Bare-saddled Blood Bee Sphecodes ephippius

Blood Bees are a tricky group to identify and I've certainly struggled with the few that I've found. The first challenge is usually to work out of the area between the rear ocelli and the hind margin of the head is "with numerous punctures" or "rough (often ridged), without distinct punctures". On both of the following bees the area immediately behind the ocelli was clearly punctured. This area was very narrow (just 1-2 punctures deep) and behind this is a contrastingly ridged area. But this ridged area is distinctly sloped downwards which you might reasonably interpret (at least I did initially, and I don't think it was unreasonable to do so) as being the start of the hind margin of the head. So I took the narrow area of punctures to indicate the "with numerous punctures" option, which then leads to a dead end. Presumably we are to take the hind margin of the head as being the top of the concave area at the very back of the head where the thorax joins it, in which case the majority of the area between this and the ocelli is ridged.

female Bare-saddled Blood Bee Sphecodes ephippius showing back of head, North Elmham (Norfolk, UK), 26th April 2020

I had the same problem with interpreting the back of the head on this individual, but taking the punctured option didn't work. The hind tibia had reddish bristles surrounded by whitish hairs which would have made this Box-headed Blood Bee Sphecodes monilicornis, but try as I did I really couldn't make the head box-shaped, and with a forewing length of 4.6mm it was too small for monilicornis. It was only at this point that I remembered my previous problems with the back of the head, and corrected myself. Once that was sorted, getting it to ephippius was relatively straightforward.

female Bare-saddled Blood Bee Sphecodes ephippius showing hind tibia, back of head and scutum, North Elmham Cathedral Meadows (Norfolk, UK), 19th April 2021