Badister collaris

A member of the subgenus Baudia, together with Badister dilatatus and Badister peltatus - the three species are very similar.

I initially thought my second sg. Baudia was sufficiently close in pronotum shape and aedeagus to a Badister dilatatus that I had previously identified to think it was another dilatatus. However, when I examined my third Baudia I thought the hind angle of the pronotum was too angled for dilatatus so it must be either peltatus or collaris. But it didn't seem all that different from this one which I thought I had confirmed as dilatatus by its genitalia, so I doubted it (it was female so I couldn't confirm it genitalically). Then I caught two more males which I thought must be peltatus or collaris on pronotum shape and confirmed both as collaris from their aedeagi. At that point I took a closer look at this second one which I had previously identified as dilatatus. Perhaps a bit subtle, but the pronotum shape was more angular than my original dilatatus, being more paralel-sided before the angle and straighter towards the neck behind the angle. I hadn't photographed the aedeagus flat (they're hard to hold still in flat position when in liquid), but from the not-quite-perfectly side view I thought I could see the notch at the apex. Moreover the subapical hook was straight out, unlike the dilatatus where it was downward pointing, smaller and sharper. The projection at the apex was also straighter and less blob-rounded at the tip. Surely this was also a collaris. This beetle was about 4.7mm long.

I don't have up-to-date information but until the end of 2021 there were only three records of collaris in Norfolk so I wonder if this is another of those beetles that is easier to find at light.

male Badister collaris showing close-up of pronotum, mandibles (3 views, 2 from in front and 1 from above), elytra tip and aedeagus, North Elmham (Norfolk, UK), 23rd June 2023

I believe this one is either peltatus or collaris but it was a female so there's no aedeagus to check. Hackston says that peltatus and collaris are more irridescent than dilatatus. The specimen doesn't look irridescent at all, but the live photos do. The specimen is about 5.0mm long.

female Badister peltatus or collaris showing mandibles and pronotum, North Elmham (Norfolk, UK), 21st June 2025

These are the two males that finally helped me resolve the first one above. Both came to light and looked distinctly irridescent. The first was 5.2mm long which is very slightly more than the top end of the range given by Duff. I had a slight wobble when keying these to genus as the claws seem to be very slightly toothed, or at least crenulate.

male Badister collaris showing hind claw, palps, mandibles, pronotum and aedeagus (side view and flat view of tip), Wendling Beck Environment Project (Norfolk, UK), 29th June 2025

second male Badister collaris showing pronotum and aedeagus (3 views), Wendling Beck Environment Project (Norfolk, UK), 29th June 2025