Why are rats the “beneficiaries” of floods?

Produced by: Science Popularization China

Author: Bingbingbang (Institute of Zoology, Chinese Academy of Sciences)

Producer: China Science Expo

Floods are one of the most important natural disasters that affect the safety of human life and property. Flood disasters that have occurred in history have claimed the lives of millions of people. When a flood comes, humans must not only escape from the flood, but also be prepared to defend against and fight against diseases and epidemics that may occur after the flood. So, why do floods cause various diseases?

After the flood, various bacteria and viruses breed, and the number of insects and rats increases rapidly. As important carriers of bacteria and viruses, insects and rats spread bacteria and viruses further. In this way, insects and rats and the bacteria and viruses they carry begin to run rampant, thus threatening and endangering human daily production and life.

Some of you may be surprised to see this: the flood was so fierce, but why did the number of rats increase? Don't worry, today we will talk about this question in detail: why do the number of bacteria, viruses, insects and rats increase after a flood?

Floods

(Photo source: Veer Gallery)

"Resource transfer" between old, weak, sick and disabled mice and healthy adult mice

When a flood strikes, not only human lives are washed away, but also lives of other species, including insects and mice. Insects and mice also have their own population age structure, including young individuals, adults, and old individuals.

When a flood comes, young, sick, disabled, and elderly insects and rats will die in the flood because of their poor mobility and ability to escape. Relatively speaking, strong adult insects and rats have a much greater chance of escape.

Therefore, generally speaking, after a flood, the number of local insects and rats actually decreases, but since the dead are the old, weak, sick and disabled, the survivors are the stronger adults. At this time, the food and resources originally allocated to the old, weak, sick and disabled will be divided up by the surviving adults.

Because the adult individuals have strong reproductive capacity and vitality, and because food and living space are more abundant after the flood than before the flood, these adult individuals will reproduce in large numbers in a short period of time.

Wet Mouse

(Photo source: Veer Gallery)

The life cycle of insects and rats is short, so their population will increase rapidly in a short period of time, even far exceeding the number of insects and rats before the flood. And compared with the population before the flood, the population of insects and rats after the flood is almost entirely made up of young and middle-aged individuals, while the elderly and sick individuals are almost gone.

This also explains why there are more insects and rats after the flood. On the one hand, it is because the surviving young and middle-aged individuals reproduce their offspring in a short period of time, causing the population to increase. On the other hand, the proportion of young and middle-aged individuals in the insect and rodent population has greatly increased, making the insect and rodent population more energetic, which can also give people the illusion that the number of insects and rodents has increased dramatically.

Humid environment breeds pathogens

It is also because there are a large number of dead and injured animals in the flood, and their bodies are soaked and rotten by water. These rotten bodies, together with the increased surface water and silt after the flood, as well as the damp and dirty environmental factors, all create excellent conditions for the growth of bacteria and viruses. Therefore, the number of pathogens of infectious diseases will increase after the flood. At the same time, with the large increase in insects and rats, which are infectious media, and the pollution of the water body itself after the flood, the spread of infectious diseases has also greatly increased, causing the local people who have experienced the heavy damage of the flood to suffer secondary disasters again. For example, in the Yangtze River flood in 1931, after the flood washed away 186 counties and cities and affected 8.38 million mu of farmland, typhoid and dysentery broke out.

Flooded house

(Photo source: Veer Gallery)

Conclusion

Although floods are natural phenomena caused by rapid rise in water levels due to natural factors such as heavy rains and storms, scientific research records show that human activities such as deforestation and land expansion are also significantly correlated with the frequency of floods.

Returning farmland to forests and planting trees should not be just a slogan, but should become part of the daily actions of every one of us on earth.

In fact, we can help protect forests and resist floods through some small things in our daily lives. For example, we should try to reduce the use of disposable chopsticks, follow the rules and avoid open flames in the mountains and forests, protect the environment and reduce pollution, and actively plant trees. The awareness of caring for forests should be engraved in our hearts and should also be reflected in every little thing in life. Let us start from now on to protect the forests and our beautiful home.

Planting trees

(Photo source: Veer Gallery)

Editor: Ying Yike