They are not just the usual travel “companions” of today and of those who live indifferently in city areas or in the countryside: the Beatles (also called cockroaches) have existed for more than two thousand years and have spread widely throughout the world well before globalization and travel by plane, ships and other means of transport. From the United States to Australia, from Scandinavia to South Africa, these insects are present everywhere. How is it possible?
The study on travel
To reconstruct their movements, some researchers have tried to solve what is considered a real mystery: in the journal Pnas, where the work carried out by Stanford University is published, they explain that the origin of the German cockroach, Blattella germanica , is partly enigmatic”because it is ubiquitous throughout the world in structures built by man but absent from any natural habitat”. Even if the first testimonies claim it was already present 250 years ago in Central Europe, its ancestors populated the world well before with the Blattella germanica which “it evolved from the Asian cockroach Blattella asahinai about 2,100 years ago“.
The search results
To understand how cockroaches have traveled thousands and thousands of kilometers around the world, the first author of the study and his collaborators examined closely 281 samples of German cockroaches from 57 sites in 17 countries different to study their DNA and understand what the evolution may have been. “Our main aim was to show how a species can travel with humans and how genetics can compensate for the missing part of the historical record“said Qian Tang, an evolutionary biologist, research associate at Harvard University and first author of the study.
The data highlighted that this cockroach, which already existed over two thousand years ago, spread from India and Myanmar thanks to trade and military activity between South Asia, the Middle East and Europe, spreading increasingly towards the west. But how? Simple, they traveled in the baskets soldiers' dining rooms, traders' dining rooms and who knows what other “improvised means of transport” into which they slipped and then exited thousands of kilometers away.
Little by little, with these methods, the diffusion was more and more widespread until the first ones were found European traces about 270 years ago as the expert Swedish geneticist Carl Linnaeus described for the first time in 1776. The study then found that cockroaches spread to North and South America about 120 years ago.
The role of transatlantic trade
“Insects are part of the fabric of human culture“he told the CNN 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. “We have known for a long time that people move around many species of parasites. And we know that trade routes transatlantic probably were the responsible from the diffusion of the German cockroaches. But to actually see this reflected in the genetic signature of these populations was very exciting.”.
As the centuries passed, their unwanted presence also appeared in homes. How did they manage to proliferate even inside homes? “The things that allowed humans to thrive – plants plumbers interior, heating internal – are things that have also allowed cockroaches to thrive” Ware emphasized. “By creating sewers under our cities, we couldn't have provided a better buffet.”
The incredible thing, still under study, is the perfect adaptation of the German cockroach to the habitat of the human being with a strong resistance to insecticides”which is not detected in many other parasites“, the researchers point out.