Orange County Mosquito and Vector Control District
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Description

The roof rat (Rattus rattus) is agile and slender, with a tail longer than its head and body. Roof rats frequently enter buildings and move about neighborhoods by using utility lines and fences as runways. They prefer to feed on wild bird seed, pet food and many of the fruits and nuts (including those that people do not eat) commonly found in residential backyards.

Certain landscape plants are used as homes by roof rats and other flea-carrying animals. Many plants native to California are good choices for landscape use and do not encourage rats. For a list of suggested native plants, click here.

rats Rat educational material. Click on the thumbnail to download the PDF.

Disease

Rats and their fleas are capable of transmitting a variety of human diseases. Among the diseases transmitted by rats, bubonic plague is perhaps the best known and the most serious. County residents are fortunate because there have been no outbreaks of plague in Orange County in recent history. The potential of such outbreaks could increase if rat populations are allowed to increase unchecked.

Flea-borne typhus is another rat-borne disease that exists in certain areas of Orange County. This disease, like plague, can be transmitted by rat fleas.

Recognizing Roof Rat Activity

The homeowner should be aware of these signs of roof rat activity:

Partially eaten fruit and vegetables. Eaten Oranges
Snail shells under bushes, on fences, or near nesting sites.  
Signs of gnawing on plastic, wood, or rubber materials. Larvae
Rub marks caused by rats' oily fur coming in repeated contact with surfaces or objects. Pupae
Rat droppings are usually signs of significant rat activity. The droppings are randomly scattered on a runway, feeding location, or shelter. Droppings are dark in color, spindle shaped and about 1/2 inch long.

What We Do

When an Orange County Mosquito and Vector Control District Inspector comes out to a residence for a rodent service request, the Inspector will assess the situation to see what is the best way to handle the rodent problem. Every house and every situation is different and needs to be treated as such. Some measures that might work in your neighbor's yard will not necessarily work in your yard. 

When the Inspector comes to your house he/ she will tour around your house and yard to point out potential attractants to rodents as well as potential sites where they could be entering structures. Depending on the situation, removal of these attractants may be all a homeowner needs to do to take care of the rodent problem.


(click above for a larger interactive map)

IVM Products

Integrated vector management (IVM) is a decision-making process for the optimal use of resources in the management of vector populations. These decisions are made in order to reduce or interrupt transmission of vector-borne diseases, and prevent nuisance vector populations from impacting the quality of life.

The approach seeks to improve the efficacy, cost-effectiveness, ecological soundness and sustainability of vector control activities.

The key objectives of Integrated Vector Management include:

  • The selection of proven vector control methods based on knowledge of vector biology and ecology, and disease transmission.
  • Utilizing of a range of interventions, separately or in combination and often synergistically, integrating all available and effective measures, whether chemical, biological, or environmental.
  • Collaborating within the health sector and with other public and private sectors that impact vector control.
  • Engaging local communities and other stakeholders.
  • Knowledge and compliance with public health regulatory and legislative frameworks.

The District’s management policy for roof rat (Rattus rattus) control is to use the objectives of IVM in the following fields: education and source reduction.

To learn more about rat IVM practices please refer to the District's IVM Plan.

Education

The District has a multifaceted roof rat education program that includes:

  • Presentations and participation in local outreach events to educate the public about rodent control practices.
  • The creation and distribution of training DVDs for homeowners to educate them about rats, how to reduce rat populations, and how to rat-proof their residence.
  • Extensive literature on rat control, rat trapping, common entry points for rats on houses and mobile homes, vegetation that attracts rats, alternative ground cover that rats are not attracted to, how to rat-proof homes, and many other publications are available in print and electronically.
  • Inspectors educate homeowners and neighborhood groups about rats on their property and how to remove sources that would attract rats onto the property. 
  • Staff attends local and national educational conferences to learn about advances in rat control techniques, products, and other measures to better educate and protect the public from rats and the potential harm they can cause.

Source Reduction

Good environmental management practices are the most effective approaches to roof rat control. Sanitation and good housekeeping are the first steps in a successful rat control program. The homeowner can help control rat populations by doing the following:

  • Harvest all fruit, especially oranges, avocadoes, peaches, apricots, plums, walnuts and tangerines as soon as they ripen. 
  • Never leave pet food outside overnight.
  • Keep pet food in sealed metal containers if stored in the garage or other outbuildings.
  • Keep palm trees and yucca plants well trimmed.  Algerian ivy, oleander, bougainvillea, and other thickly matted plants should be periodically thinned and trimmed well away from roofs, walls, fences, utility poles, and trees. For a complete list of plants that rats nest in, click here.
  • Store wood and lumber piles on racks at least 18 inches above the ground and 12 inches away from walls. Storage boxes housed in utility sheds should be stacked close together and in an orderly fashion.  Clean up debris piles.
  • Repair leaky faucets and eliminate any other unnecessary standing water.

When renovating the yard and/or planning new landscaping, undesirable landscape vegetation should be eliminated from the plans and replaced by vegetation types that do not afford harborage to rats.  A list of alternative landscaping (e.g. ground covers) is available on this website.

What You Can Do

When it comes to rodent control around your own house, there are a number of things you can do to make your house "less attractive" to rats. Some actions are as simple as bringing in pet food at night, or harvesting fruit in your yard, to exclusion techniques you can use around the house.

