Norway ratNorway rat

THE NORWEGIAN RAT

Habitat

Norway rats originate from north-east Asia (southern Siberia and northern China). There they live predominantly in forests and bushy areas. They were spread worldwide by humans from the 18th century onwards, mainly by ships. Due to their adaptability, Norway rats can be found all over the world, except for Antarctica. Norway rats live mainly in the vicinity of humans. In the tropics, Norway rats are only found in settlements, especially near the coast.

As far as possible, rats build their nests in burrows.

  • on streams, rivers and other water bodies
  • on embankments and in dense bushes
  • under piles of straw, wood or stone slabs
  • under foundations of buildings

Rattenbau unter einem Garagenfundament

Rat hole under a garage foundation

In buildings:

  • attics
  • garages
  • garden sheds
  • cellar rooms
  • dog houses, chicken coops and other animal sheds
  • in the sewers
  • void spaces in buildings, e.g. hollow ceilings, walls and floors 
  • corners in cluttered or littered areas
  • between stacks of goods 
  • under cupboards and in furniture voids
  • under kitchen furniture and appliances
  • in storage boxes and cartons 

Rats love the sewers. Living here offers them many advantages:

  • safety: no or hardly any natural enemies
  • pleasant temperatures all year round
  • there is plenty of food in the sewage system that has been disposed of down the toilet.
  • the rats can move over long distances invisibly and protected.
  • there are numerous possibilities for leakage from the sewer system to the surface or into buildings due to defective pipes and connections.

 

Inspection shaft, with signs of rat activity: rat droppings, sand and gravel testify to the presence of rats.

 

Wall opening for drainage pipe, next to rat hole

Farms in general and any kind of animal husbandry in particular are strong attractions for rats. There is plenty of food in the form of animal feed or stored crops, there are lots of good hiding places and the farm buildings and stables often cannot be rodent-proofed.

 
Grain silo, open at the top; grain spilled on the floor and special feed in open paper bags, a set table for rodents.

The same silo, seen from above: 
1: pronounced smear marks on the wall where the rats have been climbing into the silo for years
2: grain contaminated with rat droppings 

 

A rat in a chicken coop. They eye each other with mutual respect, are cautious and avoid direct confrontation. However, rats eat not only chicken feed but also eggs and sometimes a chick.

 

Rat holes in the floor of a chicken coop

Way of life / Behaviour

Norway rats are good swimmers, divers, burrowers, climbers and jumpers. However, they mostly move on the ground. In buildings, they run mainly along walls. Running paths are marked with urine. In the dark, rats orient themselves by means of their whiskers, scent marks and by means of ultrasonic echoes, similar to bats. 
Rats are highly intelligent and very social animals. They usually live in small family groups of two parents and their offspring, which can quickly grow into large packs. However, one can also often observe roaming individuals, mostly males. How many rats live in one place or how large a pack becomes depends mainly on the food supply. 
Rat packs have fixed territories and defend them aggressively against other rats. Pack members recognise each other by smell. When the packs become too large, they split up and some of the rats migrate. Furthermore, young, lower-ranking males often migrate after reaching sexual maturity in order to escape the oppression of dominant pack members and to develop their own territory.
Despite their territorial behaviour, individual rats sometimes undertake dangerous nocturnal migrations of several kilometres to explore the surroundings for new food sources or free territories. In an emergency, a whole pack can migrate to a new location. Triggers for migration can be, for example, lack of food but also high losses due to successful pest control. It is the experienced adults who have a plan B. They notice when living conditions deteriorate too much and then bring their offspring to safety.
Rats are very nasal animals and can smell much better than they can see. Their sense of smell is as highly developed as that of dogs. The sense of smell plays a major role in social and mating behaviour, orientation in the dark and foraging. For example, a certain species of rat (Gambian giant hamster rat) has already been trained to search for mines.
Like many other rodents, Norway rats can only perceive colours to a limited extent, but they have excellent night vision and can also detect infrared light. Therefore, they also perceive the infrared light of wildlife cameras and avoid staying in the cone of light of the cameras.

Nests
Rat burrows are not very deep and always have several exits for protection from predators such as weasels, so that a free escape route is always available. The openings have a diameter of 6-10 cm. Often, clearly visible running paths lead away from the holes. The burrows are usually made in the immediate vicinity of the food source. Rats forage within a radius of 50m to 400m from the nest. The nests are padded with soft materials such as grass, hair, feathers, leaves and moss, but also scraps of paper, plastic, cloth or wood wool.

