Waterways Charity Deploys ‘Natural Army’ Of Wonder Weevils Help Tackle Weed-Clogged Canals

A proven army of 2mm-long weevils has been called in to assist the nation’s canal charity, Canal & River Trust, in the fight against the invasive water weed Azolla, which is particularly problematic this year in South Yorkshire and the East Midlands.

Ecologists from the charity have released around 20,000 azolla-eating weevils (stenopelmus rufinasus) this year along the most weed-clogged waterways. More are due to be released on the Dearne & Dove in Barnsley, the Chesterfield Canal and Grantham Canal over the next week.

Around £700,000 is spent by the Canal & River Trust every year tackling invasive species across its 2,000-mile canal network in England & Wales, to maintain navigation for boaters, paddlers and so that they are in turn available for wildlife.

With the effects of climate change seeing invasive weeds flourish, the Trust is increasingly concerned by the impact and the costs, but proven help is at hand from the ‘wonder weevil’.

Ellie Harker, ecologist at the Canal & River Trust, explained:
"Weevils are without doubt the best way for us to combat this prolific invasive weed. Weevils breed quickly, only eat the Azolla and can be deployed quickly from the water’s edge, limiting the possibility of the weed spreading.

“Weevils offer a natural solution that is safe, self-sustaining and more cost effective than mechanical means of removal needed for removing other invasive plants. These are all important factors as we encounter the effects of climate change with hotter summers and milder winters.”

"Azolla can multiply rapidly and cover the surface of a waterway with thick mats of weed in a matter of weeks. These mats can form a green surface and sometimes even be mistaken as being solid to walk on. Light and oxygen levels in the water are also reduced, harming fish and other wildlife and affecting how boaters, paddlers and anglers can use the canal.

"Given time to reproduce and spread throughout a mat of Azolla, these long-snouted beetles with their insatiable appetite for Water Fern or Fairy Fern (azolla filiculoides), are capable of clearing weed from entire lakes or canals within weeks.

“Each year our charity spends a huge amount of time clearing species of aquatic weed from the nation’s canals, rivers, and reservoirs and they can be a serious threat to local water wildlife, cause problems for boaters and paddlers, and trap rubbish.

“The recent hot weather has seen some sections of our waterways become inundated by these invasive weeds that grow really quickly, and with climate change bringing warmer weather it’s becoming a serious endemic issue. We have to use all the tools at our disposal – including this army of weevils – to keep our canals available to all.”

Azolla is a small, aquatic, free-floating fern native to the warm temperate and tropical regions of the Americas and until 2014 it was available to buy as an ornamental garden pond plant. Azolla was one of five aquatic weeds banned from sale in the UK in 2014. The wildlife and countryside act makes it illegal to plant or cause it to grow.

Having found its way into the Trust’s waterways, Azolla can now be found often in large clumps. Also known as fairy moss, or water fern, Azolla isn’t a true moss, but an aquatic fern. It grows very rapidly making it one of the most troublesome invasive plants.

Individually the weevils (Stenopelmus rufinasus) consume a relatively small amount of Azolla, however they breed to produce very large populations which, together, will feed extensively, until sections of Azolla start to die and sink to the bottom, where it is further decomposed.