Latin: Rattus
Rats are probably the most well-known pest, and historically the rat has been blamed for much misfortune. The rat is known as an infection transmitter, a cunning and unwelcome guest, and a plague all over Europe. In Denmark, the problems are mainly caused by the brown rat, Rattus norvegicus. This type of rat is also called a wandering rat because it wanders around. In rare cases, it may be the black rat, the house rat, which is known as Rattus rattus.
Appearance
Most often it is the brown rat you encounter if you encounter rats at all. This is because the brown rat has migrated into the black rats’ territory over the last few centuries. The brown rat obviously has a brown coat, but the shade can vary. Some brown rats are darker, and some are grayish. The stomach can be whitish or greyish. An adult rat is 45 cm long, but 20 of these are the tail. The tail of the brown rat is slightly shorter than the body.
Male rats are often larger than female rats. A male rat typically weighs between 250 and 300 g, but they can be much larger. The largest captured rat ever found in Denmark was a wild male rat of 545 gram – over 0.5 kg.
The excrement of the brown rat (Rattus norvegicus) is usually 2.0 – 2.5 cm long, blunt at one end and shiny black.
The house rat, or the black rat, is slightly smaller than the brown rat. They are between 16 – 23 cm long, and their tail is between 18-25. The house rat’s tail is, unlike the brown rat’s, longer than the body. The excrement of the house rat is usually 1 cm long, and more curved than the excrement of the brown rat.
Biology and behavior
Rats live together in nests. Here they can reproduce all year round if the temperature is warm enough. They multiply quickly inside buildings, where there is heating. The average female rat gives birth to three to five litters each year, and each of these litters contains of 4-12 rats. A female rat is pregnant for about 22 days, just under a month. The sexual maturity of the individual rat depends on weight and age. Typically, a rat will be sexually mature at three months, where it weighs 150 grams.
The rat makes nests of a variety of soft material. These are typically paper, plastic, sack material, and even straw. Rats can eat pretty much anything, but they need water on a regular basis, unlike mice, which almost never need water, but the mice are pickier.
Damage
Rats can cause a lot of damage to furniture, homes and of course food stuff. A rat can eat a lot, and do a lot of damage, as they like to gnaw in different parts of the building, which in the worst-case scenario can create fire hazards, when they chew on wires and the like. A lot of value can be lost, if you do not put a stop to the rats’ movement in the house or building.
One of the major threats from rats, is that they are an infectious transmitter. Rats, along with mice, are one of the biggest culprits when it comes to spreading salmonella bacteria, leading to food poisoning. Rats also transmit Weil’s disease through their excrement, which is dangerous as Weil’s disease is fatal.
Prevention and pest control
There are several options for controlling the rats. According to the Ministry of the Environment and Energy’s Executive Order no. 611, all municipality must take care of rat control, but it is also up to the individual homeowner to secure his home against rats. If you live in an urban zone, it is important that you report rat problems to your municipality. In land zones, however, a rat controller will inspect the property twice a year.
To prevent rat problems, use common sense. Close all cracks and holes larger than 12 mm with metal nets, metal plates or other material that the rats cannot gnaw through. Do not leave doors and windows open. Remove plants along buildings as they create good passageways for the rat. Make sure there is no food and water available for the rats. This can be both bird and animal feeding, open rubbish bins and open compost piles.
Detection of rats
Since rats are such a common problem in Denmark, many suspect rats, even though it may be mice that create the problems. Fortunately, there are a few ways to determine if you have rats or mice in your home. If you get a glimpse of a rat that seems a little small, it could be a rat cub. You can recognize a rat by its hairless, bald tail. If you are looking for paw prints, prints from a rat will generally be much larger than from a mouse, up to two cm in length. Rats paw imprint has a more prominent shape than the mouse’s reasonably light imprint.
"Pests in House and Home"
"Bed Bugs - Bites, Stings and Itches"
"Food Pests"
"Husets dyreliv" (Insects Around the House - Only danish)
"Skadedyr i træ" (Timber Pests - Only danish)
"Stuefluen" (Common Housefly - Only danish)