We're calling on thousands of weevils to help battle invasive weed on the Grantham Canal

Why are we using weevils?

The 2mm-long weevils have been released at the canal to eat the invasive North American water fern (Azolla filiculoides). The weed can be particularly problematic to the canal network due to its voracious growth which, if left unchecked, can cover the surface of a waterway with a thick weedy mat. This reduces light and oxygen levels in the water, killing fish and other wildlife.

The weevils are an effective natural means of tackling the problem of water fern. They are at their most active at this time of year and breed quickly so they can very rapidly munch their way through a very large mass of the water fern. The weevils are known to feed exclusively on azolla and don’t cause damage to other native species.

Encouraging results

Reanne Bower, our ecologist, said; “Water fern was first introduced to the UK by the Victorians as an ornamental plant for ponds but, over the years, has spread into the nation’s watercourses. As the weather gets warmer it’s likely that we’ll see a rapid acceleration in the growth of the weed so now is a good time to release the weevils and prevent it from spreading along the canal.

“We’ve introduced weevils on a number of canals over the last few years and have seen some encouraging results, so we hope that by releasing some at targeted spots on the Grantham Canal we’ll be able to reduce the weed and protect wildlife within the canal”.