Most cockroaches don’t bother us. They have been existing in the various ecosystems of the Earth 130 million years, helping to recycle the organic matter they feed on. Today, there are approximately 4,000 species and less than 1% live among us. Among them, only one, the German cockroach (Germanic Blattella), is what causes most of the plagues in the world. At last, science has traced its history.
It turns out that the German cockroach lives exclusively in urban environments, there is no population in the wild. So where do they come from? Despite its name, it has never been believed that it came from Europe, since here we do not have other species of the genus Blattella.
The first historical record of this animal in Europe dates back to the time of the Seven Years’ War (1756-1763). The common names they gave They varied depending on the side: The Russians called it the “Prussian cockroach” and their opponents the “Russian cockroach.” Finally, in 1767 Linnaeus collected some specimens in Germany and named it Germanic Blattellabut I really didn’t know its origin.
It was believed that this cockroach could come from Africa, until in 1950, scientists from Harvard University made an expedition to India and discovered another strikingly similar cockroach. The hypothesis that it came out of Asia became the most accepted, but how it spread throughout the world remained a mystery. Until now.
A group of scientists have taken DNA samples from these arthropods in 17 countries around the world and compared their sequences. The results, recently published in the journal PNAShave allowed them to trace the journey of the German cockroach from its origin to our homes.
The German cockroach sequence was almost identical to that of the Blattella asahinai, a cockroach from the Bay of Bengal. This means that these two species diverged relatively recently, specifically 2,100 years ago, probably when Indian farmers left the countryside to live in cities.
It first left India 1,200 years ago and headed west, but it didn’t get very far. Later there was another wave that reached Indonesia and only 270 years ago, they reached Europe, which agrees with accounts of the Seven Years War. Finally, they colonized the rest of the world 120 years ago.
The fact that the German cockroach began to travel so recently has an explanation. This species is characterized by having a very short life expectancy, which implies that, to distribute throughout the world, it needs short transport times. As human technology progressed, transportation became faster and travel times became shorter. It is therefore not surprising that the greatest expansion of cockroach distribution occurred in the 20th century.
This is explained by the authors of the study in The conversationn: “We believe that global trade facilitated this expansion, because the most closely related populations are found in countries with cultural ties, rather than in countries that are simply close to each other.”
Furthermore, the German cockroach is a tropical species that has an optimal temperature of between 25 and 32ºC. As human technology improved the interior conditions of homes, such as heating and insulation of buildings, this animal was able to expand its range to temperate zones. The heat from the mechanical and electrical motors of elevators, escalators or generators also helped.
It is striking that, being the two species of cockroaches so similar, one has stayed in the fields of India and the other has become totally urban to follow humans around the planet. What aspects of an animal can trigger such a change in lifestyle?
High reproduction rate and more gregarious
In addition to having a short life, the German cockroach is characterized by having a smaller size, which allows maintaining a larger population when resources are limited. This translates into more cockroaches in less time, which increases the rate of evolution and therefore the ability to adapt. German cockroaches could quickly adapt to new environmental circumstances, such as new building materials, new types of food, and other human factors. And also easily develop resistance to insecticides.
But the main difference between the German cockroach and the Asian one is that the German is gregarious, allowing more individuals to survive in small shelters within human habitations. This is very important. If we think about it, most of the animal species that form pests in cities are characterized by being very social, like rats.
This species shows the most advanced social organization among all cockroach species that can be considered a pest. When isolated outside their group, German cockroaches suffer from “isolation syndrome”. Symptoms include delayed sexual maturation and various behavioral disorders, such as less foraging and less demandingness when evaluating potential breeding partners.
Furthermore, when they are isolated they reduce the amount of hydrocarbons they express in their cuticle. These molecules are responsible for regulating their social behavior, are what allow them to recognize each other among related cockroaches and decide who they hang out with. In contrast, other species of cockroaches do not show these symptoms.
Therefore, we have a species of cockroach that, due to its high reproduction rate and gregarious behavior, has managed to adapt perfectly to life in the city. The comfort we create in our homes is also their comfort and, at the moment, there is no insecticide capable of killing an animal that adapts so easily. Most likely, as long as there are humans on Earth, the German cockroach will remain with us.
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