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Army of weevils eat canal menace

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

This week our ecologists have released 3,000 weevils into the water at locations along the 16-mile canal, in the hope that they could 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. This reduces light and oxygen levels in the water, killing 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 as a community will feed extensively, until sections of Azolla start to die and sink, where it is further broken down by other feeders. 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.

Serious threat

Laura Plenty, Canal & River Trust ecologist, said: “Azolla can be a serious threat to local water wildlife. With the 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, so should be extremely effective. The Gloucester & Sharpness Canal is 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.”

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.

Last Edited: 01 August 2014

photo of a location on the canals
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