Roof rats are also known as black rats, although they are usually dark brown or black-gray in color, with a white-gray or black underside. They are sleek and slender, with large ears and a scaly tail that can be longer than their head and body.
Approximately 13-18 inches in length including the tail. They are generally smaller than Norway rats.
Roof rats are omnivorous, but they prefer fruit, vegetables, and cereal products. The food habits of roof rats resemble those of tree squirrels, since they both like a wide variety of fruit and nuts. They also feed on a variety of ornamental and native plant materials. Roof rats usually require water daily, although its diet may provide an adequate amount if high in water content. As with other rodent species, they are prolific breeders.
Roof rats are nocturnal feeders. They see poorly, relying more on smell, taste, touch and hearing to find food. 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 for consumption. They may also hoard food to be eaten later. They have an excellent sense of balance, and 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.
Roof rats are more aerial than other rats in their habitat selection and often will live in trees. Landscaped residential or industrial areas provide good nesting sites, as does vegetation of riverbanks and streams. They will often move into sugarcane and citrus groves and have been found in palm trees.
Roof rats are agile climbers, utilizing their long tails for balance, and frequently enter buildings from the roof or utility lines, which they use to travel from area to area.
Medical and Economic Significance:
Roof rats pose both a health and safety hazard. It has been implicated in the transmission of a number of diseases to humans, including murine typhus, leptospirosis, salmonellosis, rat-bite fever, and plague. It is also capable of transmitting a number of diseases to domestic animals and is suspected in the transference of ectoparasites from one place to another.
In addition to consuming and contaminating stored food and animal feed, roof rats will gnaw on wiring (which can pose a fire hazard), and tear up insulation to use it for nesting material. They may also feed on the fruit and vegetable portions of commercial and residential trees and garden plants.
Roof rats are very sensitive to changes in their environment and have a strong tendency to avoid new objects in their environment, so baiting or trapping on the ground or floor may have little effect. They may take several days before they will approach a bait station or trap.
Proper sanitation is somewhat more effective in lessening Roof rat infestations. Secure garbage cans with heavy lids and avoid letting it accumulate. Store bulk foods, bird seed and dry pet food in tight-fitting containers, and remove standing water outside in pet food bowls, etc. Harvesting citrus and other fruit in a timely manner and picking up fallen fruit promptly will also help reduce Roof rat populations.
Seal any openings larger than 1/4 inch to exclude both rats and mice. Openings where utility pipes enter buildings should be sealed tightly with metal or concrete. Seal all vents and openings with concrete or heavy-duty metal screening. Equip floor drains and sewer pipes with tight-fitting grates with openings less than 1/4 inch in diameter. Doors, windows and screens should fit tightly; it may be necessary to cover edges with sheet metal to prevent gnawing.
Outside, mow, trim or remove ground cover plants that grow over one foot in height. Stack firewood, lumber, and other materials at least one foot away from walls and fences. Prune the tops of palm trees and remove dead fronds. Remove tree limbs that overhang roofs, and prune trees so that branches do not touch fences, overhead wires, or the branches of adjacent trees.
The Norway Rats are different than the Roof Rat. They have a thicker, heavier body, and a shorter tail. They have a more blunt snout. They are usually more brown in color than the Roof Rats. They prefer to live at ground level, hence their presence in the sewers. They seem to be highly dependent upon people for food and shelter sources. Like all rats, they have poor vision, and rely primarily upon their sense of smell and their highly specialized senses of feel and balance to survive.
Norway rats will eat nearly any type of food. When available, they favor fresh, wholesome items over stale or contaminated foods. They prefer cereal grains, meats and fish, nuts, and some types of fruit and will readily feed on household garbage. Rats require 1/2 to 1 ounce of water daily when feeding on dry foods but need less when moist foods are available. They use their keen sense of smell to locate food items and to recognize other rats. Norway rats are primarily nocturnal, though may become active when there is a large population, during bad weather or if their food source is threatened. They have poor eyesight and are colorblind, and depend on their excellent sense of smell, taste and touch, and especially their sense of sound, the frequency of which is greater than that of humans. They also use their sensitive body hairs and whiskers to navigate and prefer to move along walls. Their sense of taste is excellent and they can sense contaminants, which can lead to bait rejection. Female Norway rats are prolific breeders, and may come into heat every 4 or 5 days, and they may mate within a day after a litter is born. The average female rat has 4 to 6 litters per year, which can reach maturity as early as 8 weeks, and may successfully wean 20 or more offspring annually.
The Norway rat is found generally at lower elevations but may be found wherever humans live. They burrow to make nests under buildings and other structures, beneath concrete slabs, around ponds, in garbage dumps, and various other locations where food, water, and shelter are present.
Norway rats usually construct nests in burrows at or below ground level. Nests may be lined with shredded paper, cloth, or other fibrous material. Although they can climb, Norway rats tend to inhabit the lower floors of multi-story buildings. Their presence indoors can be detected by droppings, urine stains, or signs of fresh gnawing. Tracks can be seen in sand and on dusty surfaces.