House rats originated in South and East Asia and lived as tree dwellers in warmer regions of the Himalayas. They were spread worldwide by humans on trade routes. Today they are found on all continents except the polar regions. In North and South America, Africa and Australia, however, they are mainly found in coastal regions, usually no further than 200 kilometres inland. Through excavations and genetic analyses, it has been possible to trace the spread of house rats: 5000 - 1500 B.C.: from India via Persia to Egypt; 1500 - 0 B.C.: spread in the Mediterranean region; 0 - 1000 A.D. spread in Northern and Central Europe. From the 15th century worldwide distribution. Since the 18th century, the house rat has been gradually displaced by the newly spreading Norway rat. In Northern and Central Europe, the house rat is becoming increasingly rare. In Germany, the house rat was even protected for a time. Larger populations can still be found in the Mediterranean countries, where the climate is more favourable for the house rat.
In colder regions, the house rat is bound to humans and buildings. In warmer regions, the house rat is found indoors, but also outdoors all year round.
Outdoors, house rats build their nests above ground in sheltered places. In the wild, they can therefore be found in:
The heat-loving house rats like it dry and live in buildings, especially in higher areas. They are not found in sewers. They colonise:
A house rat, also called a roof rat, climbs in the rafters of a garage
Farms in general and any kind of animal husbandry 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.
Ideal habitat for house rats
1. These barns cannot be sealed against rats
2. dense bushes provide nesting sites and hiding places
3. Littered area provides nesting sites and hiding places
4. Water and chicken feed available around the clock
House rats are adapted to life in trees and are excellent climbers, much better than the Norway rat. In case of danger, they usually flee upwards. They can also jump and swim very well. Unlike Norway rats, house rats raise their tails when they run. This makes it easy to distinguish between the two tracks. In the case of the house rat, there are no drag marks from the tail.
They move above the ground if possible. Walkways are marked with urine and faeces. You can recognise heavily used paths by a dark brown smear layer. In buildings, they usually walk along walls or on roof beams. In the dark, rats orientate themselves by means of their whiskers, scent marks and ultrasonic echoes, similar to bats.
Grain silo, open at the top
1: pronounced smear marks on the wall where the rats have been climbing into the silo for years
2: grain contaminated with rat droppings
House rats are highly intelligent and very social animals and usually live in packs of mostly 20 to a maximum of 60 animals. 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, even beyond the territorial boundaries. Pack members recognise each other by smell. When the packs become too large, they split up and some of the rats migrate. Also 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.
House rats forage within a radius of 50 - 100m from the nest.
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 an important role in social and mating behaviour, orientation in the dark and foraging. Thus, tamed rats in Africa have already been trained to search for mines.
Like many other rodents, house 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:
House rats prefer dry and warm places. Nests are mainly built above ground in sheltered places, or in buildings on the upper floors, always in the immediate vicinity of a food source. These nests are usually spherical and have only one entrance. House rat nests have been found as high as 60 metres in treetops. The nests are made of vines, twigs and leaves and padded inside with blades of grass. In and on buildings, scraps of paper, plastic and cloth or wood wool are also used to build the nests.
Occasionally, wooden beams are hollowed out in buildings to make nests.
Rat nest in wall, wall marked with heavy smear marks
In winter and for rearing young, large communal nests are built. Several litters of different ages can often be found there. During the rest of the year, one family always occupies one nest.
House rats are not found in sewers and do not normally make burrows. Burrows are more likely to be found in warmer regions and then in the root zone of trees.
Natural enemies:
Basically, house rats are preyed upon by many predators and birds: cats, dogs, foxes, martens, snakes, birds of prey, owls and many more. However, this only affects outdoor populations. Predators are hardly ever found indoors.
As a rule, house rats are nocturnal to protect themselves from their enemies and spend most of the day in their hiding place. They are mainly active at sunrise and sunset. Only juveniles may also be seen during the day. 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 livestock farms, the rats often orient themselves to the feeding times or the presence times of staff.
Before a group leaves the burrow, a pioneer rat first explores the area and looks out for possible dangers. Only then do the other rats leave the nest to go in search of food.
Man as the enemy:
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, for example, the traps or baits set up are not or only hesitantly accepted. This neophobia is even more pronounced in house rats than in Norway rats. Traps or baits set in bait stations are usually not accepted at all.
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 not 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, it may then become completely behaviourally resistant to traps. Despite numerous rats and many traps set, nothing is caught for weeks and months. For this reason, it is not possible to completely control a large rat infestation with traps alone. This requires a integrated control approach that includes clearing and cleaning measures, securing buildings, waste management and, above all, food deprivation.
House rat inspects trap and camera
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 with 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.
Myths and superstitions about rats:
It is often said that rat packs have tasters. This is not correct. Rather, in every pack there are especially lower-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 an agonising and slow death and should be rejected for animal welfare reasons.
As previously described, house rats actually have scouts for this, which check the surroundings before the rest of the pack comes out of hiding.
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, getting 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.
