Anotylus nitidulus

Once common but apparently much declined - I'm not sure how common it is now?

I had some difficulty keying these. The punctures on the clypeus were sparse and not particularly strong but it was difficult to see them and the other punctures on the head to compare. However my impression was that they were sparser and weaker than those on the vertex, this being clearer on some than others. This had suggested inustus which I had previously identified (though am now in doubt about that) but all four were small so I wasn't convinced and suspected that they were in fact nitidulus. The pair of patches of microsculpture on the head varied in size, being joined together on one but nowhere near as extensive as on clypeonitens. I struggled to make out the detail of the terminal sternites as shown in Lott - on at least two of my specimens there was a thin segment (or bit of a segment?) between the final normal-sized sternite and the much narrower pointed one at the apex, but this didn't seem to be quite the same shape as shown in Lott's diagram for nitidulus (or anything else). I did eventually manage to isolate this on one of them and view it more clearly, and in fact it does match Lott's diagram. The dark sclerotised portion has a shallow central dip but within this dip there is a more membranous and thus hard to see central lobe which gives it precisely the shape shown by Lott.

I was only really satisfied naming these nitidulus after finding that the German Beetles of Europe coleonet.de website showed the male genitalia for each of the Anotylus species under consideration. All four of mine were males and the diagram and photos of nitidulus genitalia at coleonet.de were a strong match for mine in both side and flat views, whereas those for inustus (and other contenders) were quite different.

male Anotylus nitidulus showing head, pronotum, elytra and aedeagus (flat and side views), Wendling Beck Environment Project, 11th September 2023

This one was accidentally squashed (lightly) when potted. None of the important characters were damaged and in fact it's probably the one with the most reliable overall size measurement as it didn't contract or bend up on death.

second male Anotylus nitidulus showing head, pronotum, elytra and aedeagus (flat and side views), Wendling Beck Environment Project, 11th September 2023

third male Anotylus nitidulus showing head (2 views), apical sternites and aedeagus, Wendling Beck Environment Project, 11th September 2023

It was this one where I finally managed to connect what I could see of the apical sternites with the diagram in Lott. The narrow apical sternite is slightly damaged - it did appear to be slightly divided but not as much as shown here. This was also the one that showed more extensive microsculpture behind the clypeus than the others showed.

fourth male Anotylus nitidulus showing head, pronotum, apical sternites (2 views, second with relevant sternite isolated) and aedeagus (side and flat views), Wendling Beck Environment Project, 11th September 2023

I later discovered that I had another from my own garden moth trap taken just a couple of nights earlier. This also keyed to nitidulus and was confirmed with reference to the eighth sternite and genitalia. Again the central lobe on the eight sternite was membranous so difficult to see after clearing the abdomen in potassium hydroxide, but under high power magnification it was clearly visible (arrowed in red in the image below). It's perhaps also worth pointing out that the larger side lobes visible in the photo that don't match the diagram in Lott (arrowed in yellow) are hidden behind the seventh sternite when in situ - the diagrams are as seen in situ but I am personally unable to see these details as it's black on black without isolating the relevant sternite after clearing. The region between the parameres (?) of the aedeagus wasn't quite as before but I think this was because I'd accidentally pulled some of the middle bits out - the parameres themselves (if that's what they are) were the right shape.

male Anotylus nitidulus showing head, pronotum, eighth sternite and aedeagus (side and 2 flat views), North Elmham, 9th September 2023

Before finding or identifying any of these nitidulus I had caught a similar insesct in a pheremone lure trap set for Lunar Hornet Moth Sesia bembeciformis, though I'm not sure if beetles arriving in pheremone lure traps are attracted to the pheremone or just drop in as they're flying through, or even attracted to the coloured plastic lid?

When I looked at it I had just examined an Anotylus rugosus and this was obviously smaller. I used Lott to key it and had a couple of difficulties. The first was deciding if the sides of the pronotum were crenulate or not (or with "very feeble crenulations toward hind angle"). It certainly wasn't like the rugosus I'd just examined - much less obviously crenulate. I'd say it had "feeble crenulations" but all along the sides not just towards the hind angles. Anyway, the crenulated option was eliminated once I looked at the options.

The next and biggest challenge was deciding between nitidulus and inustus. I didn't show up clearly in the photo but looking at it the punctures on the clypeus seemed not only sparser than those on the vertex but also clearly less strongly punctured, so that pointed to inustus rather than nitidulus. The elytra look paler in the live photos than they do on the specimen after death - they now look almost black (completely black in some lights). They certainly weren't ever light brown as is said to be "usually" the case on nitidulus, though having now seen some nitidulus I think "light" is an exaggeration. I felt it was a better fit I think for inustus for which Lott describes the elytra as "occasionally light brown".

My only concern was the size which seemed rather less than 3mm. The actual length of the dried up specimen was just 2.0mm, but the specimen was consertinaed with the head, pronotum, abdomen base (where covered by the elytra) and the rest of the elytra all at different angles - measuring the four lengths separately added a bit, but still well short of 3mm. So then I compared the relative length of the exposed abdomen to the length of the elytra and compared this to how it looked when it was alive - it was clear that the abdomen had contracted significantly after death (as seems to be typical for rove beetles). Adjusting my measurements so that the exposed abdomen was in the same proportion to the elytra as it was in the live photos brought the total measurement up to nearly 3mm. Probably a stretch to get it over the 3mm mark, but close enough for me to feel it perhaps wasn't a deal-breaker considering the other characters that I thought pointed to inustus. Somewhat tentatively, I therefore identified it as inustus, retaining the specimen in case further experience helped firm things up (or in case anyone else wanted to look at it). I hadn't been able to see the details of the eighth sternite so imagined it was probably a female, and at this point I had not come across the German website which showed the male genitalia.

Subsequently, when I found Anotylus nitidulus, my experience with this species cast doubt on my identification of this one as inustus. The punctures on the clypeus of the confirmed male nitidulus appeared to me to be sparser and weaker than those on the vertex, although I found this very difficult to see clearly. The elytra varied but looked similar to this one, or darker, in the live photos, although the colour was perhaps easier to detect on the specimens than had been the case with this one. I felt that this significantly weakened my case for calling this one inustus and left wider open the possibility that it was in fact nitidulus, and (forgetting that I still had the specimen) decided I could not consider the identification proven either way. Later I realised I had in fact still got the specimen, and moreover it was a male which I had not realised originally. Detaching the tip of the abdomen and clearing it in potassium hydroxide I was now able to examine the eighth sternite and genitalia, and this enabled me to confirm that it was another nitidulus (I didn't take a picture of the eighth sternite but it was exactly as the individual above).

male Anotylus nitidulus showing pronotum, antennal base, head, elytra and aedeagus (2 views), North Elmham, 3rd July 2023