A family of just three species:
Common or Red-headed Cardinal Beetle Pyrochroa serraticornis
Black-headed Cardinal Beetle Pyrochroa coccinea
Scarce Cardinal Beetle Schizotus pectinicornis
The adults are spectacular large black-and-red beetles.
Schizotus pectinicornis is smaller (7 – 9 mm; compared to 12 – 19 mm for the Pyrochroa species) and as well as having a black head and scutellum, has a blackish spot in the middle of the pronotum (photo here). A key to the three species is provided in Buck’s (1954) RES Handbook.
All three are saproxylic species with long, flattened larvae that develop under bark of decaying wood. In fact, the larvae are easier to find, and findable over a longer season than the adults, and can usually be quite easily identified to species in the field.
A well-illustrated key to larvae was provided by van Emden (1943).
Buck, F.D. (1954). Coleoptera (Lagriidae, Alleculidae, Tetratomidae, Melandryidae, Salpingidae, Pythidae, Mycteridae, Oedemeridae, Mordellidae, Scraptiidae, Pyrochroidae, Rhipiphoridae, Anthicidae, Aderidae and Meloidae). Handbooks for the identification of British insects, vol. V, part 9. London: Royal Entomological Society. Out of print but available as a free download here.
van Emden, F.I. (1943). Larvae of British beetles. IV. Various small families. Entomologist’s monthly magazine, ?78?(1943), 209 – 223 and 259 – 270.