 

Rat burrow under chicken coop
Heavily frequented main entrance on the left
Right: little used side entrances

Natural enemies:
Rats serve as prey for many predators and birds: cats, dogs, foxes, martens, snakes, birds of prey, owls and many more. As a rule, Norway rats are nocturnal in order to protect themselves from their enemies. However, this can vary greatly depending on local conditions. For example, the availability of food, or when there is least danger, also play a role. In the case of rat infestations in school playgrounds, the normally nocturnal rats come out during the day at the end of the breaks. This is because the pupils have left and the freshly thrown away break time sandwiches are ready. 

Humans have also hunted rats for many millennia. Initially for consumption, later also to prevent damage and the spread of disease. To this day, rats are considered a source of meat in many cultures. Because of the intensive stalking by humans over such long periods of time, rats have developed different strategies to recognise and avoid traps and poison. 
 

These rats are caught alive by hand by children in The Gambia and sold for the equivalent of €0.50 as a soup garnish. 

For example, rats have an innate shyness towards unknown food and unfamiliar objects (neophobia). This makes the control of rats difficult because, the traps or baits set up are not or only hesitantly accepted.
Experienced rats have often had contact with traps. They have seen dead conspecifics lying in traps, have been present when a family member was killed by a trap or have triggered a trap themselves and survived. The latter happens not so seldom when traps of inferior quality are used. Such an animal will never enter a trap again under any circumstances. Rather, it will warn all other pack or family members or even bite them if they disobey when traps are set. In the worst case, a whole pack may then become completely behaviourally resistant to traps. Despite numerous rats and many traps set, nothing will be caught for weeks and months. For this reason, it is not possible to completely control a large rat infestation with traps alone. This requires an integrated control approach that includes clearing and cleaning measures, securing buildings, waste management and, above all, food deprivation.
Just as rats warn each other of traps, they also warn each other of poison baits. There is a strict hierarchy among the male rats of a pack. The higher-ranking rats can forbid other members of the pack to eat poison bait and enforce this physically if necessary. 
Poisoned rats sometimes return to the place where they ingested the poison to die. The carcass then serves as a warning to the other pack members about the poison bait.
It is often said that rat packs have tasters. This is not correct. Rather, in every pack there are especially low-ranking animals with less access to food. These are hungrier and most likely to accept new food sources, such as poison bait, and are watched by the other rats. If nothing happens, over time the other rats will also accept this new food source. If it turns out badly for the "taster", the site will be marked by smell by the other rats and the baits will be avoided. Therefore, instant poisons do not work well with rats. The poison baits commonly used today only have a lethal effect after a few days. Ideally, all animals will have eaten the bait before the first signs of poisoning appear in the pack and the rats would be warned. Due to the delayed onset of action, these poison baits are more effective, but cause a painful and slow death and should be rejected for animal welfare reasons.
Another superstition is that rats, if cornered, would attack a human. This is also not true. A cornered rat will rather try to run between your legs, coming very close to the attacker. However, under no circumstances should you catch a rat with your bare hand. Rats can bite very hard and would do so in self-defence. 

 

A cornered rat. The distance to the photographer was about one metre. The rat is visibly stressed and ready to jump away: the ears are laid back, the tail covered and the toes spread. But there has been no attack on the photographer.

Rats as laboratory and domestic animals: 
The laboratory rats used since the 17th century until today are descendants of Norway rats. They are descended from a mutant albino rat. The pet and food rats (Rattus norvegicus domesticus) are also descended from Norway rats. 
Sometimes pied animals occur in populations of wild rats. These are abandoned or escaped pet rats that have joined wild packs, or their offspring.

 

Tame pet rat

Nutrition

Rats are omnivores, but clearly prefer plant foods such as cereals, fruits, nuts, seeds, buds, dog food, cat food and bird food. However, they also feed on small animals such as insects, spiders, snails, reptiles, fish, birds' eggs, chicks, mice and carrion. Under extreme conditions, i.e. very heavy infestation and little food supply, larger animals such as chickens, lambs or piglets and even babies or bedridden humans are gnawed on.

This rat is eating birdseed under a bird house. Rats love sunflower seeds!
In Europe, the Norway rat feeds mainly on stored food and feed in warehouses and animal husbandry. It also recycles waste in settlements, e.g. in the sewage system or from waste containers and in waste disposal plants. 
Norway rats need daily access to drinking water and cannot get the water they need from food like mice. 
30-60ml of water and 15-30g of food are needed per day.

Rat family, dropped into a grain silo from above and now trapped.

