Berosus affinis
My first Berosus proved reasonably straightforward to key out.
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male Berosus affinis showing pronotal punctures, underside of abdominal sternites, mesosternal ridge and aedeagus, Wendling Beck Environment Project (Norfolk, UK), 29th October 2022
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male Berosus affinis showing pronotal punctures, underside of abdominal sternites and mesosternal ridge, Wendling Beck Environment Project (Norfolk, UK), 8th September 2023