NORWAY OR BROWN RAT (Rattus norvegicus)

INTRODUCTION:

ratsThe Norway rat is the largest of the commensal rodents and the most common commensal rat in the temperate regions of the world. It not only damages/destroys materials by gnawing, eats and contaminates stored food, but it is also of human health importance as a vector or carrier of diseases. It is thought to be of central Asian origin, but is now of worldwide distribution and found throughout the New Zealand.

 

RECOGNITION:

Adult with combined head and body length (18-25cm), tail length (15-21cm), usual weight about (200-500g) but up to (620g). Fur is coarse, shaggy, brown with scattered black hairs, with underside gray to yellowish white. With muzzle blunt, eyes small, ears small (do not reach eyes) and densely covered with short hairs. Heavy bodied. With a bi-coloured (darker above) scaly tail, shorter than head and body combined. Adult droppings up to (20mm) long, capsule¬ shaped, and with blunt ends.

 

SIGNS OF INFESTATION:

  1. Gnaw marks. New gnawing’s or holes tend to be rough whereas, old gnawing’s are smooth from wear and old holes are often greasy.
  2. Droppings. Fresh droppings are soft and moist whereas, old droppings are dried and hard; adult Norway’s about 3/4″ (18-20 mm) with blunt ends vs. adult roof’s (about 1/2″ (12-13 mm) with pointed ends.
  3. Tracks/footprints. Front foot 4-toed and print is in front of usually longer hind print with 5 toes . Fresh tracks are clear and sharp whereas, old tracks are at least partially obscured by dust.
  4. Rub marks or dark, greasy markings on vertical surfaces. Fresh marks are soft, greasy, and easily smeared whereas, old marks are with the grease dry and flaky.
  5. Burrows. Found in earthen banks, under concrete slabs, and under walls. If active, free of dust and cobwebs. Main opening usually with hard packed soil, rub marks may be visible.
  6. Runways. Consistently follow same paths, usually along walls, stacked merchandise, etc. Active runways with greasy appearance, free of dust and cobwebs, with fresh tracks and/or droppings.
  7. Damaged goods. Norway rats prefer meat, fish, and cereal (dry dog food a favorite) whereas , roof rats prefer fruits, vegetables, and cereals.

 

SIMILAR GROUPS:

(1) Roof rat (Rattus rattus) with muzzle pointed, eyes large, ears large, almost naked tail uniformly colored and longer than head plus body, droppings spindle-shaped with pointed ends. (2) House mouse (Mus musculus) with muzzle pointed, ears large, tail about as long as head plus body, small (14-28g), shorter (head, body and tail (6.5-10.2cm), droppings (3-6mm) long, rod-shaped with pointed ends.

 

BIOLOGY:

Norway rats reach sexual maturity in 2-5 months. Pregnancy lasts an average of 23 days (range 21-25). The young are blind and naked at birth. Hair appears in about 7 days and eyes opening in 12-14 days. They are weaned at about 3-4 weeks. The average number of litters is 3-6 per year (range 3-12), each containing an average of 7-8 young (range 6-22) , but averaging about 20 weaned/female/year. Adults live an average of 6-12 months, but much longer in captivity.

They have rather poor vision and are color blind, but their senses of hearing, smell, touch, and taste are keenly developed. Touch is via their vibrissae or long whiskers. They are good runners, climbers, jumpers, and swimmers.

A Norway rat requires (21-28g) of food and (15-30ml) of water each day, with the water coming from a nonfood source. This result in about 30-180 droppings and 3 teaspoons (16 cc) of urine produced each day.

Historically, the disease most commonly thought of involving rats (roof rat primarily) is plague which is transmitted via fleas leaving an infected rat and attacking man. Fortunately, plague has not been found in rats in the United States for many years. Other transmittable diseases include murine typhus via fleas (also possibly via droppings and urine), infectious jaundice/ leptospirosis/Weil’s Disease via urine in water or food, rat-bite fever via bites, trichinosis via undercooked pork, and food poisoning or Salmonellosis via droppings. Another problem is tropical rat mite dermatitis which is caused by these mites when they feed on humans.

 

HABITS:

Rats are primarily nocturnal in habit and they are cautious. Although they constantly explore their surroundings, they shy away from new objects and changes. Outdoors, Norway rats prefer to nest in burrows in the soil along railroad embankments, stream/river banks, piles of rubbish, under concrete slabs, etc. The burrow will have at least 1 entrance hole and at least 1 bolt-hole or emergency exit which is often hidden under grass, debris, etc.

These are social animals and often many burrows will be located within a given area. An opening of greater than 1/2″ (12 mm) is required for entry into buildings. Indoors, Norway rats usually nest in basements and the lower portions of buildings in piles of debris or merchandise as long as it is not disturbed. Although Norway rats prefer the ground or lower levels of buildings and sewers, on occasion they may be found in attics, on roofs, and in other high places.

Although they will eat practically anything, Norway rats prefer meat, fish, and cereal. If the food material eaten proves to be disagreeable, they are quick to develop food/bait shyness. Once they find an acceptable/preferred food, rats tend to eat their fill at one sitting/place and will return time after time. They almost always require a nonfood or separate source of water. Norway rats will travel about (30.5-45.7m) from their harborage for food and/or water. They will gnaw through almost anything to obtain food and/or water, even plastic or lead pipes.