Reproduction

Norway rats are characterised by a high reproduction rate. Under favourable conditions, they can reproduce all year round. Thus, a rat family can grow to a pack of over 100 animals within one season. All females of a pack give birth to their young at the same time, so that any orphaned young can be suckled by the other mothers.
 

A litter of ten naked and blind baby rats.

  • Litter size: 8 - 12 young per litter
  • Number of litters: 4 - 7 per year
  • Sexual maturity: 2 - 3 months
  • Gestation period: 22 - 24 days
  • Breeding season: Indoors all year round; outdoors from spring to autumn.

In large packs, there is a control of reproduction. When the population becomes too high and stress and aggression increase, a hormone is released that prevents reproduction and triggers higher mortality.

Facts

  • Scientific name: Rattus norvegicus
  • Other names: Brown rat, common rat, harbour rat, water rat, sewer rat
  • Colour: Normally grey-brown, varying from pure grey to reddish brown to black-brown, ventral side lighter, beige to light grey; 
  • Weight: 170 - 500g; 
  • Body length: 18 - 26cm
  • Tail length: 14 - 21cm; slightly shorter than the body, naked with rings
  • Body: Compact, rectangular skull, blunt muzzle.
  • Ears: Relatively small, at the very back of the head
  • Eyes: Relatively small, protruding black eyes
  • Life expectancy: 1 - 2 years, usually less than 1 year due to heavy stalking by predators.
  • Rat faeces: 10-30mm long with blunt ends; dark coloured; often deposited in piles 

Manifestations and Damage

Overview

A rat infestation can be recognised by droppings, gnaw marks, the smell of urine and noises. Outside, the large rat holes in the ground are conspicuous. If the infestation is more severe, rats can often be observed directly. 

Rat Faeces

An adult Norway rat produces 40-50 chops a day. Even a few rats can produce literally thousands of pellets in a short time. These droppings are 10-30mm long, dark coloured and spindle-shaped, with blunt ends and one end thicker than the other. Therefore, rat droppings are probably the most obvious sign of a rat infestation. Norway rats always deposit their droppings in piles in the same places. Fresh droppings are black, shiny and soft. Older droppings are hard and lighter in colour. Rat droppings contain many hairs that are swallowed when grooming.

Gnaw marks

Rodents like rats have very distinctive incisors that grow back for life. An incisor of an adult rat is 2-3mm wide. Bites of rats consist of 2 parallel grooves, about 4mm wide in total.

With their distinctive gnawing instinct, rats destroy a wide variety of materials such as packaging, textiles, insulation materials, cables, pipes, wood, plastic, bricks, aluminium, copper and even cast iron. They use their strong cutting teeth to open food containers, extract nesting material, enlarge loopholes or simply grind them down when they are overlong. The holes that rats bite into the various materials have a diameter of at least 5cm and often have jagged frayed edges. 

Earthmoving, Burrows & Rat Holes

Their burrowing activity and the construction of earthworks also repeatedly cause damage to sewage pipes, subsidence of pavements and holes in dykes and dams.

Sounds and smells

When rats are active, they make noises by gnawing or running around, e.g. in hollow spaces of ceilings. As they are nocturnal, these noises can be particularly disturbing. However, it is difficult to distinguish whether these noises come from mice or rats. If the infestation is more severe or lasts longer, a pungent urine or ammonia odour will develop. Cats and dogs often show the places where rats run or hide by excited sniffing, exploring and scratching.

Walkways and smear marks

Norway rats mark their paths with urine and glandular secretions. This causes heavily frequented areas to turn dark and smell strongly. These scent trails serve as orientation in the dark. In addition, areas that are regularly walked on by rats can be easily recognised. There is no dust, leaves or other dirt on the paths.


Walkways and rat holes are always the best places to set traps!

Stock damage

Norway rats destroy large quantities of food and feed, not only directly by eating, but also by contamination with hair, saliva, urine and faeces.

Damage to health

Norway rats are harmful to health because they can be infected by a variety of pathogens that can also be transmitted to humans or farm animals, such as plague, salmonella, rat-bite disease, typhoid, cholera, dysentery, SARS, Hanta fever, rat spotted fever, foot-and-mouth disease, avian flu, swine fever, trichinosis, toxoplasmosis, tularaemia, and many more. In total, there are thought to be about 120 diseases that can be transmitted by rats. By living in sewers, on rubbish tips and in composting plants, combined with long migrations into settlements or stables, Norway rats come into contact with many germs and spread them over a wide area. The germs are transmitted through contact with the rodents' faeces, urine, saliva and hair. In addition, Norway rats can carry parasites such as fleas, ticks, mites and tapeworms into human dwellings.

