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Bidessus minutissimus in Herefordshire

It was a chance visit to an abandoned limestone quarry on the English/Welsh border in July of this year which led to the surprising discovery of the Diminutive Diver Bidessus minutissimus; the first English record since 1908.

Having met Tarmac's environmental manager (Bernie Higgins.) for the south-west on a site tour of the working quarry at Wellington, in Herefordshire we (a botanist, Herpetologist and lepidopterist) were invited to one of their abandoned Silurian quarries. The fenced off quarry pool is 160 metres in by 40 metres with a maximum of four metres in depth. It is incised by about 20 metres below the quarry base with very steep sides; mostly at 50° with large broken angular rocks. Access to the pool shore is possible only in a few places and large parts of the pool are just inaccessible except by rock climbers!

The quarry activity ceased in the late 1990s and the pool formed some 20 years before, so it has been maturing for 40 years. Angular rock of various sizes occupies the majority of the margins. These are covered by algal growth; there are no emergent plants but there are extensive beds of stonewort Chara sp. and floating the macrophyte broad-leaved pondweed Potamogeton natans.

Fortunately at the one place where access is relatively easy there is a bit of gravely beach and shallow shelve and this is where I focused my netting. Dipping amongst the stoneworts produced clouds of black anaerobic sediment and few beetles except for the cherry stone beetle Hyphdrus ovatus, which was abundant. A more diverse assemblage of beetles was found in the very shallow margins amongst leaf litter, gravel and tight bundles of willow roots. Large numbers of Hydroporus sp. were present which all turned out to be Hydroporus planus, with a scattering of Haliplus spp. with both H. obliquus and H. confinus being present. I also netted and collected Graptodytes pictus which is 2.2mm in length which encouraged me to look out for the smaller diving beetles.

It was in the afternoon that I decided to return to this more productive dipping spot and noticed a particularly small diving beetle swimming around the tray. I had to capture it quickly before it disappeared into the leaf litter never to be seen again! When I looked at my specimens back home under the microscope I noticed this tiny diving beetle which was half the size again to G. pictus; I suspected I might have something special. On measuring it was below 2mm which distinguishes from Hydroglyphus geminus and there were furrows on the pronotum extending half way down the elytra, which indicated to me that it may be Bidessus minutissimus. This was duly confirmed by Professor Garth Foster. In total 17 species of beetle were recorded from the quarry pool.

A transcript from Latissimus Magazine with kind permission of the editor.

An extremely small and rare diving beetle (Bidessus minutissimus)