When people started moving freely around the globe, they also began relocating the world’s flora and fauna. To what extent is open to speculation – as are the consequences.

We are redistributing our world. More and more frequently, we humans are determining the habitats of plant and animal species. It’s unavoidable as we navigate ships across the oceans, jet back and forth between continents, build canals and bridges, forget to lock our pets’ cages at night, import exotic flowers for our gardens, and return from vacation with souvenirs hosting tiny pathogens. As a result, the world’s largest herd of wild camels now lives in Australia, not in northern Africa. South American prickly pears are growing in Spain. North American raccoons are nesting in German attics. And Australian eucalyptus trees are more widespread in Portugal than the country’s native tree species.

Plants introduced into alien areas by human hand are called neophytes, their animal counterparts neozoa. Together they are known as neobiota – a term composed of the ancient Greek words néos (new) and bios (life). The unprecedented enthusiasm with which we humans are scattering neobiota across our planet is shifting the boundaries between the natural, ancestral habitats of our flora and fauna. To what extent, however, is largely unknown. In 2015, the Dutch biologist Mark van Kleunen produced the first-ever headcount of globally distributed neophytes, publishing his total of 13,168 in the esteemed scientific journal “Nature”. This is roughly equivalent to the sum total of Europe’s native flora species. There is no comparable coverage of alien species in the animal kingdom, partly because the levels of documentation differ from country to country. Experts are currently compiling a global database, but even amateur naturalists can help with the collation. For example, the European Commission is asking EU citizens to report non-native flora and fauna using the specially-developed Invasive Alien Species Europe app. In Germany, for example, the Federal Office of Nature Conservation has listed 319 non-native animal species and 566 plant species that have become established in the country. Additionally, there are some 450 animal and 1,650 plant species that have been spotted occasionally but are yet to form permanent colonies. How exactly they reached their new homes varies greatly from species to species, says Jonathan Jeschke, an ecologist and researcher at the Free University of Berlin and Leibniz Institute of Freshwater Ecology and Inland Fisheries. “You can divide the newcomers between intentional and unintentional imports,” he says, “with the intentionally transported species further subdivided into released and escaped categories.” By way of illustration, the Asian long-horned beetle entered Germany as a well-hidden stowaway in wood destined for construction and packaging. It was inadvertently introduced and then escaped. The African clawed frog, on the other hand, was deliberately imported – for research in a Portuguese laboratory. When heavy rain caused a local river to overflow, the institute was flooded and the frogs escaped – multiplying unnoticed for years in the Greater Lisbon area. And the gray squirrel was intentionally released in countries like Italy and England, after which it proliferated exponentially.

“Vertebrates and plants tend to be imported on purpose, invertebrates and pathogens accidentally,” observes Jonathan Jeschke. The year 1492, when Christopher Columbus landed in America, is thought of as the zero hour for neobiota. “From that point onwards, humans progressively dismantled the barriers hindering the spread of animals and plants,” explains Jeschke. In the nineteenth century, European settlers smuggled species en masse into their new homes, and since the turn of the twentieth century, world trade has been moving ever-larger quantities of plants and animals around the globe – with the numbers still rising annually. Uninvited guests have even been discovered in Antarctica, having completed the voyage by chance on the soles of hiking boots or the Velcro fasters on jackets.

The consequences are manifold. What do the Asian long-horned beetle, African clawed frog and gray squirrel have in common? They are all considered invasive, species characterized by the International Union for Conservation of Nature (IUCN) as proving disruptive in their new homelands. The beetle chews pits in the bark of deciduous trees, from which its larvae tunnel deep into the trunks; in this way it can destroy entire forests. The frog devours all inferior amphibians within its range, pushing native species to the brink of extinction. And the gray squirrel transmits a virus. While the host animals are immune to its effects, it can be fatal to the indigenous red squirrels of central Europe.

According to the IUCN, invasive species are the main causes of extinction among the amphibians, reptiles and mammals enumerated in its directory of flora and fauna at risk: the Red List. The economic damage they cause has been estimated at hundreds of billions of euros a year. In order to assess which invasive species to target, Jonathan Jeschke and other scientists are currently creating a database for the IUCN that classifies the threat level of each species.

However, establishing what is harmful can prove challenging. “Harm is just a perspective,” says Mark Davis, an American plant ecologist and author of the book “Invasion Biology”. What many conservationists regard as ecological harm is actually just a preference for native species, he argues. He rejects the assumption that home-grown automatically means good and non-native automatically bad – a stance supported by a study showing that large alien herbivores such as wild horses can benefit and enrich ecosystems through their grazing. Moreover, the opportunity to flourish in new environments often helps preserve species completely – like the above-mentioned camels in Australia, which are being increasingly displaced in their original homeland. If new breeds do not cause significant damage, Mark Davis promotes the almost romantic approach he calls “LTL” – the abbreviation for “Learn to Love ’Em.” And that is definitely easier with some species than with others.


Svenja Beller freelances for a range of magazines and newspapers. She lives and works in Hamburg and Lisbon.