News article created on 27 July 2021

We've deployed an army of weevils to eat canal menace

An army of 2mm-long weevils has been called-in to prevent the Bridgwater & Taunton Canal from being overcome by a problematic water weed.

Ecologist crouching down on the ground Chantal Collins releases the weevils into the Bridgwater & Taunton Canal

This week our ecologists have released 3,000 weevils into the water at locations along the canal, in the hope that they will eat the invading Water Fern (Azolla filiculoides).


Azolla is a voracious grower and can multiply rapidly, covering the surface of a waterway with thick mats in a matter of weeks. The thick mats can appear as a solid surface sometimes mistaken by dogs and children to be safe to walk on. The mats also reduce light and oxygen levels in the water, harming fish and other wildlife, as well as affecting how boaters and anglers can use the canal.

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.

Given time to reproduce and spread throughout a mat of Azolla, the weevil is capable of clearing entire lakes or canals within a matter of weeks.

A serious threat to local water wildlife

Laura Mullholland, Canal & River Trust ecologist, said: “Azolla can be a serious threat to local water wildlife. With the recent very hot weather there’s a danger that it can grow really quickly and completely take over sections of the canal, so we’re getting the weevils in to combat it.

"The weevils breed really quickly and only eat Azolla. The Bridgwater & Taunton Canal a great place to visit at this time of year, excellent for boaters, walkers, families and people with an interest in wildlife, so I’d encourage you to come and have a look for yourselves.”

A troublesome plant

Originally from the Americas, Azolla can now be found on our waterways, 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.

Each year we spend a huge amount of time clearing species of aquatic weed from the nation’s canals, rivers, reservoirs and lakes. Many of these invasive weeds are freely available to buy as ornamental water plants in garden centres across Britain.