Color: Brown with black mixed in, to gray, to black on top with white; gray or black underside.
Size: Roof rat (black rat, ship rat) adult head-plus-body length is 6-8 inches; tail length is 7-10 inches.
Roof rats are very agile climbers and usually live and nest above ground in shrubs, dead fronds of palm trees, upper portions of buildings, trees, and dense vegetation such as ivy.
They are most often found in enclosed or elevated spaces in attics, walls, false ceilings, and cabinets.
Roof rats usually begin searching for food shortly after sunset. If the food is in an exposed area and too large to be eaten quickly, yet not too large to be moved, they will usually carry it to a hiding place before eating it. Many rats will cache or hoard considerable amounts of solid food, which they may or may not eat later. When necessary, roof rats will travel considerable distances for food. They can often be seen at night running along overhead utility lines. They may live in trees or attics and climb down to a food source. This is important from the standpoint of control, for traditional baiting or trapping on the ground or floor may intercept very few roof rats. Roof rats have a strong tendency to avoid new objects in their environment and this can influence control efforts. These rats may take several days before they will approach a bait station or trap.
Rats see poorly, relying more on smell, taste, touch and hearing. They are considered to be colorblind, responding only to the degree of lightness and darkness of colors. Roof rats also have an excellent sense of balance. They use their tails for balance while traveling along overhead utility lines and are very agile climbers.
The food habits of roof rats resemble those of tree squirrels, since they both like a wide variety of ornamentals, vegetables, fruits, and nuts. Snails are a favorite food, but don’t expect roof rats to eliminate a garden snail problem. In some situations, pet food and poorly managed garbage may represent a major food resource. Roof rats usually require water daily, though their local diet may provide an adequate amount if high in water content.
Rats inhabit the dwellings of humans, commercial buildings, industrial yards, and farming operations.
- Their urine odor can be inhibiting to the operations of these structures.
- Their scats and grease rubs can become an eyesore and odiferous.
- They chew and gnaw through construction materials to make dens.
- They tunnel through insulation and plastic membranes of commercial roofs.
- They burrow under concrete slabs causing settling of buildings and fractures of foundations.
- They chew through electrical wires, causing shorts and fires.
- To obtain water, rats will chew through water pipes and hoses. Rats spend 2% of their day chewing and gnawing on natural and man-made materials.
Public Health Damage:
Rat bites are common, especially in areas with high rodent infestations in close proximity to humans. Infants and the elderly are the most vulnerable to foraging rats. Rats are also a reservoir for many zoonotic diseases such as; bubonic plague, septicemic plague, pneumonic plague, sylvatic plague, murine typhus, scrub typhus, rickettsialpox, leptospirosis, rat bite fever, trichinosis, salmonellosis, hantavirus, lymphocytic choriomeningitis and rabies.
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. Sanitation programs must always include both the outside and inside of affected buildings.
- Outside all rubbish piles must be eliminated.
- Improper handling of garbage and re use (e.g. improper selection, use and maintenance of industrial dumpsters) may result in a prime source of food and shelter for rodents and thus, attract them to any building.
- When it is necessary to accumulate food refuse, it must be kept in rodent-proof containers until it is removed from the premise. Industrial dumpsters, for example-especially those used around food-serving establishments-must be carefully selected for proper proper volume, pick up schedule, cleaning, placement, and other factors so as to not attract rodents to the property.
- Grass, weeds, and other undesirable vegetation adjacent to building should be removed. If the building is landscaped, it should be properly maintained. Over grown landscape planting can provide rodents with both cover and food.
- Lumber, rock piles, rubbish, old equipment, construction materials etc.., should all be eliminated if possible. Items that must be kept should be stored atleast 18 inches (46 cm) off the ground and 12 inches (31 cm) away from walls or fences.
- Indoor, al potential rodent harborages must be identified and eliminated or modified. Such areas as obscure corners, shelves, under and in cabinets, worktable, lockers and equipments must not be overlooked or neglected as these dark, out-of-the way areas provide rodents with ideal harborage.
- Where possible, rodent proofing of these areas as well as stairwells, machinery, double walls, false ceiling and floors, hollow tile partitions and boxed in pipes and conduits may be necessary.
- In warehouses and storage areas of commercial facilities, products should be on pallets (preferably 8 to 12 inches (20 to 31 cm) off the floor), 18 to 24 inches (46 to 61 cm) from adjacent walls, not stacked more than one to two pallets wide and separated by an aisle.
- Homeowners should do proper reuse management, storage practice and the proper feeding of pets and wildlife to attracting rodents to the yard or home.
- Residential garbage cans must not be overfilled and contain tight-fitting covers.
- Woodpiles and any other type of outdoor storage should be elevated off the ground to help eliminate potential rat or mouse harborage.
- Backyard infestation of rats are commonly associated with exterior doghouses, bird and squirrel feeders, improper garbage management, improper composting practice and vegetable gardens and fruit trees that are not properly maintained.
[B] Rodent Proofing (Exclusion):
Ideally, the best way to control mice and rats is to make it impossible for them to gain entry into structures. It can be difficult or impractical to exclude mice completely as even adult mice can pass through opening 3/8-inch 91.0 cm) wide. Furthermore, mice commonly enter building through open doors or windows or are carried into buildings inside merchandise. Nevertheless, it is good pest management for building owners to rodent proof a building as much as possible.
When considering rodent proofing, every possible route of rodent access to the building must be considered. Generally, all opening greater than 1/4 –inch (0.6 cm) should be sealed to exclude mice. For rats, all openings greater than ½-inch (1.3 cm) should be sealed.
- Points where utility lines penetrate a wall are likely access sites for rodents. The opening around service conduits such as water, electricity, air conditioning, drain pipes, and vents should all be sealed. Sheet metal, hardware cloth and mortar can be used to seal the spaces around these and other types of openings. Copper mesh stuffing and coarse steel wool can be stuffed into gaps and holes, but should be sealed with mortar or the appropriate durable sealant to provide for a long term closing of the holes.
- Broken basement windows, warped doors and unscreened vents are all invasion routes for mice and rats. Vents should be covered with a metal grill-work, backed by rust-resistant screening.
- The spaces beneath doors should be checked and, if need be, reduced. A 12-inch (30 cm) sheet metal (26 gauges) kicking plate should be attached to the outside of the door with the lower edge not more than ¼ inches (6 mm) from the floor. The door casing should also be protected with sheet metal to prevent mice and rats from widening cracks by gnawing.
- Rodent can be deterred from climbing pipes on the outside of buildings by fitting metal guards around the pipes. These should be made of 26-gauge sheet metal, fitted close to the wall at the rear and projecting 12 inches (35 cm) outward form the pipe. An added measure to deter climbing by Norway rats and mice is to apply a 12-inch band of hard glossy paint around the outside of brick or stone walls about 3-1/2 feet above the ground. A 12-inch band of glossy paint around a vertical pipe will also help prevent climbing. These measures however, may not be very effective against roof rats.
- Roof should be checked to see that shingles are down tight and sheathing is complete. Also check roof ventilators, screen vent and louvered wall vents. Use hardware cloth (1/4-inch width screening) to prevent larger animals from entering through vents. Screen chimneys and vent pipes if they are serving as entryways.
Additional Rodent proofing Tips :
- 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.
[C] Population Control:
When food, water, and shelter are available, rat populations can reproduce and grow quickly. While the most permanent form of control is to limit food, water, shelter, and access to buildings, direct population control is often necessary.