat’s oily fur coming in repeated contact with painted surfaces or wooden beams.
  • Rodent droppings are usually signs of significant rodent activity. The droppings are randomly scattered and will normally be found close to a rat runway, feeding location, or near shelter. Droppings can be found in forced air heaters, swimming pool heater covers, and water heater closets.
  • Sounds (gnawing, etc.) from attic, subfloor areas and wall spaces.
  • Visual Sightings on utility cables, tops of fences, or in trees.
  • Burrows in the ground, and adjacent to sewer lines are signs of Norway rat. activity.

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  • Broken or missing foundation vent screens or attic vent screens.
  • Overlapping roof.
  • Open wooden meter boxes (in older homes).
  • Space between roof jack and vent pipe.
  • Under or on sides of garage door.
  • Brick chimneys which have settled away from house.
  • Crawl hole with poorly fitted lid.
  • Tile roof.
  • Broken or open building sewers which connect to the main sanitary sewer. (Norway rats).
  • Toilets. (Norway rats).

Common Rodent Entry and Harborage Locations 

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Roof rat survival depends upon the existence of 3 basic environmental factors: (1) Food, (2) Water, and (3) Harborage.

STEP 1: Eliminate Food and Water

  • Remove all potential sources of food from the premises, such as bird seed left out for birds. Routinely harvest ripe fruit and pick up all fruit that has fallen to the ground.
  • Store pet food in metal containers with tight sealing lids and do not leave uneaten pet food outdoors.
  • Avoid storing food in garages and storage sheds unless it is in rat-proof covered metal containers.
  • Control snails and clean up pet feces because they are favored food items.
  • Keep trash cans closed at all time with tightly fitted lids.
  • Repair leaking eliminate any other faucets, sprinklers, or other piping. Keep drain covers tightly fastened and  unnecessary standing water.

STEP 2: Destroy Rats

  • Rats should be snap trapped if they are inside a residence or building. Place traps near nesting areas or where rats are likely to hide. Do not place traps where children or pets will disturb or be harmed by them. Remember, snap traps are very DANGEROUS!
  • Poisoning with baits indoors is NOT recommended because a rat may die inside the structure and create an odor and fly problem. Poison baits may be used when following recommended guidelines.
  • Remove dead rats by placing animals in tightly sealed containers for proper disposal.
    Clean and disinfect the affected areas.

STEP 3: Eliminate Shelter & Harborage

  • Close all openings larger than ¼ inch to exclude rats and mice.
  • Repair or replace damaged vent screens.
  • Remove all trash and debris.|
  • Stack woodpiles, lumber and household items at least 18 inches above the ground, and 12 inches away from fences and walls.
  • Trim trees, bushes and vines at least 4 feet away from the roof.
  • Remove heavy vegetation away from buildings and fences.                                                 
  • Thin vegetation to allow daylight in and remove rat hiding places.

STEP 4: Maintain a Rat Free Property

  • After rats have been reduced, prevent reinfestation by keeping harborage and food sources to a minimum.

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Building Maintenance

Roof rats can enter even small exterior opening of a home. Important steps a homeowner can take are inspecting and repairing:

  • Basement windows and ventilation ports.
  • Attic vents and louvers.
  • Gaps between roof and chimney.
  • Tile roofs along the eaves
  • Vent pipes and shafts.

All openings such as these should be screened with ¼ inch galvanized hardware cloth and inspected at least twice a year. Gaps around pipes and electrical conduit should be sealed and cracks around doors and windows should be sealed, and cracks around doors and windows should be weatherproofed. Tree limbs should be kept well away from the roof and walls of the house.

Rodentproof Your Building to Prevent Rodent Entry

  • Close all openings larger than ¼ inch to exclude rats and mice.
  • Repair or replace damaged vent screens.
  • Screen vents, holes and overlapping roof with 16 or 20 gauge ¼ inch hardware cloth.
  • Use sheet metal collars around pipe entrance on wooden walls.
  • Use cement fill around pipe in brick, stone or stucco walls.
  • Subfloor crawlspace entry hole must be sealed with a door or a lid that will excel finger size objects.
  • Removable lids should fit so that the lids must be lifted up to open.
  • Use sheet metal edging along door bottoms to prevent entry and gnawing by rats.
  • Repair broken or open building sewers to prevent sewer rats infesting property from broken or open sewers which connect to the main sanitary sewer where they may live.

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Many plants species harbor roof rats. Whenever possible, these plants should be replaced with species which achieve the desirable effects of ground cover, but will not contribute to the rat population. Characteristics to look for in a desirable ground cover are:

  • Plants should be low growing, not more than 10 inches in height.
  • They should not be climbers.
  • Fruiting plants should not be used.
  • Plants should provide soil stabilization.
  • Plants should require a minimum amount of water once established.
  • Once established, plants should be properly maintained.


  • Algerian ivy (Hedera canariensis)
  • Arborvitae (Thuja orientalis)
  • Bamboo (Bambusa spp.)
  • Date palm trees (Phoenix dactylifera)
  • Himalayan blackberries (Rubus procerus)
  • Italian cypress (Cupressus sempervirens)


