The River Chess Association (RCA) has made a rare discovery during routine river monitoring in Rickmansworth.
The group confirmed that the creature found in the river on Thursday, August 15, was a cimbex connatus, commonly known as a giant alder sawfly.
Mr Jennings, one of the RCA members who made the discovery, said: “The larva was over two inches in length, one of the biggest found in the UK, along with the May bug and stag beetle larva. It’s a bit of a monster.”
The giant alder sawfly has only been present in the UK since 1997 and, although they are growing in number, are still relatively rare.
When they reach maturity, these sawflies mimic the European hornet in their looks, and devour large amounts of foliage.
The RCA is a group dedicated to monitoring local river activities and protecting wildlife and invertebrates. Its team of volunteers monitor the water quality of the River Chess, which runs through Rickmansworth.
For more information about the group, please visit www.riverchessassociation.co.uk and to find out more about volunteering, visit www.t.ly/soG2k
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