Written by: Helena Kleine
New York City is known to have twice as many rats as people. They cavort in the sewers, subway shafts, parks and dark backyards. And even in major German cities like Berlin, there are estimated to be millions of Norway rats. These rodents are wild animals that, as early as the Middle Ages, sought out the proximity of settlements where food scraps provided a good livelihood. Humans and rats have therefore lived side by side for thousands of years.
Rats are shy, nocturnal creatures that do not pose a threat to humans. Nevertheless, they do not have a good reputation: In the Middle Ages, they were blamed for transmitting the plague - although, strictly speaking, it was the rat flea that was responsible for this. And even today, rats are considered dangerous. Like all wild animals, they can potentially transmit diseases. In Germany and Europe, however, this happens only extremely rarely.
Nevertheless, cities in Germany fear so-called rat plagues, in which the population becomes so large that rats cannot stay in their hiding places and pollute the entire city with feces and urine. If there are a lot of rats, the risk of disease also increases. In addition, many people feel disgusted by the small animals. A rat infestation is not least an image problem.
Once a rat population gets out of control, it quickly becomes a rat plague, because the Norway rat, which lives in cities, multiplies rapidly. A female rat can reproduce all year round and gives birth to a maximum of 15 young per litter, but on average more like four to five. After only two to three months, the young are sexually mature themselves.
Rat populations can theoretically be kept in check by a number of factors. Cities often resort permanently to poison baits, of which a whopping 83 tons are spread in Germany every year - despite ever stricter legal requirements and warnings from the Federal Environment Agency. Even though poison baits are relatively effective when applied correctly, their use is extremely problematic.
The active ingredients of the so-called 2nd generation contain anticoagulants, from which the rats bleed to death internally within 3-7 days. The poisons are effective, but fall under the definition of PBT substances. This means that they are persistent, bioaccumulative and toxic. They break down with difficulty, accumulate in animals and have a toxic effect. This makes them a danger to non-target animals and the environment.
For example, a rat bait can be eaten by pets such as dogs or cats and poison them. In addition, poisoned rats in their days-long death throes are ideal prey for foxes, birds of prey or weasels. And elevated levels of PBT toxins have been detected in all of these animals, especially in regions where a lot of rat poison has been applied.
And last but not least, there is always the risk of bait in sewers being washed away when water levels are particularly high. This is how poisons get into bodies of water and affect the health of fish and other aquatic life.
So whichever way you look at it, rat poison should only be used in an emergency to protect animals, nature and ultimately humans. But how can that work?
The principle of Integrated Pest Management (IPM) is that poisons are used only when all other methods have already been exhausted. The broad base of the IPM pyramid is structural and sanitary precautions. However, if one looks at common practices in urban rat control, little attention is paid to these aspects.
The idea is simple: rats will stay where there is enough food and shelter. Sewers offer great conditions - long distances can be covered quickly, rats are well protected from danger from natural enemies, and even find a tasty treat underground from time to time.
Blocking rats' access to sewers means they lose an important habitat and shelter in the city.
Less habitat = smaller rat population
The rats then have to move to other areas of the city, where they have less chance of survival and are less able to raise young than in the shelter of the underground tunnels. As a result, their numbers are decimated automatically and, above all, permanently.
The perfect entrance and exit to the sewer system for rats is the manhole cover. If you succeed in making manhole covers "rat-proof", the animals will no longer be able to get back underground. This is where "Rat Cap" comes in, a product with which manhole covers can be retrofitted at very low cost.
The idea behind RatCap is quite simple: The device is attached to the dirt trap in a manhole and thus seals the gap between this dirt trap and the manhole. This way, rats that are in the sewer can't make it out; and rats that are above ground can't get in.
Footage from our PestCam, which is also used in manholes to better understand the behavior of rats in the sewer system, showed that rats leave the sewer system primarily at night to forage in residential neighborhoods and parks. At dusk at the latest, they return underground via the ladder steps in the gully.
RatCap is a very simple solution that blocks exactly this path, thus greatly reducing a rat population within six to 24 months.
Rat control with poison can be thought of as an expensive lease on an apartment where things are constantly breaking. Fuses blow when you use the stove and the oven at the same time, the water pressure in the shower is much too weak and the insulation is not the real thing either, so the heating costs go through the roof. If you fight rats with poison, you have to pay monthly for new bait, which in case of doubt doesn't even end up where it's supposed to: in the rat's stomach. And despite the costs and ongoing efforts, you never really get a handle on the situation.
The alternative would be to build your own, modern, new house. The effort is initially higher and there are certain costs. But once the work is done, the builder can sit back and benefit from this investment for many years to come. It's a similar story with construction measures that reduce the habitat for rats in cities. Once properly implemented, the costs pay for themselves very quickly. In addition, there are large gains for the environment.
RatCap is an example of structural measures that cities can take to control rats. With a few simple steps and the use of mounting clips, the solution is quickly installed. It lasts for many years and costs less in the long run than baiting with poisons. If you are interested in RatCap for your urban rat control, just contact us!
Would you like to learn more about the use of RatCap in practice? The Berliner Wasserbetriebe report on their successes in our case study.