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Rats are some of the most troublesome and damaging rodents in the United States. They consume and contaminate food, damage structures and property, and transmit parasites and diseases to other animals and humans. Rats live and thrive under a wide variety of climates and conditions; they are often found in and around homes and other buildings, farms, gardens, and open fields. People do not often see rats, but signs of their presence are easy to detect. In Arizona, the most troublesome rats are two introduced species: the roof rat and the Norway rat.

It is important to know which species of rat is present in order to place traps or baits in the most effective locations.


Norway rats, sometimes called brown or sewer rats, are stocky burrowing rodents that are larger than roof rats. Their burrows are found along building foundations, beneath rubbish or woodpiles, and in moist areas in and around gardens and fields. Nests may be lined with shredded paper, cloth, or other fibrous material.


Roof rats, sometimes called black rats, are slightly smaller than Norway rats. Unlike Norway rats, their tails are longer than their heads and bodies combined. Roof rats are very agile climbers and usually live and nest above ground in shrubs, trees, and dense vegetation such as ivy. In buildings, they are most often found in enclosed or elevated spaces in attics, walls, false ceilings, and cabinets.


In areas where the roof rat occurs, the Norway rat may also be present. While rats are much larger than the common house mouse, a young rat is occasionally confused with a mouse. In general, very young rats have large feet and large heads in proportion to their bodies, whereas those of adult mice are much smaller in proportion to their body size. While both rats and mice gnaw on wood, rats leave much larger tooth marks than those of a mouse.


Because rats are active throughout the year, periodically check for signs of their presence. Once rats have invaded your garden or landscaping, unless your house is truly rodent proof, it is only a matter of time before you find evidence of them indoors. Experience has shown it is less time consuming to control rodents before their numbers get too high, and fewer traps and less bait will be required if control is started early. Inspect your yard and home thoroughly. If the answer to any of the following questions is yes, you may have a rat problem.

  • Do you find rat droppings around dog or cat dishes or pet food storage containers?

  • Do you hear noises coming from the attic just after dusk?

  • Have you found remnants of rat nests when dismantling your firewood stack?

  • Does your dog or cat bring home dead rat carcasses?

  • Is there evidence rodents are feeding on fruit/nuts that are in or falling from the trees in your yard?

  • Do you see burrows among plants or damaged vegetables when working in the garden?

  • Do you see rats traveling along utility lines or on the tops of fences at dusk or soon after?

  • Have you found rat nests behind boxes or in drawers in the garage?

  • Are there smudge marks caused by the rats rubbing their fur against beams, rafters, pipes, and walls?

  • Do you see burrows beneath your compost pile or beneath the garbage can?

  • Are there rat or mouse droppings in your recycle bins?

  • Have you ever had to remove a drowned rat from your swimming pool or hot tub?

  • Do you see evidence of something digging under your garden tool shed or doghouse?


Three elements are necessary for a successful rat management program: sanitation measures, building construction and rodent proofing, and, if necessary, population control. Sanitation is fundamental to rat control and must be continuous. If sanitation measures are not properly maintained, the benefits of other measures will be lost, and rats will quickly return.


Good housekeeping in and around buildings will reduce available shelter and food sources for Norway and, to some extent, roof rats. Neat, off-the-ground storage of pipes, lumber, firewood, crates, boxes, gardening equipment, and other household goods will help reduce the suitability of the area for rats and will also make their detection easier.  Garbage, trash, and garden debris should be collected frequently, and all garbage receptacles should have tight-fitting covers. Where dogs are kept and fed outdoors, rats may become a problem if there is a ready supply of dog food. Feed your pet only the amount of food it will eat at a feeding, and store pet food in rodent-proof containers.


For roof rats in particular, thinning dense vegetation will make the habitat less desirable. Climbing hedges such as Algerian or English ivy, star jasmine, and honeysuckle on fences or buildings are very conducive to roof rat infestations and should be thinned or removed if possible, as should overhanging tree limbs within 3 feet of the roof  to make it more difficult for rats to move between them.


The most successful and long lasting form of rat control in buildings is to "build them out." Seal cracks and openings in building foundations, and any openings for water pipes, electric wires, sewer pipes, drain spouts, and vents. No hole larger than 1/4 inch should be left unsealed to exclude both rats and house mice. Make sure doors, windows, and screens fit tightly. Their edges can be covered with sheet metal if gnawing is a problem. Coarse steel wool, wire screen, and lightweight sheet metal are excellent materials for plugging gaps and holes. Plastic sheeting, wood, caulking, and other less sturdy materials are likely to be gnawed away. Because rats (and house mice) are excellent climbers, openings above ground level must also be plugged. Rodent proofing against roof rats usually requires more time to find entry points than for Norway rats because of their greater climbing ability. Roof rats often enter buildings at the roof line area so be sure that all access points in the roof are sealed. If roof rats are travelling on overhead utility wires, contact a pest control professional or the utility company for information and assistance with measures that can be taken to prevent this.

  • Repair or replace damaged ventilation screen around the foundation and under eaves.

  • Provide a tight fitting cover for the crawl space.

  • Seal all openings around pipes, cables, and wires that enter through walls or the foundation.

  • Be sure all windows that can be opened are screened and that the screens are in good condition.

  • Cover all chimneys with a spark arrester.

  • Make sure internal screens on roof and attic air vents are in good repair.

  • Cover rooftop plumbing vent pipes in excess of 2 inches in diameter with screens over their tops.

  • Make sure all exterior doors are tight fitting and weatherproofed at the bottom.

  • Seal gaps beneath garage doors with a gasket or weather-stripping.

  • Install self-closing exits or screening to clothes dryer vents to the outside.

  • Remember that pet doors into the house or garage provide an easy entrance for rodents.

  • Keep side doors to the garage closed, especially at night.

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