Cockroach: How a reviled pest from India colonised the world

A new study deciphers the historical routes that the most common species of cockroach took from its origins in Asia. 

Published : May 21, 2024 13:34 IST - 4 MINS READ

Scientist studied DNA samples of 281 German cockroaches from 17 countries, across all six human-inhabited continents.

Scientist studied DNA samples of 281 German cockroaches from 17 countries, across all six human-inhabited continents. | Photo Credit: Betka82

The stuff of nightmares, the grotesque protagonist of Franz Kafka’s 1915 novel The Metamorphosis, the primary target of the contemporary world’s costly battle towards pest control—the cockroach—is the subject of a new scientific paper that traces its origins to India, from where it went on to colonise every continent except Antarctica.

A large group of scientists, in a research paper in the latest Proceedings of the National Academy of Sciences (PNAS), studied DNA samples of 281 German cockroaches (Blattella germanica)—the most prevalent cockroach species—from 17 countries, across all six human-inhabited continents. And they found the creatures were not quite German after all. The authors concluded that the species “evolved from the Asian cockroach Blattella asahinai approximately 2,100 ya [years ago], probably by adapting to human settlements in India or Myanmar.”

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So how, and when, did the insect go from its Asian home to become the most ubiquitous urban pest? Genomic analyses found two routes: the first a route to West Asia, some 1,200 years ago, “coinciding with various Islamic dynasties”, and the second route, around 390 years ago, “coinciding with the European colonial period,” likely aided by the Dutch and British East India Companies, says the paper. The German cockroach, despite its name, did not appear in Europe until around 270 years ago.

Advances in transportation such as steam engines, the globalisation of trade, houses with plumbing and heating, each facilitated the roach’s colonisation of the rest of the world between the late 19th and early 20th centuries. Outside Europe, the first occurrence of the species was in New York, in 1842, during the construction of the Croton Aqueduct. “New Yorkers believed that the aqueduct brought the pest to the city, and so-called German cockroaches the Croton bugs,” Qian Tang (the lead author of PNAS paper, and now a research associate in evolutionary biology, Harvard University) et al wrote in the journal Biological Invasions, in 2018.

Name calling

During their research, “The spotlight fell on the star of our story in eastern Europe when [the cockroach] was spotted in army food stores during the Seven Years’ War (1756–63). Each of the opposing forces named the cockroach after the other – the Russians called it the ‘Prussian cockroach’, while British and Prussian soldiers called it the ‘Russian cockroach’,” write co-authors of the PNAS paper, Theo Evans (associate professor of applied entomology, The University of Western Australia) and Tang, in The Conversation.

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It was not until 1767 that the Swedish biologist Carl Linnaeus named the species Blatta germanicaBlatta, in Latin, means “avoids the light”. And it got the tag ‘germanica’, only because the specimens he examined happened to be collected in Germany, the article explains.

Tang and his co-authors delve into the etymology in Biological Invasions. In English, the word ‘cacarootch’ was first introduced in 1624, in a letter written in Virginia by a captain, John Smith, who described the insect thus: “a certaine India bug, called by the Spaniards a cacarootch, the which creeping into chests they eat and defile with their ill-scented dung.” The name ‘cockroach’ became “widely accepted when Charles Darwin settled it in 1859,” says the paper. Darwin indeed references the ‘small Asiatic cockroach’ in his 1859 classic On the Origin of Species.

A China story

Today, the cockroach “imposes significant social, medical, and economic costs due to prevalent insecticide resistance allowing it to outcompete [with around] 40 known pest cockroach species in buildings,” the authors note in PNAS. A study conducted in China, published this January in Nature Scientific Reports, concluded that “Cockroaches can harbour and spread many foodborne microbial pathogens, including bacteria, viruses and parasites, which means that cockroaches may play a wide range of roles in the spread of foodborne infections.” The pathogens detected in cockroaches included sapovirus and E. coli. Troublingly, the study found that food service areas in schools were more conducive to the breeding of cockroaches.

The scientists discuss the nocturnal insect’s ability to biologically shape-shift to quickly evolve resistance to insecticides. In fact, resistance can appear within a few years, we learn, making it difficult to find new active ingredients, “given the high cost of discovery, safety tests and registration,” they write in The Conversation. The article ends ominously: “… the German cockroach will continue to evolve and adapt to stay alive, so the arms race between us and the cockroach will go on for years to come.”

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