A New Study Traces the Evolutionary Journey of the German Cockroach Throughout Human History from Islamic Empires to Modern Europe.
Despite its name, the German cockroach (Blattella germanica) is now found on every continent except Antarctica. In fact, scientists regard it as the most common species among the 4,600 cockroach species on Earth. Essentially, they were unknown in Europe until Swedish biologist Carl Linnaeus first described them in 1767. They have no close relatives there and do not exist in the wild. The reason they have become a global pest lies in the DNA of the German cockroach, according to a study published on January 20 in the journal Proceedings of the National Academy of Sciences.
The German cockroach spreads worldwide due to its adaptability and rapid reproduction. (Photo: Action Pest Control).
Through analysis of the complete genetic markers of 281 cockroaches from 17 countries across 6 continents and measuring their genetic closeness, scientists have traced the rapid increase and expansion of the German cockroach for the first time. All signs indicate that they evolved from the Asian cockroach (Blattella asahinai) approximately 2,100 years ago in present-day India and Myanmar. By abandoning their natural habitat to live under human influence, the German cockroach seems to have made its way to the Middle East about 1,200 years ago, possibly due to increased trade activity and military campaigns during the Islamic Umayyad or Abbasid dynasties, which extended from North Africa to Western Asia.
The German cockroach experienced another geographic leap around 390 years ago as colonization activities increased, bringing them to Europe and subsequently the rest of the world thanks to improvements in transportation, trade routes, and indoor heating systems that allowed this insect to survive in cold weather. Clearly, every migration and movement of the German cockroach has been facilitated by humans. “The German cockroach can’t even fly,” said Qian Tang, an evolutionary biologist at Harvard University and the lead researcher. “They hitch rides on human vessels around the globe.”
However, the successful spread of the German cockroach is not merely due to luck. Instead, the main reason lies in their adaptability and evolutionary traits. This is something that scientists today are still striving to understand.
To illustrate how much the German cockroach has changed over two millennia, the research team compared it with its closest living relative, the Asian cockroach. Although the two species are nearly identical, they exhibit very different behaviors. The Asian cockroach flies towards light sources, while the German cockroach hurriedly scurries away, according to Chow-Yang Lee, an urban entomologist at the University of California, Riverside. Similarly, if you were to throw both species into the air, the Asian cockroach would fly, whereas the German cockroach would land on the ground and run away.
The study also revealed that the genome of the German cockroach reflects its relationship with humans. For example, German cockroaches in Singapore and Australia are more closely related to those in the United States than to the population in Indonesia, likely due to the higher level of trade activity between the U.S. and Singapore and Australia compared to Indonesia.
The German cockroach also outcompetes other cockroach species wherever it appears, according to Tang. One reason for their success is their faster reproduction rate compared to most other cockroach species, allowing them to quickly develop resistance to insecticides. Previous studies revealed that after years of baiting cockroaches with poison-laced sugar, the surviving population produced a new generation that no longer ate sweet substances.
