Longitarsus melanocephalus

I found this one inside the house.

female Longitarsus melanocephalus showing elytral humeri and spermatheca, North Elmham (Norfolk, UK), 29th June 2022

male Longitarsus melanocephalus showing elytra, fore tarsus and aedeagus (flat and side views), North Elmham Cathedral Meadows (Norfolk, UK), 12th October 2019

This one was very early in my beetling days and I attempted to identify it using Hackston's key. I made it Longitarsus agilis but realised that was unlikely and contacted the county recorder for advice. He suggested melanocephalus and kindly provided an alternative key which helped me confirm that it was indeed melanocephalus.

Longitarsus melanocephalus, Cranwich Heath (Norfolk, UK), 11th March 2017

I think I would have used the same to identify this, which came to light.

Longitarsus melanocephalus showing elytra, fore tarsus and aedeagus (flat and side views), North Elmham Cathedral Meadows (Norfolk, UK), 22nd April 2019

One point in Duff's key requires an assesssment of whether or not the pronotum has a metallic lustre. This can be really subtle on the species that have it so I've sometimes gone wrong here and overlooked it. This time, possibly for the first time, I made the opposite mistake. Thinking it was rather similar to those beetles which were supposed to have a metallic lustre but where it was only faintly visible, I keyed it as if it did have. I ended up at Longitarsus atricillus and the aedeagus was roughly similar so I labelled it as such. I knew that it was a species I had seen several times but forgot that these were all at one quite distinctive site and it's actually relatively scarce. However, fortunately I reflected on this identification enough to look at it again, and this time I observed that the shape of the aedeagus wasn't quite the same. On atricillus the tip is more onion-dome-shaped than this was and it narrowed slightly below the tip. At that point I realised that the aedeagus - and indeed the general appearance of the whole beetle - was actually a better match for the much commoner melanocephalus. I hadn't yet disposed of the beetle so re-checked it and sure enough melanocephalus does match up.

male Longitarsus melanocephalus showing elytral humeri, fore tarsus and aedeagus (flat and side views), Ling Plantation, North Elmham (Norfolk, UK), 12th April 2022