Black Headed Cardinal Beetle 

Photos by Mark Beaumont

The large size and bright colour is distinctive among British fauna; 14-20mm.

 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.