If you ask the man-in-the-street about beetles, he or his female equivalent tends to think of ‘black beetles’, i.e. cockroaches (Orthoptera) rather than real beetles (Coleoptera). Many beetles are of course black e.g. desert forms, which are black to absorb heat during cold nights, but many are very brightly coloured.

On 7th May 2007 I was with a group from the U3A in a small, damp, mixed wood by the River Lark at Fornham St Genieve (site of the Battle of Fornham, 1173) when we found several bright red Cardinal beetles, Pyrochroa serraticornis Scop., on nettles and rotting tree stumps. The upper surface of these magnificent beetles is bright red except for black antennae and palpi, and the legs and lower surface are black. All Cardinal beetles are rather flat and this one is about 12mm long. The base of the thorax is much narrower than the elytra at the shoulders and the antennae are pectinate (joints with projections suggesting a comb), especially those of the male. There is a similar but larger species (about 15mm) with a black head P. coccinea L. and very local in distribution, which I have found in Sussex. I do not know if it is recorded from Suffolk.

The adult beetle is usually found on flowers in June, but 2007 was an unusually ‘early’ year. The larvae live under the bark of fallen deciduous trees and are yellowish, long and flattened, with two ‘prongs’ at the tail end. They eat other insects or, if none are available, each other. So, why the colour, which is extremely obvious against the dark colour of the nettles? We can assume that this is a warning colouration and a look at some of the beetle’s relatives makes this very likely. The Oil beetle Meloe proscarabaeus L., which occurs in Suffolk, protects itself by giving out a foul-smelling liquid from its joints, but more famous is the Blister beetle or Spanish fly, which contains canthadarin, a powerful irritant. Beetles were once dried and sold as an aphrodisiac. Some of its other relatives, such as Oedemera spp. which are also found on flowers tend to be green and less obvious and may make better eating. Another hint that Cardinal beetles are unpleasant to eat is that they are weakly chitinised and have a relatively soft cuticle; less palatable beetles usually have a thick exoskeleton and are harder to crunch but in Pyrochroa the taste is a sufficient deterrent.

Are Cardinal beetles common everywhere this season? I have never seen them in large numbers before.