Philonthus cognatus

I wouldn't normally recommend Google Lens as an ID tool but might have saved myself a couple of hours if I'd used it first off here. I'm still very inexperienced with Staphs and until Duff gets his Staphs volume published I've only got the Hackston keys to work from (at the time of writing this - I have since acquired Lott keys). My first mistake was judging whether the antennae were on the top of the head or the side. They are clearly on the top of the head - the top of the head goes all the way round the insertion points so they must be. At least that's what I thought. Admittedly the insertion point itself is vertical and under a tiny ridge, but the very base of the antenna is clearly visible from above. Well, apparently not, so I discovered after spending ages keying and re-keying tribe Aleochorinae. Every time I ended up with genus Gymnusa but neither of the two members of that genus were close to my beetle. I had half-suspected it was in Staphylininae and if I ignored the placement of the antennae it keyed to that tribe, but I made another mistake there. (Incidentally, now I've got Lott, I see that there you do have to take the antennae placements as being on the upper surface of the head to get to Staphylininae - no wonder I was confused!)

Annoyingly I did actually notice that there was a tiny bit of the side of the pronotum that was visible from the side, but judged this to be so small as to be insignificant. If only I'd read the footnote at the end of the couplet: "Occasionally this is very slight, e.g. in the very common Philonthus cognatus the epipleura may only be visible very narrowly in the vicinity of the base of the front legs." It even gave me the species for goodness sake! But no, I got thoroughly bogged down in Quedus trying to work out which pore was which before eventually giving up and going back to Aleochorinae...

Only when in desperation I tried Google Lens and it offered me a suspiciously similar picture of a Philonthus I went back and found this comment. Hackston doesn't seem to have a key for Philonthus yet so after all this effort I thought I wasn't going to get it to species level anyway. Thankfully though, the UK Beetles page for cognatus gives enough information to enable this one to be identified confidently. Phew!

This one was in a pitfall trap.

Philonthus cognatus showing pronotum and head, Wendling Beck Environment Project (Norfolk, UK), 17th-18th May 2023

Although that was the first I identified, I had a few staphs in pots waiting for me to identify and this was among them. It had clearly expired before I took its photo but you can just see the bicolored first antennal segment in one of the photos. Good job too as it had been left on a windowsill so was faded when I came to examine it

Philonthus cognatus, North Elmham (Norfolk, UK), 23rd July 2018