POLYPHAGA Emery, 1886
STAPHYLINOIDEA Latreille, 1802
SILPHIDAE Latreille, 1806
Large and distinctive species associated with carrion and a variety of decaying organic material. Several species are common and will soon be encountered in a range of habitats.
Around the World
Members of this family are often referred to as large carrion beetles to differentiate them from the many other smaller beetles to be found at carrion e.g. staphs, leiodids or histerids etc. Members range from 7 to 45mm. They occur throughout the world and number about 200 species in 15 genera and 2 subfamilies; Nicrophorinae Kirby, 1837 and Silphinae Kirby, 1837. The widest diversity occurs in the Palaearctic region and while there are species in the tropics of Australia and South America they are generally rare in tropical regions, probably due to severe competition from other carrion feeders. Members of the Nicrophorinae mostly occur in northern temperate regions while the Silphinae seem more tolerant of warmer regions and are correspondingly more widespread. With 12 genera the Silphinae are the more diverse while the Nicrophorinae contains only 3 genera dominated by the widespread genus Nicrophorus Fabricius, 1775 with about 70 species. About 46 species occur in the Nearctic region of which 30 species in 8 genera are recorded from the U.S.A. The U.K. fauna provides a good representation of the North West European fauna which includes 28 species; 11 Nicrophorinae and 17 Silphinae:
Nicrophorus Fabricius, 1775, 11 species.
Aclypea Reitter, 1884, 3 species.
Oiceoptoma Leach, 1815, 1 species.
Silpha Linnaeus, 1758, 8 species.
Thanatophilus Leach, 1815, 3 species.
Necrodes Leach, 1815, 1 species.
Dendroxena Motschulsky, 1858, 1 species.
Antennae widely separated and inserted on the lateral side of the head. In some species only the last 3 segments are finely pubescent but generally segments 8-11 and the basal segment are finely and evenly pubescent, the others have larger setae at the apex. Elongate, oblong or oval and very robust beetles, almost circular in form in the American species Necrophila americana (L.) Many, or most, are are flat or flattened dorsally at least. Most are dark coloured and many display aposematic colouration or a distinct
pattern e.g. Nicrophorus, Oiceoptoma or Dendroxena. The pronotum is variously shaped and generally large; usually quadrate to transverse, parallel to strongly narrowed anteriorly, rounded in the front half or with distinct front angles. The surface sculpture is very variable with ridges, fovea and extensive deep depressions. In some the pronotum is smooth. The scutellum is prominent and usually very large; sometimes as wide and/or as long as the head. The elytra are sometimes truncate (Nicrophorus, Necrodes) exposing 3 or 4 strongly sclerotized segments. In other genera they are entire, usually flattened, often ridged and variously punctured and pubescent. They are often widely explanate laterally and evenly rounded apically. Abdomen with 6 or 7 visible sternites; the second (first visible) only visible laterally of the metacoxae. Legs robust; tibiae usually with external apical spurs (except in Necrodes); well developed on the front legs. Tarsi always 5-5-5. The two subfamilies are very well differentiated so that a familiarity with Nicrophorus will serve to place all the species in the appropriate group.
SILPHINAE Latreille, 1806
Generally dark species but some are bicoloured or patterned. 8-25mm Oval and flattened species. Elytra generally carinate, sometimes smooth but never striate. Generally glabrous; only occasionally pubescent. Frontoclypeal suture absent or very weak. Gular sutures separate but becoming proximal at the centre. Antennae 11-segmented; gradually widened or with a weak and loose club. Many species are associated with carrion where they live and breed and upon which the larvae will develop, but other food sources are utilized; decaying fungi, compost and dung will sometimes produce species. Some species actively hunt for other insects and their larvae among foliage while others are phytophages. Some have been notorious pests of crops e.g. Aclypea on the continent or Necrophila in the U.S.A. feeding on pumpkins, spinach and beet crops. Many species consume larvae and other organisms present in carrion and decaying fungi etc. and some are adapted, with the head elongated, to feed on pulmonate snails. Most species are nocturnal. As with the Nicrophorinae, development is rapid; larvae develop in 6-8 weeks and the pupal stage lasts for 2 or 3 weeks, although not so rapid as in that group, and there is a single generation each year. The species show little or no parental care. Many are fully winged but flightless. The larvae are campodeiform, dark and strongly sclerotized, and usually shiny. 12-40mm. Head with 6 pigmented ocelli on each side. The tergites are large and transverse and usually with the hind angles produced. The anal lobes have many fine teeth. Overall the larvae are reminiscent of large and dark woodlice.
