Corticarina minuta

I keyed this using Duff and when I got to the couplet where I had to choose between "Body pitchy to dark brown (except due to immaturity)" and "Foreparts (at least) ferruginous" I opted for the latter. That led me to Corticarina truncitella but I wasn't convinced that was right. Taking the other option led to minuta which I believe is the commonest species in the genus and I suspected that might in fact be the correct ID. Checking the genitalia confirmed that this was indeed the case. The number of visible sternites is one of the criteria used to separate the genera in this group but I find this hard to see on a dead dried insect - it's much clearer when the abdomen has been macerated.

male Corticarina minuta showing antenna, pronotum (with and without measurements), fore tibia, elytral hairs, sternites (before and after clearing) and aedeagus (side and flat), North Elmham (Norfolk, UK), 3rd September 2022

This is the same beetle side-by-side with a Cortinicara gibbosa collected a couple of weeks later. The minuta was 1.6mm long.

male Corticarina minuta, North Elmham (Norfolk, UK), 3rd September 2022 (left) with Cortinicaria gibbosa, Bintree Mill (Norfolk, UK), 17th September 2022 (right)

This female was a much darker insect (especially the foreparts) and so keyed to minuta more easily - which was helpful as I didn't have the aedeagus to back up my ID.

male Corticarina minuta showing pronotum, sternites and elytral hairs, North Elmham (Norfolk, UK), 6th September 2023