Genetics reveals the surprising origin of the German cockroach

The German cockroach lurks in human homes, cities, and structures worldwide. You won’t find it crawling through natural habitats – it’s entirely domesticated.

The pest species, Blattella germanica, was first recorded in central Europe about 250 years ago. But its origin and spread has remained a mystery until now.

But a team of researchers has now confirmed the species evolved from the Asian cockroach Blattella asahinai about 2,100 years ago and probably did this by adapting to human settlements in India or Myanmar.

“We found that the sequence for the German cockroach was almost identical to that of B. asahinai, a species native to the Bay of Bengal, from east India to Bangladesh and into Myanmar,” says Theo Evans of the University of Western Australia, who co-authored the study published in Proceedings of the National Academy of Sciences.

Genomic analysis of DNA collected from 281 cockroaches, from 17 countries across 6 continents, revealed 2 routes through which the species spread across the globe.

“We found an early spread route around 1,200 years ago, which was from eastern India westwards, likely from increasing trade and military activities of the Islamic Umayyad or Abbasid Caliphates,” says Evans.

“The next spread route was eastwards around 390 years ago into the Indonesia archipelago, likely facilitated by various European East India Companies. These companies traded spices, tea, cotton and other products within South and Southeast Asia, and back to Europe.

“We estimated that German cockroaches arrived in Europe about 270 years ago, which matches the historical records from the Seven Years’ War. From Europe the German cockroach spread to the rest of the world, around 120 years ago, probably from faster transportation on steam ships.”

B. germanica grows to about 1.1-1.6 centimetres long and varies in colouration from tan to almost black. They are omnivorous scavengers attracted to meats, starches, sugars and fatty foods.

“To survive, cockroaches have to avoid being seen by humans. German cockroaches have evolved to be nocturnal, avoid open spaces, and although it retained its wings it has stopped flying,” says Evans.

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