Rhantus suturalis

Brock's two photo guides on British insects assign this species the vernacular name Supertramp. I'm not sure how widely that is recognised.

When I first started making a concerted effort to identify most of the beetles that turned up in my moth trap, the majority of diving beetles were identified as this species. Since then they dried up (until 2024) whereas I started getting regular Colymbetes fuscus which I did not find in the first couple of years or so. This made me wonder if I'd got my early IDs wrong, but although I don't have any specimens to check, the photos seem to be correct. I used Mike Hackston's key which I sometimes found a little confusing, thanks in part to not having understood how to sex them. Duff's key seems simpler in this respect. Starting to get suturalis again in 2024 reassures me they really do occur here!

This one was initially identified using Hackston and then checked using Duff. I found Duff easier to follow in this case.

Rhantus suturalis showing underparts and side border of pronotum, Wendling Beck Environment Project (Norfolk, UK), 14th July 2024

I used Duff for this one which came to light in my garden. Although the underside isn't completely jet black, I think it's black enough to qualify. I took my time figuring this out but having eventually noticed Duff's comments in the introduction to his Rhantus key, I can sex this as a female based on the foretarsomeres not being broadened (the photo of the tarsus is side on, but they didn't look broadened when looking down on them either). The pattern of the pronotum often seems to be impossible to see in photos of live insects but becomes clear when looking under a microscope.

Rhantus suturalis showing pronotum and foretarsus, North Elmham (Norfolk, UK), 25th September 2024

The following were all identified using Hackston's key.

Rhantus suturalis, North Elmham (Norfolk, UK), 16th June 2017

Rhantus suturalis, North Elmham (Norfolk, UK), 10th July 2017

Rhantus suturalis, North Elmham (Norfolk, UK), 16th July 2017

Rhantus suturalis, North Elmham (Norfolk, UK), 17th August 2017

Rhantus suturalis, North Elmham (Norfolk, UK), 18th October 2017

Rhantus suturalis, North Elmham (Norfolk, UK), 24th October 2017

Rhantus suturalis, North Elmham (Norfolk, UK), 2nd August 2018

Rhantus suturalis, North Elmham (Norfolk, UK), 20th August 2020

This one was photographed well before I had access to resources enabling identification of diving beetles and was identified retrospectively a few years later when Brock's guide to Insects was published in 2014. However, despite the word "comprehensive" in this publication's title, suturalis is the only Rhantus covered by the book with no clue given to the existence of other species let alone how to separate them. At the time, therefore, the identification was best regarded as unsafe, although looking at the photo today I suspect it was nevertheless correct.

probable Rhantus suturalis, Bawdeswell (Norfolk, UK), 14th July 2008