Helophorus minutus

Helophorus minutus

This is apparently the commonest species of Helophorus in Norfolk but as it was the third of three Helophorus I examined from the same trap, I imagined it would be the same as the first two (brevipalpis) which was also the only species I'd identified previously. Taking it through the key (Duff) it quickly became clear that, unlike the brevipalpis, it was one of the species where the apical segment of the maxillary palps is not symmetrical.

Some of the judgements needed to finish keying it were a bit unclear, particularly when I got to the choice between minutus and griseus. At this point I tried Hackston's key, and this also seemed to arrive at minutus, or possibly griseus. I found it really hard to judge the shape of the pronotum - the slightest change of angle and it changed from rounded to straight or vice versa. I thought the other characters fitted minutus better but it was all a bit too marginal and/or subjective for my liking. Finally I checked the genitalia, but even that wasn't simple. There are differences between the two diagrams in Duff, and between the two diagrams in Hackston, and between the two photos at coleonet.de, but the differences between species were not consistent across the three sources so it was tricky to work out which ones were significant. In the end I felt it matched minutus best on all characters and in combination I think that makes for a safe ID (though as always, happy to hear if you disagree).

male Helophorus minutus showing pronotum and base of elytra (2 angles), close-up of pronotum (2 focuses, one with the disc in focus and the other with the side margins in focus), maxillary palps from side (both palps), frons, underside and aedeagus (2 photos, one with size scale), Wendling Beck Environment Project (Norfolk, UK), 14th July 2023

My next proved quite tricky and, being a female, the genitalia were no help. One apical maxillary palpomere looked more symmetrical like on brevipalpis but the other was clearly asymmetrical as on minutus etc. I wassn't convinced that the pronotum shape wasn't better for griseus than minutus, but in the end I think it must have been minutus. This one had a clearer yellow front and side border to the pronotum than the one above and, unlike most griseus, the marginal grooves of the pronotum were not blackened. Looking at the specimen, the contrast between the pale elytra and dark pronotum was as shown in the third photo below, not the two live photos where the elytra seem to be darker.