Necrobia rufipes (De Geer, 1775)
POLYPHAGA Emery, 1886
CLEROIDEA Latreille, 1802
KORYNETINAE Laporte, 1836
Necrobia Olivier, 1795
Formerly a serious pest of stored products in temperate regions but now much less frequent due to modern hygiene measures, this species is native to the Palaearctic region but is now more-or-less cosmopolitan in distribution, it remains abundant and is among the most damaging of pests in many warmer parts of the world and while it is in some sense beneficial as both adults and larvae prey on other pest species this is far offset by the damage it causes. In northern temperate regions it is almost exclusively synanthropic although there are records of adults from the wild during the summer and even overwintering, and larger larvae have been found to survive moderate winters outside and go on to pupate when the temperature increased in the spring. The species is regularly imported to Europe with foods etc. from warmer regions and there are records going back centuries from most countries including the UK, adults can occur in the wild during the warmer months but they occur year-round and may be continuously breeding under artificial conditions. All stages typically occur among dried and stored foods of all kinds as well as in carrion, guano, animal skins and even museum specimens. Adults and larvae typically seek out and consume other pests within the host material and they are often cannibalistic but while searching for prey they will consume any protein-rich organic material, especially dried and fresh meats, they are often found among stored cheese, nuts and oil seeds and in the tropics they are sometimes referred to as copra beetles as they may be especially common among dried coconuts. The life cycle duration depends on temperature, humidity and nutrition and varies between one and six months, and adults have been recorded living for almost a year. Adults feed and mate soon after emerging and females oviposit for up to three months, producing between 100 and 3000 eggs depending upon temperature etc., they lay small numbers of eggs in crevices close to host material, probably to reduce cannibalism, and larvae emerge within a week or so and consume the surrounding eggs before moving into the host material. Larvae pass through three or four instars over a one to four month period and when fully-grown wander off to find a secluded spot away from the host material to construct a cocoon and pupate. Adults eclose after a week or so and begin feeding immediately. Adults fly well and readily disperse to nearby host material, they are primarily predaceous but will tunnel into any suitable material, consuming it as they search for prey, and in this way they can cause serious damage to museum specimens etc., the larvae likewise bore into host material when small and so the only evidence of their presence are inconspicuous holes on the surface, but large cheeses and hams may become alive inside with growing larvae. A serious infestation under good conditions and with an unlimited food source can increase in numbers by a factor of 25 per month and so large food stores can soon become worthless as the populations of other pests are consumed and the beetles begin to consume the host material. Infestations are now rare in the UK, they still occur but are usually easy to detect through monitoring as the adults are very distinctive and often occur outside the host material as they disperse.
Necrobia rufipes 1
Necrobia rufipes 2
4-6mm. Elongate and moderately convex, easily identified by the overall appearance and the colour; entirely shiny metallic blue (although there is a rare form with coppery elytra), legs, mouthparts and basal antennal segments red and the entire dorsal surface with fine erect dark pubescence. Head transverse with large convex eyes that occupy almost the entire lateral margin, vertex evenly convex and sparsely punctured. Antennae inserted laterally in front of the eyes, 11-segmented with an abrupt 3-segmented club, segments 1-6 pale red, 7 and 8 9-11 black. Pronotum evenly rounded laterally to widely obtuse angles, anterior and basal margins weakly curved, surface evenly convex and finely and closely punctured, usually a little more densely so than the head. Elytra broader across the base than the width of the pronotum, elongate and evenly rounded behind the middle to a continuously-curved apical margin, surface rugose and finely punctured between punctured striae that become weaker beyond the middle. Legs entirely red although the coxae are usually much darker, femora and tibiae smooth and with only short and very fine apical spurs, tarsi 5-segmented with segment three distinctly bilobed and segment two a little more weakly so.