Malthodes marginatus

I was unable to make out the shape of the genital segment clearly on this one so cleared it in potassium hydroxide solution for a better view.

male Malthodes marginatus showing genital segment (before and after clearing), North Elmham (Norfolk, UK), 17th May 2020

2x male Malthodes marginatus showing frons and genital segments, Wendling Beck Environment Project (Norfolk, UK), 26th May 2023

male Malthodes marginatus showing genital segment, Whitwell Common (Norfolk, UK), 14th May 2017

This beetle had started going mouldy when I examined it but fortunately the key details were easily visible (including the genital segment although it had a bit of mould growing on it as can be seen below).

male Malthodes marginatus showing genital segment, Wendling Beck Environment Project (Norfolk, UK), 14th May 2025

male Malthodes marginatus, Thursfood Wood (Norfolk, UK), 22nd May 2017

Duff states that only males can be reliably identified but goes on to include females in his key. However this refers to the shape of sternite 9 but he doesn't provide any diagrams and I wasn't entirely sure if I could identify which sternite 9 was. I'm assuming it was one of the internal plates as I could only count 6 external sternites, the last of which had a large rounded notch. Stretching out the internal workings I couldn't identify anything that clearly matched the description of sternite 9 for any species. Duff also refers to the relative length of the elytra and Hackston also includes a provisional key for females which uses this. Based on the elytral dimensions this female appears to be marginatus - which of course is no surprise as this is the commonest species and the only one I've seen that looks like this externally.

female Malthodes marginatus showing side of pronotum, apical sternites (2 views before extraction and one with internal sclerites pulled out) and elytral measurements, Beetley Meadows (Norfolk, UK), 28th April 2025

This was another female and as before it is primarily identified to marginatus based on the porportions of the elytra. Again I struggled to be certain about what sternite 9 was. The last clearly visible sternite only seemed to be the seventh (I'd thought sixth on the individual above but looking at this one I think I can see an extra narrow sternite at the base of the abdomen when looking from the side). Perhaps there are more tiny or barely visible ones and this is the ninth? It's the only sternite I can find that has an obvious incision and I can't find anything inside that seems to match the desciption of its shape. Having said that, if it is the ninth sternite, I'm not convinced the incision is quite half as long as the sternite (but about half, maybe). It can't be guttifer (where it's less than half) as the pronotal disc punctuation is too sparse.

female Malthodes marginatus showing pronotum, elytron and apical sternites (before and after clearing and dissected), Wendling Beck Environment Project (Norfolk, UK), 27th May 2025

I was pretty sure this was marginatus when looking at the genital segment on the dried specimen but it was a bit difficult to be sure if the tips of sternite 9 were expanded or not. After a quick soak in potassium hydroxide this became obvious.

male Malthodes marginatus showing genital segment (before and after clearing), Wendling Beck Environment Project (Norfolk, UK), 28th May 2025