Ahhhh help! The southern cockroaches have really invaded the north! What should I do? !

Recently, many friends in the north have encountered an unprecedented severe "survival crisis" -

It’s not the summer temperatures that are approaching 40°C, but the giant cockroaches that originally lived in the south have moved to the north! (Congratulations! People in the north can now grab the whole summer like people in the south, which is really a cause for celebration~)

Image source: Weibo screenshot

What is behind all this? Is it the decline of morality, the distortion of human nature, or global warming?

To explore this issue, we need to answer three questions:

Are southern cockroaches southern cockroaches?

Is the northern cockroach the northern cockroach?

Why did southern cockroaches begin to move north?

01

Is the “Southern Cockroach” a Southern Cockroach?

The order Blattodea, to which cockroaches belong, is a typical tropical-subtropical animal group. The warm climate in the south close to the equator (the north for areas in the southern hemisphere, we are mainly discussing the domestic situation here) is their happy home.

Southern my country, especially the tropical and subtropical regions such as Yunnan, Guizhou and Guangdong, has a unique natural environment of warm and humid, rich biodiversity, and cockroaches are no exception.

The native cockroaches in the south are very colorful. There are giant light cockroaches , true cockroaches that shine with beautiful metallic luster and like to visit flowers , bent-wing cockroaches that live in rotten wood , ball cockroaches that can roll into a ball like ball-headed woodlice , and even groups of specialized insects that are ant-dwelling.

The dwarf cockroach curls up into a ball when frightened. Image source: @吴士玮

They are part of my country's biodiversity and are important decomposers in nature. Not only are they not close to humans, but they are victims of human invasion of nature. Many unique species with narrow distribution and high environmental requirements (especially cave species) may have become extinct before they were discovered and described by the scientific community.

As for the "Southern cockroaches" mentioned on the Internet, they are basically the American cockroach, Australian cockroach and black-breasted cockroach. These are large cockroaches that like to hang around humans , sometimes break into homes, and have a strong visual impact.

They have long been spread all over the world with human activities, and it is difficult to verify their original distribution range; but it is generally believed that American cockroaches and Australian cockroaches come from Africa, while black-breasted cockroaches are native to Asia. So the former two are alien species, while black-breasted cockroaches may indeed be native to southern China.

American cockroach. This image is copyrighted by the image library. Reproduction or use may cause copyright disputes.

02

Is the “northern cockroach” a northern cockroach?

As mentioned earlier, most Blattodea species are distributed in warm areas; however, there are also a few hard-core cockroaches that can survive the cold winters in the north and have made the north their home for generations.

For example, the Chinese true ground beetle is a northern cockroach native to China . The male has wings and can fly, and is quite large, which actually fits the impression of northern netizens on southern cockroaches. The females and nymphs are both round ground-dwelling insects, playing in the mud in the northeast for generations. However, like most cockroaches, they do not like human residences, but live a simple life in the wild, facing the loess and back to the sky.

Chinese softshell turtle. Image source: Zhihui Sannong

For modern people who are accustomed to city life, these northern cockroaches that have lived here for generations are very unfamiliar. The real owner of the title of "northern cockroach" on the Internet is another cockroach - the German cockroach .

German cockroach. This image is copyrighted by the image library. Reproduction or use may cause copyright disputes.

Their origin is not particularly clear, and it is generally believed that they originated from Southeast Asia and are authentic southern cockroaches. They are distributed together with a group of relatives represented by the Asian cockroach, which look almost exactly like the German cockroach, but only live in the wild and have very different habits. Some of them are even beneficial insects for agriculture and forestry with certain predatory properties.

The German cockroach is an outlier in the entire cockroach family, and is a cockroach that has fully adapted to the human environment . Although the main members of the "Southern Cockroach", the American cockroach, the Australian cockroach, and the black-breasted cockroach, occasionally appear in human homes, and even lay the foundation for the stereotype of the thousands of species of the entire cockroach family, they are not fully adapted to the human environment and do not like to live indoors.

Their main activity areas are outdoors around human residences, such as debris piles and garbage dumps in front of and behind houses, sewers, greenhouses, and farms. The big and small cockroaches you encounter at home actually spend most of their time outdoors, only sometimes visiting the house.

The German cockroach is different. They are highly adapted to the human environment and will live indoors all their lives and reproduce. They have spread all over the world with the footsteps of humans, not only in the north but also in the south. The only place they have not conquered is Antarctica.

Calling it the northern cockroach is a bit narrow-minded, as it is the world's cockroach.

In addition, there are several larger cockroaches that appear around humans: the Oriental cockroach from the Black Sea-Caspian Sea area and the Japanese cockroach from Japan.

