Facts, Identification & Control
There are numerous species of rats found within the United States, but this article will focus upon those rats that most frequently create pest issues in homes and businesses. These rats are the Norway rat (Rattus norvegicus) and the Roof rat (Rattus rattus). In addition, two other rats, the Rice Rat Oryzomys palustris) and the Cotton Rat (Sigmodon hispidus) will not be elaborated on in this article, but are mentioned since they are identified by the Centers for Disease Control and Prevention as hosts of hantavirus and therefore noteworthy from a public health perspective.
Norway Rats are frequently called brown or sewer rats. They are large, bulked-up looking rats that can grow to lengths of about 13-16 inches when measured from their nose to the tip of their tail. Coloration is primarily gray on their underside and reddish or grayish-brown to black on the top of their body. The ears and tail of the Norway rat are hairless and the tail is shorter than the length of the rat’s body. With blunt snouts, Norway rat adults weigh about 7-18 ounces.
Roof Rats are commonly called black rats and are smaller than Norway rats. Adults range in weight from about 5-10 ounces. Their tails are longer than the rest of their body and are uniformly dark colored. The underside of the roof rat’s body is grayish to white. The muzzle of the roof rat is pointed and the overall appearance of the roof rat is much more streamlined and sleek looking than a Norway rat.
Behavior, Diet & Habitat
Roof rats are adept climbers and not surprisingly are apt to build their nests in locations above ground. However, they may sometimes also build nests in burrows. These rats are primarily active at night. Scientists have noted that the roof rat’s long tail is adapted to enhance their ability to climb and functions to assists them in balancing. Both roof rats and Norway rats have a well-developed sense of smell and are wary of new things that are introduced into their home range. Roof rats are not accomplished swimmers and are not usually found in sewers.
Norway rats are usually active at dusk or during the night and are inactive during daylight hours. However, when a Norway rat population grows so large that competition from other rats for food, water and harborage increases, some members of the rat community may seek to find new areas to colonize during the daytime. Norway rats build their nests in underground burrows where they mate, rear their young, store food and seek refuge from predators. Norway rats can climb, but not as well as roof rats, and are strong swimmers.
Roof rats are omnivores and will feed on many types of vegetation such as fruits, grains, seeds and grocery produce. Also, roof rats are likely to consume insects. Just like Norway rats, roof rats destroy far more foodstuffs by contamination from feces and urine than from consumption.
Norway rats are also omnivores and will eat just about anything that is found near where humans discard food. Also, Norway rats may prey upon fish, poultry, mice, birds, small reptiles and amphibians. . They may eat vegetation, but prefer to meat or meat-related wastes.
As mentioned above, roof rats prefer aboveground nesting locations in shrubs, trees, and dense vegetation. Roof rats entering homes are generally found in raised or secure enclosures such as walls, cabinets, attics, and false ceilings. Roof rats are likely to found in coastal, near-coastal areas and port cities.
The preferred habitat of Norway rats is just about anywhere people reside. Some of their habitats include garbage dumps, sewers and fields. In most of our urban areas, Norway rats may be seen scurrying around after dark looking for food in garbage cans and other places where human refuse is found. Their burrowing habitats include soil along building foundations, under woodpiles and other piles of debris. Should Norway rats infest a structure, they most likely will live in the basement or ground floor.
Roof rats are polygamous and group themselves into colonies of multiple males and females. Mating may occur year round in locations where the environmental conditions are sufficient. Adult females are able to reproduce at 3-5 months old, can produce up to five litters each year with about 5-8 young in each litter. Adult roof rats usually live about one year.
Norway rats are also polygamous and form colonies of many males and females. Mating generally peaks in the warmer months of the year, but may occur year round in some areas. Female adults will produce about seven litters per year and will mate again about 18 hours after giving birth to her litter of about eight pups. The reproductive potential of one female Norway rat is about 50-60 young per year.
Signs Of An Infestation
- Observation Rats are not usually seen during the day unless disturbed from their protective harborage or because of intolerable competition from other rats. If rats are seen during the day that usually means a very large rodent population is nearby.
- Burrows Or Nests Holes in the ground around foundations, plus nests in attics or trees are evidence of a rat problem.
- Sounds Noises produced by scurrying rats, scratching in the walls or other noises from nest building may tip off the property owner to a rat problem.
- Gnaw Marks Rat need to chew and gnaw on wood, plastic and other hard surfaces in order to keep their teeth chiseled down.
- Rub Marks As rats move from one location to another, they stay close to vertical surfaces in their environment that they use to assist in their nightly navigation. Therefore, the body oils on a rat’s fur gets deposited on corners and edges of walls and around holes and gaps they use to enter into a wall void.
- Droppings Rats produce a lot of feces and the presence of their fecal droppings is a surefire way to spot an infestation. When droppings are seen, it is a good practice to remove those droppings and later inspect to see whether new droppings were deposited. ALWAYS USE RESPIRATORY PROTECTION WHEN REMOVING RODENT DROPPINGS.
How Orkin Treats For Rats
Norway rats and the roof rats are very different in their habits, habitats and behavior, so the first requirement of a rat treatment program is to correctly identify the rat and develop a treatment plan that works for that species. Another important treatment component is customer education so the customer understands the concepts of the proposed control program.
Orkin pest management professionals (PMPs) practice all techniques involved in Integrated Pest Management for rodents. Rat treatment involves both non-chemical and chemical methods. Some of the more important non-chemical methods are:
- Exclusion and sealing of sites greater than ½ inch (about the size of a dime) using screens, flashing, door sweeps and other materials to keep rats from entering a structure.
- Interior and exterior sanitation to minimize available food and water that supports a rat population.
- Keeping vegetation thinned out or removed from the perimeter of buildings.
- Removing clutter and any debris that creates hiding places rats can use as harborage sites.
- Using traps and other mechanical means to remove rats.
Rat control using chemical products involves baits designed to kill rats. Care must be exercised to ensure that baits are properly placed and the use instructions on the product’s label are strictly followed. One of the more common techniques for bait use is to place the bait formulation in a tamper proof rodent bait station that protects the bait from accidental exposure to non-target animals or people. In situations where rats are not controlled with conventional products, fumigation of transport vehicles or rat ground burrows may sometimes be needed.