Callicerus rigidicornis

This was collected from a pitfall trap (in propylene glycol, so no live photos). It seemed fairly distinctive though, as is so often the case with this family, I didn't find it easy to key. I eventually got it to genus using Mike Hackston's key and to species using the information at the UK Beetles website. It was about 3.8mm long.

Callicerus rigidicornis showing close-up of mandibles and palps and elytra, Wendling Beck Environment Project (Norfolk, UK), 29th to 31st March 2024

The one above was in a set of pitfall traps along a beetle bank. At the same time I had a set of pitfall traps in arable margin at the end of the same field and the next one was in one of those traps, about 425m away from the first. This one was about 3.7mm long.

Callicerus rigidicornis showing elytra, head, palps (from above and below) and antenna, Wendling Beck Environment Project (Norfolk, UK), 29th to 31st March 2024

This was in the same set of pitfall traps as the last and was slightly larger (measured at 4.1mm but it wasn't fully straightened out, so slightly longer). After the first one I'd got the impression that the palps were pretty much unique to this genus, but while I was examining this one I found some photos of another species of Aleocharinae in a different genus (assuming it had been correctly identified) which had fairly similar palps. So for this one I made sure I keyed it out using Hackton's keys really carefully, but again ended up at Callicerus.

Callicerus rigidicornis showing palps, Wendling Beck Environment Project (Norfolk, UK), 29th to 31st March 2024

By the time I found a fourth in the same set of traps I was beginning to question why I should be getting such a high abundance (5 in 18 traps left our for 48 hours) for a species that until 2021 had only been recorded 16 times in Norfolk. Am I identifying them correctly? If not I can't see where I'm going wrong, so unless someone can tell me otherwise I assume I'm right. Maybe it's because they're most active in spring before most coleopterists are setting pitfall traps? Or maybe it just happens to be a good site for them? This one was smaller, about 3.1mm long.

Callicerus rigidicornis showing antenna, palps and pronotal microsculpture, Wendling Beck Environment Project (Norfolk, UK), 29th to 31st March 2024

I couldn't get this one to lie striaght enough to measure it accurately but it was probably over 3.5mm long.

Callicerus rigidicornis showing palps, Wendling Beck Environment Project (Norfolk, UK), 29th to 31st March 2024