Habitat Management

Roof rat survival and prosperity are dependent upon the existence of three basic environmental conditions:

  • Abundance of food
  • Available source of water
  • Access to suitable harborage

Good environmental management practices are the most effective approaches to roof rat control. Sanitation and good housekeeping are the first steps in a successful rat control program. The homeowner can help control rat populations by doing the following:

  • Harvest oranges, avocadoes, peaches, apricots, plums, walnuts and tangerines as soon as they ripen. Pick up all fallen fruit.
  • Never leave uneaten pet food outside overnight.
  • Keep pet food in sealed metal containers if stored in the garage or other outbuildings.
  • Keep palm trees and other plants well trimmed. Algerian ivy, creeping fig, oleander, bougainvillea, and other thickly matted plants should be periodically thinned and trimmed well away from roofs, walls, fences, utility poles, and trees. For a list of plants that rats often nest in, and plants that generally do not attract rats, consult our bulletin, California native plants for the home landscape..
Ivy Oleander
Bouganvillea

Store wood and lumber piles on racks at least 18 inches above the ground and 12 inches away from walls (click here to see video). Storage boxes housed in utility sheds should be stacked close together and in an orderly fashion. Clean up debris piles. Repair leaky faucets and eliminate any other unnecessary standing water.

When renovating the yard and/or planning new landscaping, undesirable landscape vegetation should be eliminated from the plans and replaced by vegetation types that do not afford harborage to rats. For lists of appropriate plants, consult our bulletin, California native plants for the home landscape.

Building Maintenance

Roof rats can enter a home through small exterior openings of less than one inch in diameter. For common roof rat entry locations, click here. Important steps a homeowner can take to exclude rats are inspecting and repairing:

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

All access openings should be screened with 1/4 inch galvanized hardware cloth and inspected at least once a year for the condition of the repair. Gaps around pipes and electrical conduit should be sealed, and cracks around doors and windows should be weatherproofed. (To see a video of a rat entry being sealed, click here). Tree limbs should be kept well away from the eaves, roof, and exterior walls of the house.

Vent Opening Blocked with Steel Wool Opening screen with Galvanized Hardware Cloth
Opening screen with Galvanized Hardware Cloth

Rodent Proofing Your Residence

Rodents in the walls and attic of your home are unnerving. Your house, garage, and sheds are favorite nesting places for rodents. These unwanted guests will set up housekeeping, rear their young, chew on electrical wires, feed on pet food, and anything else within reach.

Another reason to discourage rodents from sharing your residence is the possible chance of disease, not to mention the panic some people experience upon discovery of rodents indoors.

*** Make sure you do not put out any baits or poisons if rodents are in your structure. Rats can die inside the walls or in your attic and can cause an odor problem and a fly problem. ***

Rodent proofing is an easy "Do-It-Yourself" project. The average home can be rodent proofed in one to two hours by a homeowner with average skills using common tools. All supplies needed are inexpensive and available through your local home improvement center.

Suggested Tools Needed:
  • Hammer
  • Staple gun
  • Pliers
  • Screwdriver
  • Putty knife
  • Ladder
  • Tin snips
  • Portable drill
  • Measuring tape
Materials Needed:
  • ¼" Hardware cloth (sold by the yard)
  • House vent insert
  • Crawl space vent
  • Stucco or plaster patch
  • Bronze or steel wool
  • Door threshold
  • Door weather stripping
  • Flashing (sheet metal)
  • Wood snap traps
  • Metal trash can (for pet food)
  • Sheet metal screws
  • Expanding foam filler w/steel wool

Click here to view problems and solutions for examples of how to exclude rodents from your structure.

Trapping

Rat traps may be use in the yard and inside buildings with good results. Wood snap traps are inexpensive, give positive results, and eliminate the possibility of a poisoned rat dying in an inaccessible area. Rat carcasses within a structure can cause serious odor and fly problems.

Several traps may be set at once for maximum effectiveness.

For best results, try several different baits to see which is accepted most frequently by rodents. If fresh food is abundant for the rodents, use a bait somewhat different than what is available to them.

These baits should be kept in fresh condition for best results and should be securely fastened to the trigger.

Traps should be placed along known rat runways such as fence tops and walls, where rat activity is evident. Securely anchor traps to an immovable object to keep any trapped animals at the placement site.

  • Adjusting Snap Traps

    Before baiting the trap, check for sensitivity of the trigger. The trap should be sensitive enough to snap closed when the rodent feeds or otherwise touches the baited trigger, but not so sensitive as to snap if roaches or other insects come in contact with it. Trigger sensitivity can be checked by lightly touching the trigger of a set trap with a screwdriver. If the trap does not snap, the metal trigger tab can be bent outward to make it more sensitive. If the trap is too sensitive, the trigger tap can be bent inward.
  • Setting a Snap Trap

    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 the bar to the trigger tab. Carefully place the trap as recommended in the diagrams. Better results are usually obtained if two traps are set side-by-side.
  • Prebaiting Traps

    It is also a good idea to prebait, which is to use a baited but unset trap, so that the rodent can become familiar with and start feeding on the baited trap. This requires only two or three days, after which the traps can be set.

    The following baits are most attractive to rats:
    • Bait Options
      • Peanut butter on steel wool
      • Dried meats
      • Anything else the rodent would have to tug to remove from the trap

  • Maintaining Traps

    The working parts of the trap should be oiled occasionally using mineral oil, never petroleum based oils. Petroleum oils may act as a repellent to rodents. Never store traps near insecticides or other chemicals, or handle domestic animals or pets before setting out traps. These can also cause traps to take on a repellent odor.

Proper Disposal of a Rat Carcass

Using a plastic bag, place your hand in the bag like a glove, pick up the carcass with the bag, invert the bag or turn bag inside out, tie a knot at the end of the bag, and dispose of rat in a trash container with a secure lid.

 

Vector Reduction Manual For the District's specific guidelines on how to avoid or reduce mosquitoes, rats, red imported fire ants, and flies please refer to recommendations in the Vector Reduction Manual: Procedures and Guidelines.
 Orange County Mosquito and Vector Control District