House rats are also reported to form so-called "rat kings". In the process, the tails become knotted or the animals in the nest stick together. This is said to create formations of 5-20 or even more rats. Since the "rat king" cannot leave the nest, he is fed by the other rats of the pack. There are indeed such museum specimens and even recent films that are supposed to prove the existence of rat kings. So much for the theory. More likely, however, these rat kings were fabricated by humans and belong to the realm of mythical creatures. A rat caught by the tail and threatened with starvation would simply gnaw off its own tail. X-ray examinations of museum specimens have shown that the tails were broken and new bone could be seen at the fractures. So the rat kings must have lived knotted like this for at least a while. But even if rats' tails could accidentally knot, why would the tails be broken? And sure, the other rats could feed the king. But how could they bring the captive conspecifics the water they need every day?
This is what a rat king should look like
House rats are omnivorous, but clearly prefer plant foods such as grains, fruits, nuts, seeds, buds, mushrooms, and bark. In times of need, small animals such as insects, spiders, snails, reptiles, fish, birds' eggs, chicks, mice and carrion are also accepted. When hungry, larger animals such as chickens, lambs or piglets and even babies or bedridden humans are also eaten.
This rat devours bird seed under a bird feeder. Rats love sunflower seeds!
The house rat mainly eats stored food and feed in warehouses and livestock farms. It also recycles waste in residential areas. Due to its preference for fruits of all kinds, it can become a plant pest.
House rats carry food into the nest and store durable items such as nuts and grains in depots near the nest.
House rats absolutely need daily access to drinking water and cannot get the water they need from food like mice. Water sources can be bird baths, leaking water pipes, condensation from air conditioners, drinking bowls from pets, flower pots or irrigation systems. Only in the case of very moist food such as fresh fruit can house rats manage without water.
10-20ml of water and 10-20g of food are needed per day.
House 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 60 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.
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.
A rat infestation can be recognised by droppings, gnaw marks, the smell of urine and noises. If the infestation is more severe, rats can often be observed directly.
An adult house rat produces 40-50 chops a day. Even a few rats can produce literally thousands of chops in a short time. These chops are 10-15mm long, light to dark brown in colour, curved and with pointed ends.
House rats have no fixed toilet places, but constantly shed faecal pellets where they walk and stand, which can accordingly be found in the animals' entire range of movement. This also applies to stored food and feed, which is thus contaminated with harmful germs.
Fresh faeces are lighter, moist, shiny and soft. Older droppings are hard and darker. Rat droppings contain many hairs that are swallowed during grooming.
Rodents like rats have very distinctive incisors that grow back for life. An incisor of an adult house rat is 2mm wide. Bites of rats consist of 2 parallel grooves, up to 4mm wide in total.
With their distinctive gnawing instinct, rats destroy a 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 down teeth when they are overlong.
House rats occasionally hollow out structural timbers, such as roof beams, to make nests in.
The holes that rats bite into the various materials have a diameter of at least 5cm and often have ragged, frayed edges.
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.
House rats mark their walking paths with urine, glandular secretions and faeces. This causes heavily trafficked areas to turn dark and smell strongly. These scent marks 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 walking paths.
Walkways and rat holes are always the best places to set traps!
House rats destroy large quantities of food and feed, not only directly by eating, but also by contamination with hair, saliva, urine and faeces.
House 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 fever, rat typhus, foot-and-mouth disease, swine fever, trichinosis, Lyme disease and many more. Some of these diseases can be fatal. Living in rubbish dumps and stables, house rats come into contact with many germs and spread them over a wide area. Plague outbreaks in the Middle Ages were favoured by house rats and their fleas. Germs are transmitted through contact with the rodents' faeces, urine, saliva and hair. In addition, house rats can carry parasites such as fleas, ticks, mites and tapeworms into human dwellings.
When working with rat traps, (dead) rats or rat faeces and urine, it is advisable to wear gloves.
House rats cause a wide range of damage. They destroy food and feedstuffs, destroy property by gnawing 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. Infestation with house rats can be effectively prevented through the withdrawal of food sources, building sealing, sanitation and waste management.
In autumn, when the fields are harvested and the cold and wet weather sets in, the rats leave their summer quarters and look for a dry and warm shelter in and around buildings for the winter. It is best to catch or drive away the 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 facade or roof area. House rats need an opening of only 2cm 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.
The most important attraction for rats is the availability of food and to a lesser extent water. 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. Only metal and glass can permanently withstand rats' teeth. The most frequent cause of infestation in private gardens is bird food that has fallen on the ground. Avoid excessive bird feeding. Only offer as much dog and cat food as is eaten during the day. Leftover food should be locked away at night. Rubbish must also be stored in a rodent-proof place. Food leftovers do not belong on the compost heap or in the toilet.
If possible, water sources such as leaking pipes, fountains or bird baths should also be eliminated.
Do not provide nesting opportunities for rats. Bulky waste and other rubbish does not contain food, but offers ideal hiding places and nesting opportunities and should therefore be disposed of. House rats also thrive in overgrown green spaces, scrub and ivy growth and can meet some of their food requirements from the plants. Palm trees should be pruned regularly to remove dead fronds.
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 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.
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:
Chicken house with rat infestation, trap placed in the corner along a rat run and secured with a wire rope
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.
Rat traps placed at rat hole on walkways:
1. Passage
2. inverted tray to shield the traps and allow access from the front onlyn
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:
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.