  • African daisy (Arctotis)
  • Blue fescue (Festuca ovina ‘Glauca’)
  • Brown bean sedum (Sedum rubrotinctum)
  • Carpet bugle (Ajuga reptans ‘Bronze beauty’)
  • Chamomile (Anthemis nobilis)
  • Creeping fig (Ficus repens)
  • Creeping speedwell (Veronica repens)
  • Creeping thyme (Thymus sephyllum)
  • Dichondra (Dichondra repens)
  • Dwarf coyote bush (Baccharis pilularis)
  • Gazani
  • Germander (Teucrium)
  • Giant ajuga (Ajuga crispa)
  • Gold moss sedum (Sedum acre)
  • Hahns ivy (Hedera helix)
  • Japanese spurge (Pachysandara teminalis)
  • Mesembryanthemum floribunda
  • Mondo grass (Ophiopogon japonicum)
  • Nana (Juniperus procumbens)
  • Needle point ivy (Hedera helix)
  • Red spike ice plant (Cylindrophyllum speciosa)
  • Sand strawberry (Fragaria chiloensis)
  • Shore juniper (Juniperus conferta)
  • Snow-in-summer (Cerastium tomentosum)
  • Speedwell (Veronica repens)
  • Spring cinquefoil (Potentilila verna)
  • Trailing African daisy (Osteospermum fruticosus)
  • Vinca mior bodesi
  • Winter creeper (Euonumus fortunei)
  • Wooly yarrow (Achillea tomentosa)


 Why Compost?

Composting is nature’s way of recycling. It is a satisfying way to turn your fruit vegetable, and yard trimmings into a dark, crumbly, sweet smelling soil conditioner. Make sure you use a rodent proof bin and maintain compost so as not to become an attractant for flies and rodents.

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Trapping rodents is a perfectly acceptable method of control. Trapping is especially desirable when poison 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.

Types of Traps

Rodent “snap traps” are inexpensive and are available in 2 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.

What is the Best Kind of Bait?

Bait selection is important for trapping success. For best results,  try several different baits to see which is most acceptable by rodents. If fresh food is abundant for the rodents, use a bait somewhat different than what is available to them.



Roof Rats

Peanut butter, peanut butter mixed with raw oatmeal, fresh fruit, marshmallows, jellied candies, nut meats (walnuts, almonds, etc.).

Norway Rats

Bacon, meat scraps, fish (sardines).


Peanut butter, bread, raisins, bacon, strawberry jam.


Placement of snap traps is crucial to their effectiveness. Place traps in areas frequented by rats. Rats establish runways along fence tops and next to walls. Look for the presence of rat droppings when placing snap traps. Place the narrow end of trap containing the trigger against a wall or known runway. Snap traps can also be attached to pipes or studs with wire, nails or screws.

How to Set Snap Traps

To set a snap trap, apply recommended bait to the trigger. Pull back the bail with your thumbs. Hold the bail in place with one thumb while attaching bar to the trigger tab. Carefully place the trap as recommended above. Better results are usually obtained if 2 traps are set side by side. It is also a good idea to pre-bait, that is; use a baited but unset trap so that the rodent can become familiar with the baited trap. This requires only 2 or 3 days after which the traps can be set.

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Most rodenticides presently available for rat control are chronic anticoagulant formulas, which require several consecutive feedings to reach lethal levels or newer acute anticoagulants, which are usually lethal after a single feeding. All placed rodenticides must be checked often and replenished immediately when the supply is low. When the job is finished, uneaten rodenticides should be removed and disposed of according to the label.

Homeowners may purchase rodenticides at nurseries, feed stores, and hardware stores. All rodenticides should be handled carefully. Always follow all label precautions and recommendations.

A Berkeley Vector Control Technician can advise homeowners on appropriate baiting and/or trapping procedures, and will provide other 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.

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  1. The pest control operator should make a thorough inspection of your premises and provide a written report or diagram in which he/she:
    - Locates or describes entrances and rat proofing needs.
    - Lists harborage and food sources present.
    - Locates or describes entrances and rat proofing needs.
    - Lists harborage and food sources present.

  2. He/she should give attention to rodent proofing needs by:
    - Bidding and contracting for needed work or
    - Providing specifications and requirements for do it yourself or other means of repair.
    - Coordinating rodent exclusion with control measures.

  3. The pest control operator should:
    - Stress trapping or other capture techniques for indoor infestations (rats may die in walls or other inaccessible places and  cause bad odors when poison bait is used).
    - He/she should not make false claims for rodenticides, i.e., “this poison makes the rats dry up and they won’t smell” or “will cause the rats to go outside in search of water,” etc.

  4. Tropical rat mites may become bothersome when rodents are removed or controlled. Rat parasite control, if needed should be undertaken before or concurrently with rodent control.

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When handling rodents, these precautions should be followed to avoid the possibility of disease transmission.

  • Ventilate the affected area the night before clean-up by opening doors and windows.
  • Use rubber gloves.
  • Apply household disinfectants at maximum recommended concentrations to dead rodents, rodent droppings, nest and surrounding area, and allow for at least 15 minutes contact time before removal.
  • Clean the affected area with paper towels or a mop. DO NOT SWEEP OR VACUUM. Double bag the disinfectant-soaked rodent and clean-up materials securely in plastic bags and seal.
  • Before removing gloves, wash in disinfectant, then soap and water. Thoroughly wash hands with soap and water and dispose of gloves and clean-up materials with other household waste.

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ALWAYS KEEP IN MIND that trapping and chemical control alone will NOT achieve long term, permanent rat control. If the rats can be controlled and conditions that allow them to reproduce are removed, then we have achieved a longer lasting control. After the harborage has been removed, your property should be maintained harborage free so that the rats will not find the property attractive for reinfestation. Most people are capable of controlling rat problems if given the proper direction. The City is asking you to remove any conditions on your property that allow rat harborage. The continued maintenance and removal of harborage is recommended after the rats are controlled. At the same time, we are inspecting the neighborhood to find other properties with rat harbor-age.
The owner of property on which rodents or rodent harborage is found is responsible for the abatement and control of the problems.

For advice and more information on rodent prevention and control, contact the City of Berkeley Vector Control Program.

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