International Business Department           Liu Bojia           May 27, 2023

  As summer arrives and temperatures rise, that dreaded household creature, the cockroach, is coming back. It may come out of nowhere from all kinds of dark corners and make your hair stand on end. Due to the difference in geography, the main cockroach species in southern and northern China differ. Cockroaches in the south are usually the American cockroach, which are larger and can fly briefly, but due to their weak flight control, they may run across people's faces.

  Northern cockroaches are smaller and dominated by the German cockroach, which prefers to live in colonies in piles of debris, heating ducts, or crevices in furniture. A recent study in the Proceedings of the National Academy of Sciences of the United States of America analysed the history of the German cockroach's origins and showed that the German cockroach did not come from Germany, but more likely originated in South Asia and spread globally in response to human activity.

  The cockroach Blattella germanica was first described in Europe by Swedish biologist Carl Linnaeus back in the 18th century, and was given the nickname German cockroach because samples were collected in Germany.

  Although today the German cockroach can be found in most parts of the world, with the exception of Antarctica. However, when it was first described by the scientific community, the German cockroach bore so little resemblance to other cockroaches native to Europe that scientists have long suspected that the German cockroach is not native to Germany, but where it is from has remained a mystery.

  For the past decade, a team of researchers at Harvard University's Theodore Evans has been trying to solve the mystery of the German cockroach's origins, initially using small fragments of DNA to compare German cockroaches from different regions, but this information was still insufficient. With the development of whole genome sequencing technology, they have more genetic information to analyse.

  In the new study, the team collected samples of German cockroaches from all continents, and by comparing the similarities and differences in their genomes, they were able to work out when and where the German cockroaches from different regions were passed on.

  Based on the comparison of genetic information, they found that a closer relation to the German cockroach is Blattella asahinai, a cockroach that lives in South Asia, from which the German cockroach may have separated about 2,100 years ago and adapted to consume human food.

  And based on the genomic differences between German cockroaches from different continents, they surmised that the German cockroach spread around the world through two migratory currents. The first occurred about 1,200 years ago, when they travelled out of South Asia with the trade caravans travelling to and from the Middle East, and settled in the Middle East by crossing the natural barrier of the desert.

  The second spread, on the other hand, occurred about 390 years ago, when colonialism was on the rise and the German cockroach began travelling with merchant ships from South and Southeast Asia to the European region, especially as improved heating systems provided by ships allowed the German cockroach to survive the sea voyage and reach the European landmass.

  The researchers note that these findings link the genetic data of the German cockroach to historical events for the first time, which helps to provide a truer picture of how they spread. Of course, in addition to humans providing a tailwind that facilitated the spread, the German cockroach's own extreme adaptability was key to their ability to take over the globe, and these two conditions were the perfect combination of elements to allow the species to succeed in the human world.