Wren Franklin, a masters student at Bournemouth University, found two of the great silver water beetles (hydrophilus piceus) while surveying animal and plant life in ponds in Blackmore Vale, north Dorset, as part of research for his biodiversity conservation course.
When he checked with Dorset’s county recorder for beetles, he found the only other recorded sighting in the county was in 1821, by one of Britain’s most influential entomologists, JC Dale.
Mr Franklin said: “It was a really exciting discovery, as soon as I found them I knew I’d come across something special.
“Great silver water beetles are often found in the Somerset levels, so this begs the question, have they been hiding undetected in the Blackmore Vale for two centuries or have they recolonised recently whilst looking for new habitats.
“We’ll never know, but it is great to find them using newly created wetland habitat.”
The beetle is the heaviest beetle in the UK and can grow to five centimetres long, but Mr Franklin described it as a “gentle giant” because it mostly scavenges plant material for food rather than as an aggressive predator.
Mr Franklin said he hoped the discovery would help raise awareness of the threats to biodiversity.
He said: “People know about the threats faced by big animals in other parts of the world, but there are also loads of fascinating species in our own neighbourhoods which are equally imperilled.”