Management and control measures

Conservation status: Norway rats are not protected in any country and may be controlled at any time

Prevention

Norway rats cause a wide range of damage. They destroy food and feed, destroy property by gnawing and burrowing, and transmit pathogens to humans, domestic animals and livestock. In the following chapter, methods for prevention and control are presented. 

Rats settle when favourable conditions such as a good food supply or hiding places are available. Under such circumstances, mass reproduction occurs quickly. It is best to prevent this in advance.
Autumn, when the fields are harvested and the cold, wet weather sets in, is the best time to take action against rats. They leave their summer quarters and seek dry and warm shelter in and around buildings for the winter. It is best to catch or drive away rats before they have taken up residence in buildings.

Rats migrate e.g. through open or poorly closing doors and gates, but also through cellar windows, light shafts, air supply openings, pipe penetrations, cable ducts, cooling and ventilation systems or other openings in the façade. Rats need an opening of only 2-3cm to enter a building. Therefore, there are often many suitable access points along the building. To reliably keep rats out, all access points should be closed as far as possible. 

SWISSINNO Rodent Stop Steel Wool is a quick and easy fix to plug wall openeings, holes and cracks.

Another important access is the sewer system. It happens again and again that a manhole cover is missing, a dead branch has not been closed or a drain pipe is damaged and rats have direct access into a building here. If there is an infestation of rats inside buildings, all connections should be checked and repaired if necessary. In very rare cases, it has also happened that rats have entered a building even when the sewage system is completely intact via the toilets. In this case, a "rat flap" can be installed on the main drainage pipe.

The most important attraction for rats is the availability of food. The all-important preventive measure is therefore the deprivation of food sources: 
Do not store food, pet food and seeds in bags or boxes, but in rodent-proof containers. The most common cause of infestation in private gardens is bird food that has fallen on the ground. Avoid excessive feeding of birds. Rubbish must also be stored in rodent-proof containers. Food scraps do not belong on the compost heap or in the toilet. Only metal and glass can permanently withstand rats' teeth.

Do not provide nesting opportunities for rats. Bulky waste and other rubbish does not contain food, but it provides ideal hiding places and nesting opportunities and should therefore be disposed of.

The action radius of a rat pack can extend over several properties. In other words, the actual source of infestation may not be on one's own property. When searching for the causes of infestation, the neighbouring properties should always be included in the considerations, as far as possible.

Ultrasonic rodent repellers

Ultrasonic rodent repellers are suitable for scaring away rats and preventing them from entering buildings. With SWISSINNO devices, the high-frequency sound is constantly changed to prevent the rodents from getting used to the sound.
It is important to note that ultrasound does not propagate through walls. Therefore, for good effectiveness, ultrasound units must be placed in all affected rooms.
However, if an infestation already exists, the sole use of ultrasonic rodent repellers is not sufficient to get rid of the rats. These devices should always be used as part of an integrated pest control strategy. Food deprivation, clearance and cleaning measures, closure of access routes, traps and ultrasonic rodent traps are used together. 
 

Trapping

With rat traps you can control rats without poison and in a humane way. SWISSINNO rat traps are robust, precise, animal welfare compliant and can be used many times. Great advantages of rat traps are the reliable proof that the rat has been caught and the fact that the dead rats can be disposed of. If poison baits are used, there is no simple and clear control of success, because the dead rats are often not found, but decompose (smell, maggots!) in inaccessible places.
  
There are 3 types of rat traps that are commonly used: Snap traps, live traps and electronic traps.

The following table gives an overview of the different SWISSINNO rat traps:

Rats are not just big mice. They are fundamentally different in behaviour. Mice are easy to catch, but rats are not. Rats have an innate shyness towards traps and are generally very suspicious. They are also social animals that learn quickly from each other. You have to be very careful when trapping if you want to be successful. Any mistake will lead to trap shyness, in the worst case for the whole pack. Individual rats can still be caught well with traps. However, in the case of a larger infestation, comprehensive measures are necessary. It is not enough to simply set up traps.

