DNA Reveals How German Cockroaches Came to Dominate the World

The German cockroach lives not in the wild, but in human buildings across the globe. The widespread species is the world’s most prevalent cockroach, but scientists have been unsure where it originally came from.

In a new study of German cockroach genetics published Monday in the journal Proceedings of the National Academy of Sciences, researchers map the spread of the pest over the last couple millennia. As humans increasingly traveled between continents, cockroaches tagged along.

“The German cockroach can’t even fly,” Qian Tang, lead author of the study and an evolutionary biologist at Harvard University, tells National Geographic’s Jason Bittel. “They hitchhike in human vessels around the world.”

As a result, tracing the history of the prolific pest is “not just an insect story,” as Stephen Richards, who studies insect genes at the Baylor College of Medicine and did not contribute to the findings, tells Adithi Ramakrishnan of the Associated Press (AP). “It’s an insect and humanity story.”

German cockroaches were first recorded in Europe around 250 years ago. Armies in eastern Europe discovered the bugs in their food stores during the Seven Years’ War between 1756 and 1763, the study authors write in the Conversation.

The armies each named the bug after their enemies—Russian soldiers on one side of the conflict called it the “Prussian cockroach,” while the British and Prussian forces dubbed it the “Russian cockroach.” Ultimately, the Swedish biologist Carl Linnaeus named the species Blattella germanica in 1767, after the specimens he happened to collect from Germany.

Historical records have indicated that German cockroaches spread from Europe between the late 19th and 20th centuries. But the species’ closest relatives are in Africa and Asia, not in Europe.

All this historical finger-pointing and conflicting information—along with the cockroach’s lack of natural habitat in the wild—has left scientists at a loss.

“Its origin has been a mystery,” Edward Vargo, a co-author of the study and urban entomologist at Texas A&M University, tells the Washington Post’s Dino Grandoni.

To solve this puzzle of the cockroach’s beginnings, the researchers studied the genes of 281 German cockroaches from 17 different countries. First, they confirmed that the German cockroach evolved from the Asian cockroach Blattella asahinai around 2,100 years ago. This species looks similar to the German cockroach, but it can fly—and it is attracted to light rather than scuttling away from it.

The team suggests that, when humans cleared their natural habitat in India or Myanmar, the cockroaches adapted to live in human settlements, then evolved into a new species.

“We have long suspected that the Asian cockroach is actually the ancestor for the German cockroach, but this paper pretty much nails it,” Chow-Yang Lee, an urban entomologist at the University of California, Riverside, who was not involved with the work, says to National Geographic. “It’s extremely exciting.”

The genomic analyses also indicated German cockroaches spread west to the Middle East around 1,200 years ago. They could travel in soldiers’ bread baskets, and the study authors suggest that commercial and military activities of the Islamic Umayyad or Abbasid Caliphates allowed the bugs to expand their territory. Later, around 390 years ago, the cockroaches spread east, likely due to European colonial commerce between South and Southeast Asia.

It wasn’t until just 270 years ago that the bugs entered Europe, according to the researchers’ estimates, and they spread to the rest of the world in the late 19th and early 20th centuries. This timeline is supported by historical records.

As technological advancements allowed for speedier travel, cockroaches could spread across greater distances with global trade. Then, indoor heating and plumbing enabled their survival in colder areas.

Lee tells the New York Times’ Sofia Quaglia that the work is a “landmark study.”

Further genomic research could help scientists to better understand the cockroaches’ spread and the evolution of their resistance to insecticides, which could, in turn, lead to better pest management.

Cockroach infestations are “a big public health concern, especially in low-income housing where the treatments for German cockroaches leave a lot to be desired,” Vargo tells the Washington Post.

Will Sullivan | | READ MORE

Will Sullivan is a science writer based in Washington, D.C. His work has appeared in Inside Science and NOVA Next.