Floating pennywort is a non-native invasive species, which spreads rapidly and causes major destruction to our waterways. Its large mass depletes oxygen levels in the water, in turn affecting other plants and animals.
Its presence is also felt by boaters and other waterway users, who are unable to paddle or propel their way along the navigation as a result.
South American weevils have never been used to aid in floating pennywort removal before, but research suggests that these small beetles could make a mighty impact.
What are South American weevils?
Imported from Argentina and measuring approximately 5cm in length as adults, South American weevils are a type of beetle which offer a natural and environmentally-friendly alternative to chemical sprays.
How do weevils combat floating pennywort?
These plant-munchers feed and breed amongst the foliage, slowly but effectively reducing its vast quantities which span across our canals and rivers.
If weevils are a non-native species, how is releasing them on our waterways safe?
Along with other collaborators, CABI spent time in Argentina monitoring and observing various insects and pathogens, including the South American weevil.
After ten years of comprehensive testing and research, there was no evidence to suggest that the weevil would attack any other living organisms beyond floating pennywort.
As a result, in 2021 the South American weevil was cleared for combat under a carefully coordinated release strategy along our canals and rivers.
How long do South American weevils live for?
Given that they don't attack other plant species, we expect the weevils to remain in the waterways and feed until the plant has gone.
However, one of the areas we will be assessing during this trial is whether they can withstand the winter months and continue to effectively control floating pennywort into next year.
When will we know if the trial is a success?
Along with CABI and other partners, we will be regularly visiting the release site over the next 12 months to visually inspect the area. CABI will also be continuing with data and evidence gathering along the way.
We hope to see the first signs of improvement at around month two, but this is dependent on a huge number of factors, such as weather conditions and water quality.
Will more weevils be released if this trial is a success?
That's the plan. Watch this space for more updates on this innovative trial.
How you can join the fight against invasive non-native species (INNS)
If you spend time on our canals and rivers, one of the most important things you can do is to remember to Check, Clean, Dry. These steps help stop the spread of harmful plants and animals to a new area, and should always be done before exiting a waterway, even if you are moving to another spot just a few miles away.
If you would like to volunteer on this project with us, we are currently looking for someone to help out with admin and reporting. Please contact Charles Hughes for more information.