These two are not the delicate cockroaches that grew up in a greenhouse. They have a strong tolerance to cold and can live in both the north and south. However, they are relatively less common and have a lower presence. Their habits are similar to those of the American cockroach, which can also live around humans, but prefer to keep a social distance.

03

Why do cockroaches from the south migrate north?

Now we have the answer to why cockroaches from the south moved north.

Although most species of cockroaches like to live in nature in warm and humid areas and try to avoid humans, there are a few heretics in the cockroach family who actually want to make a living from the terrifying upright apes.

Their bold decision to go against their ancestors paid off - they followed humans and continued to expand into new territories . The German cockroach, which has the strongest business capabilities and is truly fully adapted to the human indoor environment, started from Southeast Asia and conquered the world (houses); when northerners who don't have many insects in their homes saw them, they thought they were specialties from their hometown.

The American cockroach, Australian cockroach and black-breasted cockroach are the second tier, among which the American cockroach is the most adaptable and the most common. Although they are also used to picking up some leftovers from us, it is difficult for them to accept living under the same roof with humans. Most of the time, they choose to settle in sewers and garbage dumps around human residences. This makes their living conditions in winter far worse than those of German cockroaches, and the cold winter hinders their steps to the north.

Visual monitoring of cockroaches in different provinces in 2019. Image source: Yue Yujuan, Ren Dongsheng, Wu Haixia, Liu Xiaobo, Zhao Ning, Guo Yuhong, Li Guichang, Wang Xueshuang, Song Xiuping, Wang Jun, Lu Liang, Liu Qiyong. National cockroach monitoring report in 2019. Chinese Journal of Vector Biology and Control, 2020, 31(4): 412-416.

I grew up in a rainy season area, when the Internet was not well developed or even existed. To me, the so-called "Southern cockroaches" now were what the cockroaches I saw at home should look like.

Later, I came to the United States to live in the New Jersey-New York area, which is equivalent to the latitude of Beijing, and conducted field surveys on urban pests. American cockroaches are still a very common cockroach species. They live outside houses in warm seasons; many materials generally say that American cockroaches will enter indoors to hibernate, but there is a lack of detailed research on the exact hibernation location.

I have participated in surveys of many locations, different types, and a large number of houses. Even in winter, the sticky insect boards collected indoors were all German cockroaches, and almost no American cockroaches. Therefore, based on my personal experience and opinion, American cockroaches may also tend to choose microhabitats with little human activity and high humidity in winter, such as basements, laundry rooms, garden composts and firewood piles, which are common configurations of American houses .

Copyright images in the gallery. Reprinting and using them may lead to copyright disputes.

The large sewer space in the United States also provides an ideal habitat for them. Although I have no say in the situation in northern China, by analogy, as long as the problem of overwintering places is solved, "southern cockroaches" can definitely drift north .

As China's infrastructure continues to develop, the number of microhabitats suitable for cockroaches to overwinter is likely to continue to increase. As logistics and human traffic move north in the summer, southern cockroaches can also set up camp here and make it their home for generations .

Now we have answers to these three questions:

China's native southern cockroaches have a very high diversity, ranging from large to small, flying in the sky, swimming in the water, burrowing in wood, and burying in the soil. The "southern cockroaches" mentioned on the Internet are mostly the invasive American cockroaches and Australian cockroaches. Although the cockroach species in the north are far less abundant than those in the south, there are also large northern cockroaches. The "northern cockroaches" mentioned on the Internet - German cockroaches, are neither northern nor German, but southern cockroaches, and they are also found in the south . "Southern cockroaches transferred to the north" has never been uncommon. The northern cockroaches mentioned on the Internet now are actually the first batch of southern cockroaches that successfully immigrated with their hard power. With the increasing development of logistics and heating, there are more and more small environments in the north that are suitable for cockroaches to spend the winter , and the larger southern cockroaches have also begun to become permanent residents in the north.

Unlike the German cockroach, which is very tolerant to dryness, the American cockroach is more dependent on water and a humid environment .

Indoors in the south are also very humid, so they still visit frequently; in comparison, the dry indoors in the north are very scary to them. For the sake of their sensitive skin, "southern cockroaches" will probably stay away from northern homes.

In any case, it can be regarded as a little comfort to our friends in the north, apart from the unexpected negative effects brought about by the improvement of logistics and living conditions.

Author:ChenZ

Reviewer: Yin Haisheng, Senior Engineer, Researcher-level, Shanghai Insect Museum, Chinese Academy of Sciences

Planning Editor: Xu Lai

Editor in charge: Yang