Hydrobius fuscipes

Using both Hackston and Duff keys this is usually quite a straightforward beetle to identify. However it seems that things have become more complicated as the species is now split into three: fuscipes, rottenburgii and subrotundatus. All of the following individuals were identified as fuscipes using one or other key and without knowledge of the split. I don't know how to tell rottenbergii but it's supposed to live in coastal rock pools so none of mine (all from inland locations) are likely to be that, and the only information I have about subrotundatus is that it used to be regarded as a variety of fuscipes and as such, Duff describes it as a "shorter and more convex form with darker legs." There is some variation among my photos in how dark the legs appear, though I suspect that has as much to do with how the photos were taken as it does with actual darkness of the legs. For now my working assumption is that they're all fuscipes. It's by far the most frequent member of the family to be attracted to light round here.

Hydrobius fuscipes, North Elmham (Norfolk, UK), 30th July 2022

2x Hydrobius fuscipes, Wendling Beck Environment Project (Norfolk, UK), 20th August 2021

Hydrobius fuscipes, North Elmham Cathedral Meadows (Norfolk, UK), 11th June 2018

Hydrobius fuscipes, North Elmham Cathedral Meadows (Norfolk, UK), 10th July 2021

Hydrobius fuscipes, North Elmham Cathedral Meadows (Norfolk, UK), 19th August 2018

Hydrobius fuscipes, Wendling Beck Environment Project (Norfolk, UK), 2nd August 2021

Hydrobius fuscipes, Wendling Beck Environment Project (Norfolk, UK), 25th September 2021

Hydrobius fuscipes, North Elmham (Norfolk, UK), 9th September 2021

2x Hydrobius fuscipes, North Elmham (Norfolk, UK), 10th August 2020

Hydrobius fuscipes, North Elmham (Norfolk, UK), 10th July 2022

2x Hydrobius fuscipes, North Elmham (Norfolk, UK), 14th July 2018

Hydrobius fuscipes, North Elmham (Norfolk, UK), 17th July 2020

Hydrobius fuscipes, North Elmham (Norfolk, UK), 19th July 2018

Hydrobius fuscipes, North Elmham (Norfolk, UK), 20th July 2018

Hydrobius fuscipes showing close-up of scutellum, Wendling Beck Environment Project (Norfolk, UK), 6th July 2023

Hydrobius fuscipes, North Elmham (Norfolk, UK), 21st July 2018

2x Hydrobius fuscipes, North Elmham (Norfolk, UK), 23rd July 2018

2x Hydrobius fuscipes, North Elmham (Norfolk, UK), 26th July 2018

Hydrobius fuscipes, North Elmham (Norfolk, UK), 8th July 2018

Hydrobius fuscipes, North Elmham (Norfolk, UK), 2nd August 2018

Hydrobius fuscipes, North Elmham (Norfolk, UK), 16th July 2022