Once established, Norway rats tend to follow the same route or pathway between their harborage and food and/or water sources. As often as possible, they follow vertical surfaces which their vibrissae or long whiskers can contact. Runways along vertical surfaces will usually include dark rub marks on the vertical surfaces where their oily fur makes contact. Their runway will be free of debris, and outdoors, the grass will be worn away to the bare soil.

 

BLACK, ROOF OR SHIP RAT (Rattus rattus)

INTRODUCTION:

rattusThe roof rat is the smaller of the 2 commensal rats (Norway rat is larger) and the more common commensal rat in the subtropical and tropical regions of the world. It not only damages/destroys materials by gnawing, eats and contaminates stored food, but it is also of human health importance as a vector or carrier of disease organisms. Roof rats are usually thought to be of Southeast Asian origin, and are now worldwide in distribution. In New Zealand, it is more common in the coastal provinces and seaports.

 

RECOGNITION:

Adults with combined head and body length (16-20 cm), tail length (19-25 cm), usual weight (150-250g) but up to (340g). Fur soft, smooth, color usually brown with black intermixed, to gray to black above with underside white, gray, or black. With a pointed muzzle, large eyes, large ears (can be pulled over eyes) and almost naked. Tail is scaly, uniformly dark, and longer than head and body combined. Adult droppings up to (12.5 mm) long, spindle-shaped, with pointed ends.

 

SIGNS OF INFESTATION:

  1. Gnaw marks. New gnawing’s or holes tend to be rough whereas, old gnawing’s are smooth from wear.
  2. Droppings. Fresh droppings are soft and moist whereas, old droppings are dried and hard; adult roof’s about 1/2″ (12-13 mm) with pointed ends vs Norway’s about 3/4″ (18-20 mm) with blunt ends.
  3. Tracks/footprints. Front foot 4-toed and print is in front of usually longer hind print with 5 toes. Fresh tracks are clear and sharp.
  4. Rub marks or dark, greasy markings on vertical surfaces. Fresh marks are soft, greasy, and easily smeared whereas, old marks are with the grease dry and flaky. Swing marks often present around rafters.
  5. Burrows. Not common, but if present they are shallow. They usually nest in or under vegetation.
  6. Runways. Travel routes may not be apparent outside because they may travel along fences or on overhead power or telephone lines. Indoors, they usually move along walls, stacked merchandise, etc. Active runways with greasy appearance, free of dust and cobwebs, with fresh tracks and/or droppings.
  7. Damaged goods. Roof rats prefer fruits, vegetables, and cereal whereas; Norway rats prefer meat, fish, and cereal.

 

HABITS:

Roof rats are primarily nocturnal in habit and they are very cautious. Although they constantly explore their surroundings, they shy away from new objects and changes. Roof rats prefer to nest in the upper parts of structures but may be found under buildings as well as occasionally in basements and sewers. Outdoors , they prefer to nest in higher places such as in trees but may occasionally be found in burrows in or under vegetation around the structure. These are social animals but less so than Norway rats. Several nests may be located within a given area. An opening of greater than (12mm) is required for entry into buildings.

Although they will eat practically anything, roof rats prefer fruits, vegetables, and cereals. If the eaten food material proves disagreeable, they are quick to develop food/bait shyness. Once they find an acceptable/preferred food, rats tend to eat their fill at one sitting/place and will return time after time.

Once established indoors, roof rats tend to follow the same route or pathway between their harborage and food and/or water sources. Runways along vertical surfaces will usually include dark rub or swing marks on the vertical surface where their fur makes contact. Their runways will be free of debris, and outdoors, the grass will be worn away to the bare soil.

 

BIOLOGY:

Roof rats reach sexual maturity in 2-5 months. Pregnancy lasts an average of 22 days. The young are blind and naked at birth, with hair appearing in about 7 days and eyes opening in 12-14 days. They are weaned at about 3-4 weeks. The average number of litters is 4-6 per year, each containing an average of 6-8 young. Adults on an average live 9-12 months.

They have rather poor vision and are color blind, but their senses of hearing, smell, touch, and taste are keenly developed. Touch is via their vibrissae or long whiskers. They are good runners, excellent climbers and jumpers, and if forced, rather good swimmers.

A roof rat requires (14-28 g) of food and (30ml) of water each day, with the water often coming from its food. This results in about 30-180 droppings and 3 teaspoons (16 cc) of urine per day.

Historically, bubonic plague has been associated with the roof rat and its fleas, which move from infested rats to man. Fortunately, plague has not been found in rats in the United States for many years. Other transmitted disease organisms include murine typhus via f leas (also probably vi a droppings and urine) , infectious jaundice/leptospirosis/Weil’s Disease via urine in water or food, rat-bite fever via bites, trichinosis via undercooked pork, and food poisoning or Salmonellosis via droppings. Another problem is tropical rat mite dermatitis which is caused by these mites when they feed on humans.

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