Trapping - tips from the pros:

  • Before setting traps, remove all traces, droppings and urine. Clean up the infested area. This disturbs and confuses the rats and makes them less suspicious of the traps. If everything is clean, it is also easier to determine where rats are still active in the course of the control.
  • The most important reason why rats settle in a place is a rich food source. It is essential to eliminate all food sources. Traps are hardly accepted at all as long as the usual food is available. 
  • Inferior traps do not catch reliably. Up to 30% of the rats escape more or less injured, are then trap-shy and can no longer be caught. The affected rats "communicate" this to their offspring and other pack members, so that a whole population can very quickly become trap-shy. Only high-quality traps like SWISSINNO rat traps are effective and animal welfare-friendly.
  • Always check traps for proper function before use, especially for smooth release and good spring force. Do not use traps that cannot be tensioned or released well. 
  • Wear gloves when working with traps. The reason is not human smell. Rats in and around buildings do not shy away from human smells. The use of gloves is recommended for hygienic reasons. Rats, whether dead or alive, can transmit dangerous diseases through contact with fur or body fluids.
  • It is better to set more than one trap, even if you suspect only one rat. If there are several rats, more traps should be set accordingly. The distance between the traps should be a maximum of 10 m.
  • Good placement of traps is key to successful trapping. Traps should be placed in the rodents' walking paths. Droppings and smudges indicate frequently used walking paths.

Chicken house with rat infestation, trap placed in the corner along a rat run and secured with a wire rope

  • Traps are best placed on walls or in corners and not somewhere in the middle of the room.
  • It is recommended to tie the traps with a string. Trapped rats can carry away the trap before they die. In the open air, predators or cats always carry away trapped rodents along with the trap.
  • Traps must stand firmly on the ground. Rodents shy away from traps that move or make noise when touched. A secure stand of the trap results in a precise strike and prevents foul or failed catches.
  • Rat traps pose a risk to children, pets and wildlife such as birds and hedgehogs. If pets have access to the trapping areas or traps are set outdoors, the traps should be covered or placed in trap tunnels. This keeps other animals away from the traps.

Rat trap set outside:
1: treaded rat hole
2: Wood placed underneath so that trap stands straight and firm
3: The whole thing was covered with the tarpaulin so that no other animals could get to the trap.

  • Set traps must be checked at least once a day. Carcasses should be disposed of before they become a hygiene problem. In case of a incomplete catch, the rats must be killed. Traps that are not doing well can be relocated. If necessary, traps must be re-baited or re-tensioned. 
  • Live traps must be checked minimum every 12 hours.
  • If in the course of control traps are triggered but empty (so-called failed catches) it is recommended to switch to another trap model. The best trap for rats is the SuperCat PRO rat trap. With this model, failed catches or imperfect catches are virtually impossible. 


Rat traps placed at rat hole on walkways:
1: Passage
2: inverted tray to shield the traps and allow access from the front onlyn

  • The SWISSINNO rat traps are baited with a special peanut butter. Replacement bait syringes are available separately. The bait's attraction range is no more than 1 to 2 metres. Rats are not attracted by the bait from a greater distance or from outside the building.
  • "Pre-bait": it is essential to place a small amount of bait, no more than a pea-sized portion, in front of the trap. This helps to overcome the rats' mistrust.
  • If the peanut butter baits are not accepted, try unshelled sunflower seeds or smoked mackerel instead.
  • You can try to get the rats used to certain feeding places by feeding them. If the rats then accept food well at these places, you can set traps there and use the familiar food as bait. This habituation can take several weeks!
  • You can keep the traps open when cocked with cable ties or tape so that they do not snap shut and offer food in the traps. When the rats have become accustomed to the traps as food containers, you can arm the traps. This can take several weeks!
  • The smell of a dead rat from the last catch does not repel other rats. On the contrary, used traps are more attractive to rats. However, blood from other rats causes trap shyness. If traps need cleaning, use warm water and a soft brush, but no detergent.
  • The sight of a dead conspecific in a trap can lead to trap shyness in the other pack members. Frequent (several times a day) trap checks or trap detectors (preferably online) can help to avoid this learning effect.
  • If there are indications of the presence of legally protected species, such as dormice, it is recommended to contact the local authorities before starting control measures. Measures already in progress must be halted until clarification is obtained. The use of live traps must also first be approved in the case of protected species.

Poison bait

To date, poison baits are a fast and reliable method of rat control. SWISSINNO nevertheless advises against the use of poison baits for several reasons:

  • Poison baits endanger the environment, children, pets, livestock and wildlife.
  • Poison baits cause a slow and agonising death. After ingesting the poison, it takes several days for the rats to die.
  • When poison baits are used indoors, the rats often die in inaccessible places and the carcasses cannot be disposed of. This causes odour nuisances and infestations of carrion flies and maggots that last for weeks. Later, the dried carcasses serve as a food source for other pests such as clothes moths, bacon beetles, fur beetles and carpet beetles for years.

However, if a rat infestation cannot be eliminated despite the best trap application and all flanking measures, the use of poison baits should be considered.

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