The Roof Rat, also known as the Black Rat or Ship Rat, is smaller than its cousin the Norway Rat, and is more commonly found in coastal and port cities. They not only damage materials by gnawing, they also eat and contaminate stored food, making them an important health concern as well.
The Roof Rat is thought to be of Central Asian origin, but they are now found worldwide. Adult Roof Rats are typically around 6” long, not counting the tail, which will always be longer than the length of the body. They can weigh between 5oz-9oz, but have been found to grow up to 12oz. Their fur is soft, smooth and ranges in color from brown with black mixed in to mostly black, with their underside white, gray or sometimes black.
The Roof Rat has a pointed muzzle, larger eyes and ears, and their tail is dark and scaly. Their droppings can be up to 1/2” long, spindle-shaped with pointed tips.
Roof Rats can begin breeding as early as 2 months and each pregnancy lasts about three weeks. The young are born blind and naked, and are weaned at about 3-4 weeks. Roof Rats have an average of 8 young per litter, and will have between 4-6 litters per year. The average Roof Rat will live between 9-12 months.
Roof Rats have very poor vision and are color blind, but their senses of hearing, smell, touch and taste are keenly developed. They are good runners, excellent climbers and jumpers, and if forced they are good swimmers.
A single Roof Rat needs between 1/2oz-1oz of food and 1oz of water each day, with the water often coming from its food. With access to a good food source, each Rat can produce over 100 droppings and up to 1/2oz of urine every day. Historically, bubonic plague has been associated with the Roof Rat and its fleas, which move from infected Rats to bite humans. Fortunately, plague has not been found in Rats in the United States for many years, though Rats can carry many other types of infectious bacteria, such as Jaundice and Salmonellosis, spreading these diseases through their droppings and urine.
Roof Rats are primarily nocturnal and are very cautious. They will constantly explore their surroundings, but they shy away from any new objects or changes. Roof Rats prefer to nest in upper parts of buildings, such as attics, and often nest outdoors in trees. Though Roof Rats are not as social as Norway Rats, there will often be several nests within a given location.
Roof Rats will eat practically anything, though they prefer fruit, vegetables and grains. When they find an acceptable food material they tend to eat their fill at one sitting and return time after time. Once established indoors, they tend to follow the same route between their nest and food source. Commonly used pathways will show dark rub marks where their oily fur makes contact. Roof Rats will gnaw through wood, walls and even hard plastic to get to food.
The key to Rat control is exclusion, or “Rat-proofing” the home. This is often the most difficult portion because adult Roof Rats need an opening only slightly larger than 1/2” in diameter to gain entry. It is necessary to carefully inspect the exterior of the house, checking eaves and roof adjoinments, door thresholds and foundation vents, as well as any opening around pipes or wires, to ensure as many entry points as possible are properly sealed. In addition to the exclusion, proper trapping is needed to eliminate the remaining Rats inside the house. It is important NOT to use poisonous bait inside a home for Rats because of the high possibility of the Rat dying inside an inaccessible wall, causing additional pest problems, not to mention horrid odors.