Brachyarthrum limitatum

I was unable to find an ID for this by picture-matching against the British Bugs website which is usually a good first step when faced with an unfamiliar bug, as currently they only have photos of females for this species which looks rather different. Using ObsIdentify was equally inadequate, with Orthonotus rufifrons initially being suggested (with high degree of confidence on one occasion). Google Lens did suggest Brachyarthrum limitatum but when I reviewed online photos labelled as both species at, for example, GBIF, I found photos of both species that looked extremely similar to my specimen.

Most photos of male Orthonotus rufifrons showed a number of differences from my specimen, but a couple (including this one which happened to be one of the first ones I looked at) were extremely similar and, if they were labelled correctly, I couldn't tell what the difference the two species was. The draft key by Nau didn't really help as these two species diverge at a couplet which gives "A1 with at least a black mark on outer face & A2 with at least a black ring at base" for Orthonotus rufifrons (among other things) and "Antenna not as above" for Brachyarthrum limitatum (and others), however photos of males of both species appear to show essentially the same black A1 and A2. The key gives a size of 4.6mm for Brachyarthrum limitatum and 4.3mm for Orthonotus rufifrons - my specimen was 4.6mm but these two lengths are too close - I can't rule out the latter based on a difference of 0.3mm. There was nothing else in the key progressing to either species that ruled out either option.

After closely examining a range of other photos of both species I eventually concluded that the two photos of Orthonotus rufifrons that resembled my specimen were probably in fact misidentified Brachyarthrum limitatum (and I wonder if these were among the images ObsID's training was based on). Every other photo of Orthonotus rufifrons differed from Brachyarthrum limitatum in a number of ways, most obviously that on Orthonotus rufifrons's antenna there is a strong contrast between the black second segment and the pale third and fourth, whereas on Brachyarthrum limitatum the third segment is much darker, only slightly paler than the second. Other differences included the weaker colour of the legs (though variable and possibly overlapping), greater extent of pale on the cuneus, less orange on the cuneus especially at the base and no orange spots at the base of the wings.

male Brachyarthrum limitatum showing rostrum, hind tibial spurs, pronotum, hairs on clavus and corium and right clasper from below, North Elmham (Norfolk, UK), 6th June 2026