The 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 Uk.
Adult with combined head and body length 7-9.5″ (18-25 cm), tail length 6-8″ (15-21 cm), usual weight about 7-18 oz (200-500 g) but up to 20.5 oz (620 g). Fur 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 scaly tail bicolored (darker above), shorter than head and body combined. Adult droppings up to 3/4″ (20 mm) long, capsule-shaped with blunt ends.
SIGNS OF INFESTATION
Gnaw marks. New gnawings or holes tend to be rough whereas, old gnawings are smooth from wear and old holes are often greasy.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.
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.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. 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. 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. Damaged goods. Norway rats prefer meat, fish, and cereal (dry dog food a favourite) whereas, roof rats prefer fruits, vegetables, and cereals.
Roof rat (Rattus rattus) with muzzle pointed, eyes large, ears large, almost naked tail uniformly coloured and longer than head plus body, droppings spindle-shaped with pointed ends. Most native rats and mice have hairy tails, hairs short or long, or if the tail is almost naked, it is also annulate (appears to be of ringlike segments).
Hair appears in about 7 days and eyes open in 12-14 days. They are weaned at about 3-4 weeks and reach sexual maturity at 8-12 weeks. The average number of litters is 3-6 per year (range 3-12), each containing an average of 7-8 young (range 4-22), but averaging about 20 weaned/female/year. Adults live an average of 5-12 months in towns and cities, but much longer in captivity.
They have rather poor vision and are colour 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 (documented record is 1,300 ft or 400 m across open ocean).
A Norway rat requires 3/4-1 oz (21-28 g) of food and 1/2-1 oz (15-30 ml) of water each day, with the water coming from a nonfood source. This results in about 30-180 droppings and 1/2 oz/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, cowpox virus (CPXV) via direct contact, trichinosis via undercooked pork, and food poisoning or Salmonellosis via droppings.
Another problem is tropical rat mite dermatitis that is caused by these mites when they feed on humans.
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.
Norway rats are opportunistic feeders and although they will eat practically anything, they 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 in one or two visits and will return time after time; if the area of food is constantly disturbed, they may require several return visits to get their fill.
They almost always require a non-food or separate source of water. Norway rats will travel about 100-150 ft (30.5-45.7 m) from their harbourage for food and/or water; in urban areas the average home range is about 25-100 ft (8-30.5 m). They will gnaw through almost anything to obtain food and/or water, even plastic or lead pipes.
Norway rats typically forage and feed at dusk and again prior to dawn, although they will forage several times each night and during the daytime. If the area is quiet and undisturbed, daytime activity may or may not indicate overpopulation. They do carry off food to less disturbed areas for consumption, or to hoard.
Once established, Norway rats tend to follow the same route or pathway between their harbourage 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.
The house mouse is the most commonly encountered and economically important of the commensal rodents, the Norway and roof/black rats being the other two. House mice are not only a nuisance, damage/destroy materials by gnawing, and eat and contaminate stored food, they are also of human health importance as disease carriers or vectors. It is thought to be of Central Asian origin, but is now of worldwide distribution and found throughout the UK.
Adult with head and body length 2.5-3.75″ (6.5-9.5 cm), tail length 2.75-4″ (7-10.2 cm), weight about 0.5-1.1 oz (12-30 g). Fur smooth, colour usually dusty grey above and light grey or cream on belly (some mice light brown to dark grey above), but fur colour varies considerably from area to area or location to location regardless of living habits. With muzzle pointed, eyes small, incisors ungrooved, ears large with some hair. Feet short and broad. With a uniformly dark, scaly, semi-naked tail. Adult droppings 1/8-1/4″ (3-6 mm) long, rod-shaped, with pointed ends,
Pregnancy lasts an average of 19 days (range 18- 21). The young are blind and naked except for vibrissae (long whiskers), and are weaned at about 21 days (range 3-4 weeks). The average litter size is 6 (range 5-8), with about 8 litters per year, but averaging 30-35 weaned/female/year.
Therefore, a female can have a new litter about once every 40-50 days. More than 1 litter may be present in the nest at one time. Life expectancy is normally less than 1 year, but mice have been known to live as long as 6 years. Mice have keen senses, except for sight because they cannot see clearly beyond 6″ (15 cm) and are colour blind.
They are excellent climbers and can run up most roughened walls. Mice can swim but prefer not to do so. They can jump 12″ (30.5 cm) high and can jump down from about 8 ft (2.5 m) high without injury. Mice can survive and thrive in cold storage facilities at 14°F (-10°C).
They can run horizontally along pipes, ropes, and wires. A mouse requires about 1/10 oz (2.8 g) of dry food and 1/20 oz (1.5 ml) of water (normally obtained from food) each day and produces about 50 droppings each day. Over a 6-month period, a pair of mice will eat about 4 pounds (1.8 kg) of food, produce about 18,000 droppings, and void about 3/4 pint/12 oz. (355 ml) of urine.
The most common way mice transmit disease organisms is by contaminating food with their droppings and/or urine. The most threatening organism spread by mice is Salmonella, a cause of food poisoning, spread via droppings. Other transmittable organisms include tapeworms via droppings, rat-bite fever via bites, infectious jaundice/leptospirosis/Weil’s Disease via urine in food or water, a fungus disease (Favus) of the scalp either by direct contact or indirectly via cats, plague and murine typhus via fleas, Rickettsial pox via the mite Liponyssoides sanguineus (Hirst), lymphocytic choriomeningitis via droppings, and possibly poliomyelitis (polio).
Another problem is house mouse mite dermatitis which is caused by these mites when they feed on humans.
All mature mice tend to show aggression towards strangers of either sex that enter their territory, which is marked with urine. Territory size varies but it is usually relatively small. If food and shelter are plentiful, they may not travel more than 4-5 feet (1.2-1.5 m) from their nests.
Mice are inquisitive. During the daily territorial patrol, they will explore anything new or changed, and establish new travel routes if needed. Mice are nibblers and eat only small amounts of food at any one time or place. Although mice will eat many kinds of food, seeds and insects are usually preferred.
They are opportunistic feeders and should one food disappear, they will readily switch to another food. There are 2 main feeding periods, at dusk and just before dawn, with many other “mini” feeding times in between. They will sample new foods but return to the old food unless the new food is preferred.
Required moisture is normally obtained from their food but they will take free water when available, especially when feeding on high-protein food. When given a choice, they prefer sweetened liquids over plain water.
Their preferred nesting sites are dark, secluded places where there is abundant nesting material nearby and little chance of disturbance. Nesting materials include paper products, cotton, packing materials, wall/attic insulation, fabrics, etc. Mice are nocturnal in habit. They require an opening of greater than 1/4″ (6 mm) to gain entry.
In rural and suburban areas, the house mouse lives outdoors in wooded areas, fields, croplands, yards, etc., where they build their nest in vegetative debris, natural cavities, burrows, etc. Here they feed on seeds and insects. Since the house mouse cannot hibernate, in temperate areas they seek shelter as the weather cools and their food sources disappear.
Around structures, they follow warm air currents and food odours coming out through door thresholds, utility line entrances, etc. into a suitable site. If the entrance has been marked by previous mice, it’s just that much more attractive. In urban areas, they commonly come in from other structures via utility connections, or from other parts of the same structure. In commercial structures, mice are commonly also brought in with supplies and/or equipment.