Britain’s ecosystems face a rising threat from invasive non-native species, including pink salmon, purple Asian clams, spaghetti bryozoans, and a deadly nematode worm. These species have been highlighted in a newly updated top 20 invasive species watchlist, compiled by leading scientists from the UK Centre for Ecology & Hydrology (UKCEH).
What Are Invasive Non-Native Species?
Invasive non-native species (INNS) are animals, plants, or microbes that are introduced outside their natural range, often through global trade, travel, and climate change. While not all introduced species become invasive, those that do can harm native biodiversity, disrupt ecosystems, threaten human health, and damage the economy.
The New 2025 Watchlist: Top Invasive Species to Watch in Britain
A team of ecologists has assessed 145 non-native species that pose a serious risk to Great Britain over the next decade. Here are some of the most concerning new entries on the updated list:
1. Pink Salmon (Oncorhynchus gorbuscha)
- Already found in rivers in Scotland and northern England.
- Competes with native salmonids, such as the endangered Atlantic salmon.
2. Pine Wood Nematode (Bursaphelenchus xylophilus)
- A microscopic worm that causes pine wilt disease, killing trees rapidly.
- Spread by the pine sawyer beetle (Monochamus galloprovincialis).
3. Spaghetti Bryozoan (Amathia verticillata)
- A filter-feeding invertebrate forming large bushy colonies.
- Smothers seagrasses, clogs pipes, and disrupts marine food chains.
4. Purple Asian Clam (Corbicula largillierti)
- Fast-reproducing bivalve that clogs water infrastructure.
- Outcompetes native mollusks and threatens freshwater ecosystems.
5. Veined Rapa Whelk (Rapana venosa)
- A predatory sea snail feeding on native mussels, scallops, and oysters.
- Risk to shellfish populations and fishing industry livelihoods.
6. Asian Fan Weed (Rugulopteryx okamurae)
- An invasive seaweed that displaces native algae.
- Decomposes on beaches, affecting tourism and local wildlife.
Why Invasive Species Are a Growing Threat
Globalization and climate change are accelerating the spread of invasive species in the UK. Some species arrive intentionally (e.g., for aquaculture or horticulture), while others are hidden in cargo, plants, or ship ballast water. Warming temperatures allow species from warmer climates to survive and establish in Britain.
Prevention is Key: Horizon Scanning and Public Awareness
According to Professor Helen Roy, lead scientist at UKCEH, preventing the arrival and spread of invasive species is far more effective than trying to remove them once they’re established. That’s why horizon-scanning exercises—like this one—are vital.
“Eradicating invasive species once they are established is extremely difficult and costly,” Roy said. “That’s why early detection and public awareness are essential tools.”
Voluntary contributions from scientists and citizen science efforts—such as public reporting of sightings—are instrumental in managing threats.
A Past Success: The Case of the Yellow-Legged Hornet
The yellow-legged (Asian) hornet (Vespa velutina), first flagged in the 2013 watchlist, is a real-world example of successful horizon-scanning. Thanks to early detection and public reporting, along with rapid response from the National Bee Unit, Britain has so far prevented this aggressive predator from establishing. However, the risk remains high.
Additional Ongoing Threats
The updated list also reaffirms the risks from:
- Beetles like the emerald ash borer, Asian longhorn, and citrus longhorn, known for destroying trees.
- Raccoons, which disrupt native wildlife, damage fruit crops, and may carry rabies and dangerous parasites.
Economic and Environmental Impact
With over 2,000 non-native species already present in Britain, the stakes are high. While only 10–15% become invasive, those that do cost the UK economy nearly £2 billion annually and pose significant environmental and health hazards.
Olaf Booy, Deputy Chief Non-Native Species Officer, emphasized:
“Horizon scanning helps us predict and prevent harmful introductions. Without it, our ecosystems, economy, and health systems face severe consequences.”
How You Can Help
- Stay informed about invasive species in your area.
- Report sightings of unusual plants or animals to local authorities or through national reporting apps.
- Clean your gear (boots, boats, fishing equipment) to prevent the spread of aquatic species.
- Support local and national biosecurity campaigns.
Conclusion
The fight against invasive species is a race against time. With the right tools—scientific insight, public engagement, and strong policies—Britain can protect its precious ecosystems from the next wave of ecological invaders.
➤ Stay alert. Stay informed. Protect biodiversity.
For more information and to view the full report, visit the UK Centre for Ecology & Hydrology:
Horizon-Scanning Report on Invasive Species – UKCEH