The Invasion Within the Invasion: Alien Crayfish Are Fighting for Europe’s Rivers

By newspaperport on October 24, 2026 • ( Leave a comment )

New research reveals that invasive crayfish species are not only threatening Europe’s native freshwater wildlife. They are also competing with one another — and the newest arrivals may have the advantage.

FLI Institute | Biology, Ecology & Environmental Innovation | October 24, 2026

Europe’s freshwater ecosystems are experiencing an invasion within an invasion.

For more than a century, North American crayfish have been spreading through European rivers, lakes and canals, displacing native species and transforming aquatic habitats.

Now scientists have discovered that the invaders themselves may be heading for a confrontation.

A study published on October 24, 2026, in the scientific journal Hydrobiologia compared three invasive crayfish species and found significant differences in their behavior, habitat preferences and ability to explore unfamiliar environments.

The findings suggest that some of Europe’s established invasive crayfish populations could eventually be displaced by newer arrivals.

In other words, the invasion is evolving into a competition between invaders.

Three Species, One Continent

The researchers examined three North American crayfish species that have established themselves in Europe.

The first was the spiny-cheek crayfish (Faxonius limosus), one of Europe’s oldest invasive crayfish species. It was introduced in the nineteenth century and has since spread widely.

The second was the red swamp crayfish (Procambarus clarkii), originally from the southern United States and northern Mexico. It is known for its adaptability, aggressive behavior and ability to colonize different freshwater environments.

The third was the marbled crayfish (Procambarus virginalis), a particularly unusual species capable of reproducing without males.

Marbled crayfish reproduce through parthenogenesis, meaning females can produce genetically very similar offspring without fertilization.

This extraordinary reproductive strategy allows a single female, under suitable conditions, to establish a new population.

The three species represent different invasion strategies.

But what happens when they encounter one another?

The Laboratory Experiments

Researchers from Polish scientific institutions investigated how the three species selected habitats and shelters.

They tested preferences for different sediment sizes, shelter dimensions and empty mussel shells.

These characteristics are important because crayfish spend much of their lives close to the bottom of rivers and lakes.

They use shelters to avoid predators, protect themselves during vulnerable periods and compete for territory.

The experiments revealed substantial overlap in habitat preferences.

All three species preferred sediment with particles approximately two millimeters in diameter.

The marbled crayfish, however, was less selective and also tolerated somewhat coarser material.

The spiny-cheek crayfish showed stronger preferences for particular shelters.

The red swamp crayfish moved more frequently between available habitats and explored its surroundings more actively.

These differences may help determine which species succeed when multiple invaders occupy the same waterways.

The Aggressive Explorer

One of the most interesting findings concerned the red swamp crayfish.

The researchers found that this species was generally more mobile and exploratory than its competitors.

It frequently moved between different substrates and shelters rather than remaining committed to one preferred location.

This behavior could provide an advantage when colonizing new environments.

An animal that explores more widely may discover food, shelter and suitable habitat before its competitors.

The researchers also noted that previous studies have documented the red swamp crayfish’s aggressive behavior.

Together, these characteristics may make it particularly successful in newly invaded habitats.

However, exploratory behavior also carries risks.

Moving frequently can increase energy consumption and expose an animal to predators.

Evolutionary success depends on whether the benefits outweigh the costs.

The Marbled Crayfish: A Different Kind of Threat

The marbled crayfish followed another strategy.

Rather than being the most mobile, it was the least selective.

It accepted a wider range of substrates and shelters.

This flexibility may allow it to survive in environments that other crayfish find less suitable.

Its reproductive biology creates an additional advantage.

Because females reproduce without males, a single introduced individual can potentially establish a population.

The combination of habitat flexibility and unusual reproduction makes the marbled crayfish a particularly concerning invasive species.

The researchers suggest that it could eventually become one of the most successful of the three species examined.

But this remains a prediction, not an outcome already demonstrated across Europe.

Could One Invader Replace Another?

The study’s central finding is that the three species have overlapping environmental requirements.

They often prefer similar habitats and shelters.

This creates opportunities for competition.

The researchers suggest that long-term coexistence may be difficult in some environments.

Newer invaders, particularly the red swamp crayfish and marbled crayfish, may eventually displace established spiny-cheek crayfish populations.

However, the experiments primarily examined habitat selection and exploratory behavior.

They did not demonstrate a continent-wide replacement already taking place.

Real-world outcomes will depend on temperature, food availability, reproduction, predation and other environmental factors.

Nevertheless, the research identifies mechanisms that could help explain future changes in European crayfish communities.

An Unexpected Alliance With Another Invader

The experiments also revealed an intriguing connection between invasive crayfish and invasive freshwater mussels.

Some crayfish preferred empty shells of the Chinese pond mussel (Sinanodonta woodiana) over shells of native European mussels.

This suggests that one invasive species can unintentionally provide useful habitat for another.

Ecologists sometimes refer to this phenomenon as facilitation between invasive species.

An introduced organism changes the environment in ways that benefit another introduced organism.

Such interactions can make biological invasions more complicated than a simple struggle between native and non-native wildlife.

Entire networks of introduced species may influence one another.

Why Europe’s Native Crayfish Remain at Risk

Competition between invasive crayfish does not necessarily benefit native European species.

North American crayfish can carry the pathogen responsible for crayfish plague, a disease that has devastated native European crayfish populations.

Invasive crayfish can also consume aquatic vegetation, disturb sediments, compete for shelters and affect other freshwater organisms.

Even if one invasive species replaces another, the ecological pressures on native wildlife may continue.

The arrival of more adaptable invaders could make freshwater conservation even more difficult.

The Future of Environmental Monitoring

The research offers valuable information for conservation authorities.

Understanding which habitats different invasive species prefer can help identify waterways most vulnerable to colonization.

Monitoring programs could focus on sediment composition, shelter availability and areas where invasive populations overlap.

Future research may combine behavioral studies with environmental DNA sampling and automated monitoring technologies.

Such approaches could improve early detection and help authorities anticipate changes in invasive species distributions.

The Leadership Lesson: Competition Never Stands Still

The findings also provide an interesting analogy for business and innovation.

An established competitor may dominate a market for decades, only to face a new entrant with a different strategy.

The spiny-cheek crayfish represents the established invader.

The red swamp crayfish explores aggressively.

The marbled crayfish succeeds through flexibility and extraordinary reproductive capacity.

Each follows a different path to survival.

In business, similar differences emerge between established companies, aggressive market entrants and highly adaptable newcomers.

The most successful strategy depends on the environment.

And the competitive landscape can change even when the original market appears stable.

A New Chapter in Europe’s Biological Invasions

The study demonstrates that biological invasions are dynamic processes.

Introduced species do not simply arrive, establish themselves and remain unchanged.

They encounter new competitors, exploit unfamiliar resources and alter the structure of ecosystems.

Europe’s freshwater crayfish communities may therefore continue changing as new invasive populations expand.

The next ecological disruption may not come from an entirely new species.

It may come from one invader replacing another.

In Europe’s rivers, the battle for survival is no longer simply between native species and outsiders. Increasingly, the invaders are competing for control of the same territory.