When it comes to choosing a home, the brown diving beetle is fussier than most. First he needs water, but it has to be swift flowing. It also needs to be shallow with no over-hanging vegetation. And as if that isn’t enough - the river bed must be made of flint or gravel.
With such specific requirements it should come as no surprise to discover that Agabus brunneus (to give him his scientific name) is only found at three sites in the UK. One of these is the Portreath Stream in Cornwall.
The Environment Agency recently took over responsibility for managing flood risk on the Portreath Stream and has devised a method of routine maintenance which aims not only to reduce the risk of flooding to local residents, but also improve the habitat of this rare beetle.
All trimming of vegetation and removal of debris from the channel is now done by hand to avoid disturbing the gravel bed of the stream. Overgrown material is cut and then removed from the site for disposal. Whenever possible, Agency staff will work from the riverbanks to reduce trampling the riverbed gravels.
The life history of Agabus brunneus is still something of a mystery, but it is thought the beetle lives, for part of the time, in the gravel beds of streams. A predator, it feeds on small invertebrates.
Measuring only 9 mm in length, the chocolate-brown beetle is vulnerable to pollution, changes in drainage systems and over-abstraction of water. It is also susceptible to the shading of streams by ungrazed vegetation.
Because it is so rare, the brown diving beetle is listed as a priority species by the UK Biodiversity Action Plan and is included in Natural England’s Species Recovery Programme. The only other UK sites where it occurs are in the New Forest and Poole, Dorset.
‘We’re lucky to have such a rare and unusual creature living in the Portreath Stream and will do all we can to help maintain the population of this beetle as part of our flood risk maintenance of the watercourse,’ said Adrian Brown for the Environment Agency.
The Portreath Stream includes a Site of Special Scientific Interest (SSSI), designated for the many mosses and liverwort plants that grow in the poor metal-rich soil. The Agency’s new management of the riverbanks is expected to benefit these rare and unusual plants. Before introducing its new works programme the Agency sought the advice of Natural England and a beetle expert at the University of Plymouth.