NICROPHORINAE Kirby, 1837
Species of this subfamily are very distinctive and a familiarity with the British species will serve to place all the members with confidence. The genus Nicrophorus contains about seventy species with a worldwide distribution but the most diverse regions are the Palaearctic and Oriental. They are among the largest and most conspicuous of the staphylinoid beetles. 12-30mm. Head relatively large with prominent eyes and characteristic antennae (see above). Frontoclypeal suture obvious as a transverse impression between the anterior margins of the eyes. Pronotum almost quadrate and usually deeply impressed behind the anterior and posterior margins. Variously pubescent or glabrous. Elytra truncate and often, or usually, with transverse red fascia which generally extend to the epipleurae. Usually almost entirely glabrous and with several longitudinal ridges but without striae. Three or four heavily sclerotized abdominal segments are visible beyond the elytral apex. In most species the male protarsomeres are dilated. The larvae are broadly campodeiform; the integument is pale and lightly sclerotized, except for the head and the legs, and the underside is white or creamy white. There is only a single, unpigmented, ocellus on each side of the head. The abdominal tergites are transverse, each with four small spines, and the anal lobes lack teeth.
Nicrophorus species are unusual among beetles as they display biparental care of the larvae. They feed and breed on carrion and some species will breed communally on carrion too large to bury. Most species breed at small carcases of rodents and birds. Usually being attracted by the smell, a carcass will attract many individuals and the beetles will fight; males with males and females likewise, for the right to bury and breed on the food source. If a single male arrives at carrion it will wait for a partner to arrive; they attract females by releasing a pheromone from the tip of the abdomen. Females can bury a carcass and raise larvae alone from sperm stored from previous matings. The pair digs a depression beneath the carcass by pushing soil forward with their heads, if the soil is too hard they will move the carcass a short distance to more suitable substrate. Before burying the carcass they remove the fur or feathers and smear it with bactericide and fungicide to slow the decay and make it less attractive to other beetles and flies etc. Before burial the carcass is rolled into a ball. The removed fur etc. is used to line and reinforce the burial chamber, and the complete process of burial may take eight hours. Eggs are laid in the soil and the newly hatched larvae move onto the carcass. Adults feed on the carrion and regurgitate liquid food in response to begging behaviour from the larvae, this is thought to speed larval development and also to help preserve the food. If there are too many larvae the adults will selectively cull them at an early age. Adults protect and provision the larvae throughout their lives, eliminating competition from dipteral larvae etc. Full grown larvae move into the soil to pupate. Adults are most active at night and will sometimes come to light; they occur regularly at m.v. traps used to survey moths. They are often observed to be carrying phoretic mites, in some cases being covered in them, and this is a mutualistic relationship; arriving at a carcass the young mites leave the beetle and start feeding on fly eggs and small larvae thus helping to eliminate competition for the food. Development, depending to some extent on the food source, is usually rapid; eggs hatch within 12-48 hours of being laid, larvae take a week or two to develop and the pupal stage takes 6-8 days to complete. For the purpose of recording these beetles they are readily attracted to carrion traps and may be found in decaying fungi, both terrestrial and arboreal, and sometimes in decaying vegetation and even dung.
A key to the British species of Silphidae can be found HERE.
SILPHINAE - Carrion Beetles
NICROPHORINAE - Sexton Beetles
Beetles of Britain and Ireland vol. 1
Andrew G. Duff
Provides keys and accounts on all the UK species.
Includes a key to all UK species.