Leiopus linnei

Leiopus nebulosus sensu lato used to be known as Black-clouded Longhorn Beetle, but since it has now been split into two species (Leiopus nebulosus sensu stricto and Leiopus linnei) I'm not sure what happens with the vernacular names. Wallin et al.* is a the paper where linnei is described and is a really useful resource for identifying this species pair.

* Wallin et al. (2009). Two sibling species of Leiopus Audinet-Serville, 1835 (Coleoptera: Cerambycidae) from Europe: L. nebulosus (Linnaeus, 1758) and L. linnei sp. nov. Zootaxa 2010: 31– 45. Accessed here.

This one was found by sweeping vegetation beneath an oak tree. I had found my first Leiopus quite difficult to identify but eventually settled on Leiopus nebulosus. Compared to that, this one had much more obvious dark spots on the pronotum and, although I'm still unclear as to exactly where you're meant to measure it, the frons was wider (in range, if I'm measuring it in the right place, for linnei and wide for nebulosus). The punctures on the pronotum, denser at the middle, were also stronger than on the previous one, so before examining the genitalia I had a pretty good idea that it would turn out to be the other one, linnei. The apical sternite hairs supported this ID as did the shape of the spermatheca, clearly widened at the base.

female Leiopus linnei showing close-ups of pronotum, frons, sternite 7 and spermatheca, Wendling Beck Environment Project (Norfolk, UK), 4th July 2024

This was my first Leiopus and I encountered a few difficulties working out if it was nebulosus or linnei using Duff. The only difference in pattern described is in the pronotum where it's supposed to be uniformly covered in grey pubescence, without ochreous spots, in nebulosus, and "covered with a mixture of brownish and ochreous pubescence forming a pattern of spots or a weakly defined median band" in linnei. Mine doesn't look uniform, and I would say the pale pubescence was buff not grey, but there aren't clear spots like there are on many photos of linnei, and on close inspection under the microscope the colour is uniform - the apparent variation being down to variation in hair density and thickness (so with more or less of the black base showing through) not hair colour. Duff describes differences in the width of the frons measured between the lowest points of the eyes. The eyes aren't perfectly round so near the bottom of the eyes there is a bit of a corner. I'm guessing Duff is measuring the frons between these corners? Otherwise if you measure from the very bottom of the eyes your practically going round the sides of the head and I'm not sure that's even the frons still. I'm not sure why he doesn't measure where the eyes are closest as that seems less ambiguous to me, but maybe the difference between species isn't as strong there? Anyway, taking the bottom corners of the eyes the distance is 1.04 mm, so comfortably within the range for nebulosus and marginally outside the range for linnei - but if you measure the distance between the very bottoms of the eyes it would be well outside the range for nebulosus and into clear linnei territory if not beyond. Without comparative material I couldn't do anything useful with the relative curvature of the frons which Duff refers to.

Tergite 8 is helpfully referred to by Duff as a genital sclerite - which gave me confidence that I hadn't miscounted tergites, given its similarity to the apical external tergite which I think is tergite 6. I thought it matched nebulosus best: it was 0.84 mm long - supposed to be c. 0.8 mm for nebulosus and about 1.0 mm for linnei. At the time I felt that the length of the hairs seemed to fit nebulosus better - longer on linnei. My only hesitation here was that it didn't seem to be appreciably more glabrous in the centre as in the diagram in Duff for nebulosus. An additional factor that I did not consider at the time is the shape of the tergite - in the Zootaxa paper the tergite shown for linnei is more pointed (less rounded) than that of nebulosus. Mine was closer to that shown for linnei, though perhaps not quite as pointed (however I don't know if the shape of this tergite is important).

Looking at the genitalia the problems continued. Firstly there are supposed to be differences in the shape of the parameres. My specimen has asymmetrically rounded tips to the parameres and is fairly well swollen at the base, which should point to linnei. But the shape doesn't quite match the diagram in Duff. Thanks to Mike Hackston's key I found the Zootaxa paper where linnei is first described. Looking at the photos of parameres in there I wasn't sure I could make sense of the described differences, so whilst I felt this looked better for linnei to the extent that I understood them, it wasn't clear enough to me to over-ride other characters pointing to nebulosus. The median lobe would clinch it, I thought...

The shape of the apex of the median lobe is different between the two species - rounded in nebulosus and pointed in linnei - this should be straightforward... But what I take to be the median lobe comprises two parts, one in front of the other, and guess what - the front one in my specimen was pointed, exactly the shape shown in Duff for linnei and the rear one was rounded, more-or-less the shape shown in Duff for nebulosus. The back one was slightly longer - but only marginally so - so I figured that was probably the one to be looking at, but I wasn't confident. The Zootaxa paper has photos, and the photo of nebulosus shows both a rounded rear part and a more pointed, or at least angled, front part. The two parts are not clearly discernible from one another on the linnei. As the front part of the nebulosus was somewhat pointed and only the rear part was completlely rounded, I concluded that it must be the rear part that was important. So after a rather tortuous journey, and with some remaining unanswered questions, I became reasonably confident this one was nebulosus. Subsequent experience with the female Leiopus linnei above increased my confidence as the difference in pronotum (pattern and punctures) and frons width seemed evident.

However, this was not the end of the story, as I subsequently trapped another Leiopus which had a very similar pronotum pattern and frons width to the this "nebulosus", but when I examined its genitalia it proved to be a female linnei. This prompted me to review the male nebulosus and this time I had a look at the coleonet.de website. As well as using some of the images from the Zootaxa paper, this showed an additional image of a linnei median lobe, and on that one you can clearly see both front and rear part - and it is only the front part that is pointed, not the rear. So in fact it is the front part, not the rear part, that is important (which in hindsight probably makes more sense). Although the front part does appear to be a bit angled at the centre on nebulosus (more so than shown in Duff), it's not nearly as pointed as it is on linnei. Mine was clearly pointed, so I am now satisfied that it was linnei, not nebulosus.

male Leiopus linbei showing close-ups of pronotum, frons (from front and side), tergite 8, parameres and various views of median lobe (lastly with parameres), North Elmham (Norfolk, UK), 2nd August 2022

This is the female that led to me re-examining and re-identify the last one. Fortunately both sexes seem to be resolvable with reference to genitalia or spermatheca, but I'm still confused by the external features. Maybe that will become clear if I ever find a real nebulosus.

female Leiopus linbei showing pronotum, frons and spermatheca, North Elmham (Norfolk, UK), 18th July 2025