The cockroach that lives rent-free in your sink drain and stores its food under your fridge is likely a pest called the ‘German cockroach’, and its ancestors were troubling people more than 2,000 years ago in southern Asia, according to a new study.
The research, published on May 20 in the journal Proceedings of the National Academy of Sciences, revealed that the insects’ progression from scavenging in ancient Asian civilizations to hiding beneath modern kitchen floors aligns closely with significant historical shifts in global commerce, colonization, and war.
German cockroaches, scientifically named Blattella germanica, are common in cities across the United States and worldwide. They first appeared in scientific records in Europe 250 years ago, hence their German name, but their origins were largely unknown.
To uncover the spread of these cockroaches, lead study author Dr. Qian Tang and his team asked scientists and pest control experts worldwide for local specimens. The team received 281 German cockroach samples from 57 locations in 17 countries and analyzed their DNA to trace their evolution.
“Our main goal was to show how a species can travel with humans and how genetics can fill in gaps in historical records,” said Tang, an evolutionary biologist now a postdoctoral research associate at Harvard University.
Modern cockroach’s lineage dates back much further than 18th-century Europe
Using genomic data from the samples, Tang discovered that the modern cockroach’s lineage dates back much further than 18th-century Europe. The insect evolved from the wild Asian cockroach, known as Blattella asahinai, 2,100 years ago, according to his research.
Around that period, Tang and his colleagues theorized, people in what is now India or Myanmar started farming in the Asian roach’s natural environment. The insects adapted, shifting their diet to human food, and eventually moved into human homes.
A thousand years later, as trade and military activities expanded between southern Asia and the Middle East, and later Europe, domesticated cockroaches spread westward, likely traveling in soldiers’ and travelers’ food supplies.
The genetic analysis by the study team suggests the insects first entered Europe around 270 years ago, which aligns with when Swedish geneticist Carl Linnaeus first described them in 1776, about a decade after the Seven Years’ War spanned Asia, Europe, and North America. The cockroaches then reached the Americas roughly 120 years ago, the study indicates.
“Insects are part of the fabric of human culture,” said Dr. Jessica Ware, curator of invertebrate zoology at the American Museum of Natural History in New York City, who was not involved in the research. “For the longest time, we’ve kind of known that people are moving around a lot of pest species. And we know that transatlantic trade routes probably were the culprit for the spread of German cockroaches. But to actually see this reflected in the genetic signature of these populations, that was very exciting.”
Humans have been accommodating them ever since she noted. “The things that have allowed humans to thrive — indoor plumbing, indoor heating — are things that have also allowed cockroaches to thrive,” Ware said. “By creating sewers underneath our cities, we couldn’t have provided a better buffet.”
Tang’s next goal is to sequence the full genomes of his numerous specimens to understand how German cockroaches have adapted so well to human environments. “For example, the German cockroach has insecticide resistance that is not detected in many other pests,” he said. “How can they evolve so fast? Is it something that’s already in their genes, but has become revealed because of anthropogenic pressures?”
The insects also show social behaviors, such as communicating with each other for food sources. Tang wants to determine if this ability is another survival trait influenced by humans.
