Tiny weevil used to fight invasive water weed
26 August 2010
A tiny weevil just 2mm long is being pressed into service in the fight against giant rafts of water fern (Azolla filiculoides) clogging a Somerset waterway.
The invasive weed has become a serious problem at Maunsel Lock on the Bridgwater and Taunton Canal, out-competing native plants and forming dense mats across the water's surface. Introduced by the Victorians as an ornamental pond plant, water fern has escaped from gardens to become a major nuisance on rivers, ponds and canals across the country, choking out oxygen so fish and other wildlife cannot survive.
Now however British Waterways is harnessing the fern's natural predator in its native North America, the azolla weevil (Stenopelmus rufinasus), to help it tackle the weed before it spreads. The weevil eats nothing but water fern, and thousands are being released into the Somerset canal in the hope that they will tackle the weed without the need to resort to chemicals.
'Introducing weevils to the canal acts as a natural pre-emptive strike in getting rid of this weed,' said Robert Randall, an ecologist for British Waterways. 'If we don't act now there is a danger that birds may inadvertently transfer the weed to the rest of the canal. Then it will be much harder to contain the spread.'
The weevil doesn't survive UK winters and has been used successfully to control water fern before, both here and in South Africa. British Waterways spent more than £400,000 last year on tackling infestations of water fern and other aquatic weeds, largely escaped from domestic ponds.