Ptomaphagus subvillosus

This was one of the first beetles to be caught in my home-made vane trap. At first I had no idea what family it was in, but I saved some time keying it to family by running it past Google Lens. The only really similar matches were beetles in the genus Ptomaphagus, so I turned to the Leiodidae key in Duff. Rather than jump straight to Ptomaphagus, I decided to key it to subfamily and genus first - just because it looked like Ptomaphagus didn't mean it was. To use Duff's key to Leiodidae subfamilies you need to establish if the beetle has a transverse occipital crest or not - this, apparently, should have one. Now I'm not entirely sure what a transverse occipital crest is but the glossary tells me it's a transverse ridge on the back face of the head. Given the top of the head merged smooothly into the pronotum, was I supposed to remove the head to see this? It's unusual I think for Duff's key (or any key) to require the head to be removed before you can get past the first couplet in the family key, so surely not? Should I have been able to see it from underneath? I couldn't see anything I would describe as a transverse ridge at the back of the head looking from above or below, so I removed the head and still couldn't convince myself I could see what was being referred to here. The back of the head extended over the hind face as a sort of lip, but surely that wasn't what's being referred to. The central section of this seemed to be lifted slightly so maybe this was the ridge, but 63x power it was only vaguely visible from certain angles and only after the head had been removed to expose the rear face. If I took there to be no occipital crest then it would have keyed to genus Colon, which didn't look right. Hackston's key was helpful here - this elimiates Colon on the first couplet based on the number of sternites visible. So it wasn't Colon, so I had to assume it had an occipital crest, and that being so it did indeed key to Ptomoaphagus.

Getting it to genus wasn't the end of my troubles... I wasn't convinced the fore tarsi were quite as expanded as shown in the diagram (in Duff) for subvillosus. Duff also provides a ratio between the length and width of the fore tarsus so I measured it on my specimen. I am not sure if you're meant to include the claws when measuring tarsal length but if I did include the claws the ratio was over 3, and if I didn't include the claws the ratio was nearly 2.8. It's supposed to be about 2.5 for subvillosus and more than 3 for medius. Hackston provides an additional character - the shape of the hind tibia, straighter on medius. Mine seemed pretty straight - certainly closer to the diagram in Hackston for medius than for subvillous. But I don't think medius has been recorded in Norfolk so that seems pretty unlikely. The size of the beetle was in range for both species according to Duff, but too big for medius based on the size range given in Hackston. I needed to check the aedeagus and that clearly pointed away from medius - it was subvillosus.

male Ptomaphagus subvillosus showing back of head after partial removal, sternites, hind tarsus, fore tarsus, hind tibia and aedeagus (side and flat), North Elmham (Norfolk, UK), 2nd April 2024

I had collected this one from a pitfall trap (in propylene glycol, so no live photos) a couple of days earlier, though I didn't dig it out and ID it until after the one above. With that experience fresh in my memory it was a relatively straightforward ID. The proportions of the fore tarsi were more obviously correct. It was about 3.0mm long.

male Ptomaphagus subvillosus showing abdomen from below, back of head, elytral apex, pronotum, hind tarsus, fore tarsus and aedaegus (3 views), Wendling Beck Environment Project (Norfolk, UK), 29th to 31st March 2024

This one was in a pitfall trap in the same group as the one above. It was a bit larger, though as its head was unnaturally extended I wouldn't place too much weight on my measurement of 4.1mm. It was structurally different from the two above but given other similarities I suspected it would prove to be a female of the same species, and so it did. The spermatheca broke into two pieces but I managed to find both.

female Ptomaphagus subvillosus showing antenna, pronotum, hind tarsus, fore tarsus and spermatheca, Wendling Beck Environment Project (Norfolk, UK), 29th to 31st March 2024