Atomaria atricapilla

This beetle, about 1.5mm long, came to light in my garden moth trap. I keyed it using Duff and found most couplets worked ok. I found it difficult to see the side margins of the pronotum clearly enough to be sure if there was a single or double margin (I suspect this would have been more obvious had it been double) and I wasn't convinced about the form of the hair on the pronotum. My initial assessment of the pronotal hair was that it was the nitidula-type pattern, which would have made this Atomaria scutellaris. Not convinced I tried the alternative route in the key and this time ended up at Atomaria atricapilla. In the end it was the genitalia that settled it, confirming that it was atricapilla.

male Atomaria atricapilla showing multiple views of antennae, pronotum and aedeagus, North Elmham (Norfolk, UK), 31st May 2025