Tasgius ater

I found this pair of copulating beetles on a tree trunk with a third, which I assumed to be the same species, nearby - if I remember rightly it was at the base of the same tree. I retained one - my notes suggest it was one of the pair that I retained but the way I labelled the photos suggests it was the third individual.

At the time I did not have access to a key to Tasgius and Ocytus (I had got it that far using Mike Hackston's keys) but after some correspondence with Mike he provided a key to the two genera, though I can't find that on his new website (but I can now find the German key which I think might be the one he used as a basis). Using his key I identified my specimen as Tasgius ater, though I noted in my correspondence that I had struggled to be sure if I was seeing two sizes of pronotum puncture - there was variation in size but this seemed to be more clinal than two clear size classses. Also, although some punctures were clearly separated from one another by more than the diameter of the puncture, this didn’t seem to be the case across the entire pronotum. My mind was made up by a comment that ater was the only member of the genus having epimera of the pronotum and this, I thought, had epimera.

I didn't retain a specimen and my photos are not clear enough to see the detail I saw under the microscope at the time, and looking back I wondered if I might possibly have made an error. My concern was partly influenced by finding photos of Tasgius ater online that show larger more spaced punctures on the pronotum than are evident in my photos. On the other hand there were other photos at least purporting to show Tasgius ater where the pronotum looks extremely similar to how it does in my photos. I concluded that it might be better to consider this record unproven, at least until I obtained more experience of ater.

Well, I'm updating this in 2024 after finding another ater (confirmed genitalically, see below) and the pronotal puncturing is very similar - so I think my original record is probably safe as that was my main point of concern.

2-3 x Tasgius ater North Elmham Cathedral Meadows (Norfolk, UK), 2nd December 2018

This one was found in a vane trap in my garden. In keying it using Duff I wasn't completely convinced by every step so felt I needed to confirm it by checking its genitalia. I also looked at Lott & Anderson and found it much easier to get to Tasgius/Ocypus using Lott & Anderson vs. Duff, but using Lott & Anderson the shape of the mandible indicated Ocypus rather than Tasgius (though keying it to species still led to Tasgius ater). Based on Lott & Anderson's description of the mandible shape it was a clear-cut Ocypus - there was a clear and obvious tooth. Duff provides views from two angles of the aedeagus for I think all of the Tasgius and Ocypus species so this was hugely helpful for confirmation.

I have included several different angles of the head as I'm still trying to get to grips with the differences between the antenna placement between the different subfamilies.

male Tasgius ater showing head (4 views), pronotum (2 views from above, 1 from side and 1 from below), hind claws, mandible and aedeagus (3 orientations), North Elmham (Norfolk, UK), 21st July 2024