In 1905, a Bohemian prince released 5 muskrats into his estate. By 1914, their population had exploded to 2 Million

What began as a small private experiment on an estate near Prague turned into one of Europe's most striking examples of an invasive species spreading across a continent.

In 1905, five muskrats were brought from North America to Bohemia. There were just two males and three females.

Within nine years, estimates suggested that around 2 million muskrats were living across Bohemia.


The animals had escaped the confines of the estate, followed waterways into new territory and begun reproducing far beyond the place where they were first introduced.

What happened next became a decades-long ecological and engineering problem.

It started with five animals

The story is generally traced to 1905, when Prince Colloredo-Mannsfeld returned to Bohemia after a hunting trip in North America, commonly described as having taken place in Alaska.

Among the animals brought back were five muskrats.

They were released into ponds at his estate near Dobříš, about 40 kilometres southwest of Prague.

The motivation was apparently practical. Muskrat fur had commercial value, so keeping the animals offered the possibility of establishing a small fur source.

At first, the muskrats were essentially captive animals. They were reportedly fed grain, carrots and other food.

But the ponds were never going to remain their entire world.

Once some animals escaped, they encountered an environment particularly well suited to their biology.

Rivers became their highways

Muskrats are semi-aquatic rodents that spend much of their lives around ponds, streams, rivers, canals and wetlands.

They are capable swimmers and excavate burrows into riverbanks. They also construct nests or lodges among vegetation.

More importantly, established populations produce young that can disperse into neighbouring areas.

That combination created a powerful expansion mechanism.

A muskrat did not need to cross dozens of kilometres of unfamiliar countryside. It could simply move along suitable waterways, establish itself, reproduce and allow the next generation to move farther.

The landscape itself provided a network of routes.

And the numbers began to climb.

From five muskrats to millions

By 1914, historical estimates placed the muskrat population in Bohemia at roughly 2 million animals.

That means the original introduction had gone from a handful of individuals to an enormous established population in less than a decade.

The expansion did not happen as one dramatic invasion wave.

Instead, the population gradually pushed outward.

Historical records later allowed scientists to reconstruct the changing boundary of the species' range. During the early stages, the advancing front was estimated at roughly 10 kilometres per year, although the rate varied considerably depending on local geography.

Rivers could accelerate the process.

Suitable wetlands could become stepping stones.

And every newly established population created another starting point for dispersal.

This was biological expansion operating on a landscape scale.

Europe unintentionally built a muskrat network

Once the species became established in Bohemia, neighbouring parts of Central Europe became accessible.

Muskrats spread into areas of Germany, Austria and Switzerland, while separate introductions and escapes helped establish populations elsewhere, including France and Belgium.

Then humans accelerated the process again.

Muskrats were valuable for their fur, and they were deliberately introduced into new regions for commercial production.

During the 1920s, they were introduced into Finland. From 1928 onward, much larger introduction programmes were carried out in the Soviet Union.

Those releases effectively allowed the species to leap far beyond the range it had reached naturally from Bohemia.

The animals subsequently established populations across parts of Siberia and Central Asia, with further expansion reaching China and Mongolia and eventually Japan.

The European muskrat story had become an international one.

Why were they so difficult to stop?

The muskrat's success was not based on extraordinary speed or unusual intelligence.

It was a remarkably good match between animal and environment.

They reproduce relatively quickly, live around water and can disperse through connected waterways. Their burrowing lifestyle also allows them to occupy riverbanks and other wet habitats where many terrestrial mammals would struggle.

Imagine a population occupying one stretch of river.

Over time, young animals move outward.

Another stretch becomes occupied.

Then another.

The result is less like an army marching across a map and more like a series of expanding circles connected by waterways.

That distinction matters because connected habitat can make geographical distance misleading.

A location 20 kilometres away might be difficult to reach across unsuitable land but comparatively accessible along a river system.

Then the burrows became an engineering problem

The muskrat's biggest problem for humans was not its appetite.

It was its ability to dig.

In a natural riverbank, a burrow may cause relatively little concern.

But an earthen embankment protecting a canal, railway or low-lying settlement serves a very different purpose.

Muskrats excavate entrances below the waterline and can create tunnel systems inside banks. Repeated excavation can weaken these structures, particularly when populations become dense.

That transformed the animal from an ecological curiosity into an infrastructure problem.

And few places illustrated this better than the Netherlands.

The Netherlands turned muskrat control into a permanent operation

The Netherlands relies extensively on dikes, embankments and other engineered structures to manage water.

An animal capable of creating tunnels through those structures presents an obvious concern.

As a result, muskrat control became an ongoing task, with professional trappers working throughout the year and removing large numbers of animals.

The objective is also different from simply eliminating muskrats from a particular pond.

Authorities have had to focus on preventing populations from expanding and protecting vulnerable water infrastructure.

Belgium, France and Germany have likewise maintained control programmes.

The European Union eventually formally listed the muskrat as an invasive alien species of Union concern in 2017, bringing restrictions intended to prevent its keeping, transport, trade and deliberate release.

The tiny experiment near Dobříš had evolved into a continent-wide management problem.

Britain tried something even more ambitious

Britain's experience offers a particularly interesting contrast.

The British muskrat population did not simply descend from the original Bohemian population.

Instead, muskrats arrived through the fur trade, with escapes from fur farms during the late 1920s helping establish populations, particularly around waterways in the Severn region.

Britain ultimately decided not merely to control the animals but to eliminate the established population.

That required a sustained trapping campaign.

According to research published in the Biological Journal of the Linnean Society examining the eradication of muskrats and coypus from Britain, the campaign continued for years.

By 1939, the established British muskrat population had been eliminated.

That outcome demonstrated something important about invasive species management: eradication can be possible, but timing matters enormously.

Stopping a small, geographically contained population is one challenge.

Trying to remove an animal after it has occupied thousands of kilometres of interconnected habitat is an entirely different one.

What does this mean for us?

The strange journey of Europe's muskrats began with five animals.

There was no continent-wide plan behind their expansion. No single release created millions of animals overnight.

Instead, a combination of reproduction, suitable habitat, waterways, accidental escapes and deliberate introductions gradually transformed a local curiosity into a widespread invasive species.

The story is also a reminder that biological invasions are rarely just about the animal itself.

A muskrat can look harmless.

But put millions of muskrats beside canals, flood defences and engineered embankments, and its burrowing habits suddenly become an infrastructure issue.

That is what makes the 1905 introduction so remarkable.

A decision involving five animals on a private estate helped create a natural experiment that unfolded across generations—and eventually forced European countries to spend decades figuring out how to manage the consequences.