Nicrophorus humator (Gleditsch, 1767)
Black Sexton Beetle
This is generally one of our most common species of Nicrophorus, it occurs throughout mainland UK to the far north of Scotland and all the islands including Orkney and Shetland. On the continent it is similarly common from North Africa to Southern Scandinavia and east through Siberia to China and Japan. Adults occur from March until October and are strongly attracted to decaying organic matter, especially carrion and decaying fungi but might also occur in other situations, they fly to host material at night and are often common at light or in flight-interception traps. Adults will often be found carrying phoretic mites ( Gamasidae, especially Gamasus crassipes L.) which are not parasitic but leave the beetle and enter host material where they kill off eggs and small larvae of diptera etc. which would otherwise compete with the beetle for food. They will arrive at any carrion, being attracted by smell over large distances, and are often present in numbers in baited traps but small carrion is preferred, rodents, birds and frogs etc., larger items may be dismembered in order to produce a mass that can be buried and several adults may do this but ultimately only one pair will bury it, they will fight over it until all but a single pair are driven off. When the carrion is suitably prepared and any fur or feathers are removed they will excavate the soil from underneath and slowly bury it, generally to a depth of 5 or 6 cm. but often deeper, and once buried they will form it into a condensed putrid ball and coat it with a secretion that will slow down the decay process. Once the food is prepared the female will excavate a short brood gallery where she will deposit eggs and there is evidence that she can regulate the number of eggs laid according to the amount of food available, in any case she will often kill larvae if they are too abundant. The larvae emerge quickly, within 12-48 hours, and enter the food via a small depression made by the female, now the female (known as a trophobiont-food provider) will feed the first instars with small prepared pellets of food until they moult. From the start of the second instar stage the larvae are able to feed themselves and they grow rapidly, passing through a third instar stage becoming fully grown within a week or two when they will enter adjacent soil and pupate. Adults emerge after about a week; they are white when freshly eclosed but remain in the soil for up to a week to harden and become pigmented.
18-26mm although larger specimens occasionally occur. Entirely black but for the elytral epipleura and antennal clubs which are red. Broad, elongate, flattened and heavily sclerotized for a fossorial lifestyle. Head with large convex eyes continuous with rounded temples strongly contracted to the base, vertex with longitudinal impressions beside the eyes and a transverse impression at the centre, clypeus finely transversely rugose. Antennae 11-segmented; scape long and curved, segments 2-5 narrow and 6-11 form a wide and abrupt club, black with the last three segments red. Pronotum transverse and irregularly rounded, disc convex and finely punctured and rugose, margins flat and more strongly punctured. Scutellum large and rounded apically, surface rugose and punctured in the basal half, smooth and punctured towards the apex. Elytra with indistinct shoulders and broadened towards the apex, apical margin truncate and sinuate leaving the last three abdominal tergites exposed. Lateral margins densely pubescent around the shoulders and the posterior angles, surface moderately strongly and densely punctured throughout, each with two distinct longitudinal carinae which are evanescent towards the base and apex and sometimes another indistinct lateral carina. Epipleura variable but usually to some extent red; often entirely so but generally at least around the middle. Legs long and very robust; tibiae gradually broadened to the apices and with long and stout apical spurs, meso- and metatarsal segments abruptly broadened before the apex, basal segments of protarsi widely lobed; much more strongly so in the male.