Necrobia violacea (Linnaeus, 1758)
POLYPHAGA Emery, 1886
CLEROIDEA Latreille, 1802
KORYNETINAE Laporte, 1836
Necrobia Olivier, 1795
Native to the Palaearctic region where it very widespread and locally common from Europe to the far east of Russia and China, it has been widely transported over the centuries along with food stuffs etc. and is now more-or-less cosmopolitan in distribution; it occurs throughout Europe to the far north of Fennoscandia and the UK and occurs both in the wild and under artificial conditions. In North America it has long been considered as an introduction from Europe; it has been known since the 19th century and is now widespread but recent find from the La Brea Tar Pits in California dated at about 44,000 years old suggest an ancient Holarctic distribution. In the UK it is very local in England, Wales and Southern Scotland and there are scattered records from Ireland, adults are active over a long season in the wild and may be found in most fairly dry habitats among old and dry carrion or bones or on flowers in warm sunshine. Both adults and larvae are saprophagous and predaceous, they feed on dry organic detritus and actively predate diptera larvae and other insects associated with this environment but may also occur in other situations e.g. in Europe the larvae have been recorded from Hylotrupes galleries. Mating occurs throughout the season, females oviposit among likely host material and fresh adults occur in late summer and autumn and are thought to overwinter. Under artificial conditions both stages occur among decaying foods of animal origin infested with insect eggs and larvae, and adults have been observed to predate dermestid and other larvae although they have also been reared from dead rats devoid of other insects. Larvae and adults have been observed devouring fly pupae from within, and both active and quiescent larvae as well as pupae have been found within fly pupae, the entrance hole sealed by the larva with a white secretion. Adults may be sampled by searching through or pitfall trapping among any dry carrion or bones in almost any situation e.g. they have been recorded from old cattle bones on open pasture and dry decaying fish in reed beds, they may also occur while sweeping flowers or vegetation in warm weather, they fly well and are attracted to carrion over long distances but generally occur in small numbers.
Necrobia violacea 1
Necrobia violacea 2
4-5mm. Elongate and discontinuous in outline, body and legs metallic dark blue, antennae black, dorsal surface with long and erect dark pubescence. Head transverse with large convex eyes and narrow palps, antennae with an abrupt, broad and compact club with segments 9 and 10 widely transverse. Pronotum transverse, broadest below the middle and rounded to obtuse anterior and posterior angles, lateral margins bordered and often appearing crenulate towards the base, surface densely and discretely punctured throughout. Elytra broader across the base than the broadest part of the pronotum, with rounded shoulders and slightly dilated toward a continuous apical margin, striae strongly punctured and distinct into the apical third or so, interstices uneven and finely punctured throughout. Legs short ad robust, femora simple, tibiae with very fine, hardly noticeable, apical spurs, and tarsi appearing 4-segmented, the tiny fourth segment almost completely hidden by the widely-bilobed third segment. All claws with a strong basal tooth.
Among our UK fauna only likely to be confused with Korynetes caeruleus but here the antennal club is narrower and longer, the head is proportionally broader and the elytral striae are less strongly punctured.