Pyrochroa coccinea (Linnaeus, 1761)

Black-headed Cardinal Beetle

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POLYPHAGA Emery, 1886

TENEBRIONOIDEA Latreille, 1802

PYROCHROIDAE Latreille, 1806

PYROCHROA Geoffroy, 1762

The European distribution is mainly central, extending south to the Pyrenees, central Italy and Greece; north to southern Scandinavia and the UK, and further east it occurs in Ukraine, western Russia and Kazakhstan. It is one of the more frequent members of the family and is locally common throughout its range; in the UK it is generally common in southeast England but more local and sporadic further north to the Lake District although it is generally absent from the West Country and Wales. Adults are short-lived and have a brief season, usually appearing in April, becoming common through May and early June and only rarely encountered later, they are diurnal and lead an exposed and conspicuous lifestyle on herbaceous vegetation, typically in wooded situations with a supply of decaying logs and fallen timber. Mating occurs early in the season and females oviposit among or beneath areas of dead bark on a range of broadleaf wood, more especially oak and beech, usually on fallen timber or more rarely on standing trunks, eggs are laid in small batches and larvae will develop in groups under bark feeding upon decaying bark, dead insects and their excrement and microorganisms living in among the detritus although at high densities they are known to become cannibalistic. Larvae develop over several years and in habitats where host material is abundant and the beetles become common there may be larvae of several generations present under a single area of bark; small larvae generally occur under close-fitting bark but as they grow and the bark loosens it becomes easy to find aggregations of large larvae under loose and detritus filled bark, this may explain why females generally oviposit on fallen timber where the bark will remain in place as it becomes loose. Larvae may be found throughout the year; when fully-grown they pupate under bark in the spring and adults eclose after a few weeks. Adults are predatory, feeding on a variety of small insects etc. among foliage or on flowers and they will also consume pollen, they emerge from beneath bark and become active during the first warm days of April; at first they remain about the host material and at this time may be found mating, later on they disperse by flight and might be found on herbage in any situation not too far from decaying wood, they often bask exposed to the sun and protected by their aposematic colouration. They are known to be toxic to predators, males can synthesize their own cantharidin and this is passed to the female during mating and then to the eggs during oviposition.

The large size and bright colour is distinctive among our fauna; 14-20mm. Pronotum and elytra vivid red or scarlet, otherwise rather shiny black. Certain lycids are superficially similar, and occur in similar habitats, but here the pronota and elytra are characteristically sculptured, unlike the smooth and soft cuticle of the pyrochroids. The lily beetle might also be casually mistaken for the present species as it is similar in overall colouration but, as well as being generally different in detail, it has distinct punctured striae to the elytra. Among the longhorns Pyrrhidium might also be a candidate for confusion but here the expanded femora, filiform antennae and pubescent elytra, among other things, are distinctive. The larvae are also distinct; creamy grey or yellow, very elongate and flattened with each thoracic and abdominal segment separately rounded, each thoracic segment bears a pair of short robust legs and the eighth tergite has a transverse raised line at the base, this is missing in the otherwise very similar larva of P. serraticornis. In both species the terminal abdominal segment bears a pair of well-sclerotized straight urogomphi. The sexes are readily separated; Antennae pectinate in male, serrate in female; male with deep depression between eyes, in female much shallower.

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