Native Species Released to Tackle Invasive Pests Across Britain

Government scientists are releasing specially bred species into the wild to help control invasive plants and animals that threaten Britain’s native wildlife.

Researchers have been using biological control agents to combat invasive species such as Japanese knotweed, floating pennywort, and Himalayan balsam — plants that choke rivers, outcompete native flora, and damage habitats.

The Department for Environment, Food and Rural Affairs (Defra) has set ambitious targets under its environmental improvement plan, directing the Animal and Plant Health Agency (APHA) to reduce the establishment of invasive species by 50% by 2030.

Olaf Booy, deputy chief non-native species officer at Apha, said: “The science around biological control is always developing. It really works for those species that were introduced quite a long time ago, that we haven’t been able to prevent getting here or detect early and rapidly respond.”

Weevils and Psyllids Used to Reduce Plant Growth

Floating pennywort, which smothers rivers, is being targeted with the South American weevil (Listronotus elongatus). Sites where weevils have overwintered for several years have seen significant reductions in the plant’s biomass.

Japanese knotweed is being tackled using the psyllid (Aphalara itadori), which feeds exclusively on the invasive plant, while Himalayan balsam is being controlled through releases of the rust fungus Puccinia komarovii var. glanduliferae. Defra says early results from these biocontrol trials are encouraging.

“Once the biocontrol agent is working properly, then it should actually start to spread naturally across the range, where the non-native species is, and it will start to bring that population of the non-native species down,” Booy said. “Hopefully, once it starts to establish in the wild, then it sort of starts taking over itself, and the human effort bit starts to reduce significantly.”

Protecting Native White-Clawed Crayfish

The programme also aims to protect threatened native species from invasive competitors. Britain’s white-clawed crayfish has been largely displaced by the invasive American signal crayfish, which carries a deadly plague.

To safeguard the native species, scientists have created “ark sites” — protected habitats free from invasive predators. Hatcheries in Yorkshire and Devon are breeding crayfish for release into these safe locations. More than 1,500 breeding-age crayfish have already been relocated to eight secure sites in Gloucestershire.

Preventing Invasive Mammals From Establishing

Experts are also monitoring medium-sized non-native mammals such as raccoons and raccoon dogs, which are popular pets but can escape into the wild. These species could threaten amphibians, small birds, and other native wildlife.

Currently, owners of raccoons and raccoon dogs do not need to register with the government, though breeding and selling them is prohibited. Officials warn that social media trends portraying raccoons as cute pets could increase the risk of escapes and wild establishment.

“You do see things like raccoons and raccoon dogs popping up on social media and stuff. Particularly raccoons, they’re kind of cute and cuddly, and you could imagine that a TikTok trend might encourage people to think about getting a species like that. Obviously years ago we had the interest in terrapins from the Teenage Mutant Ninja Turtles” Booy said.

He added: “If you have a raccoon, you really need to know how to keep it securely to avoid it escaping. You don’t really want any predators of that sort of size establishing and spreading in the country, because it will have knock-on impacts for biodiversity. But they are also potentially vectors of disease as well.”

Biological Control Reduces Human Intervention

One key advantage of these biocontrol agents is that they reduce the need for labour-intensive removal of invasive plants. By targeting pests naturally, scientists hope to restore ecosystems and give native species a better chance to thrive.

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At Natural World Fund, we are passionate about restoring habitats in the UK to halt the decline in our wildlife.