Geotrupes spiniger (Marsham, 1802)

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POLYPHAGA Emery, 1886

SCARABAEOIDEA Latreille, 1802

GEOTRUPIDAE Latreille, 1802

GEOTRUPINAE Latreille, 1802

GEOTRUPES Latreille, 1797

This species is generally common from lowlands to low mountain altitudes across southern and central Europe reaching north to the UK and southern Fennoscandia, to the east it occurs from Iran through Asia Minor and Russia to western Asia, and here it is locally common throughout the south of England and Wales, becoming less so further north and almost absent from the West Country. In Scotland there are a few scattered records from the highlands and the Western Isles. Despite a recent decline it remains one of our most common geotrupids, occurring on cattle pasture and among horse dung in a wide range of situations including woodland, moorland and dunes.  Adults appear early in the year and may remain active into October, they are usually crepuscular or nocturnal but on warm days may be seen in the open, usually upon dung or among surrounding short grass, they fly well and are often attracted in numbers to light or freshly-deposited dung. Mating occurs in the spring and early summer and the female will then excavate a vertical burrow directly beneath a dung pat, from this central burrow she then excavates horizontal branches and provisions each with a cylindrical brood mass of dung, generally about 100mm long and 25mm across, into which she will lay a single egg. Working up the central burrow she will use soil from each brood chamber to cap the previous one and, once filled in, she will display avoidance behaviour towards the buried dung.  Larvae develop during the summer and either pupate in the burrows during the autumn, in which case the adults will eclose and may feed for a while before overwintering within the burrow, or overwinter and pupate in the spring to produce adults a little later than those that overwintered. This is one of the species to be found in flight over dung pasture on warm spring and early summer evenings, and by late spring many, if not most, will be found carrying large numbers of phoretic mites beneath the thorax and abdomen. Specimens will need to be examined carefully at first because G. stercorarius (Linnaeus, 1758) is equally common and the two may occur together.

Among the U.K. fauna our geotrupids are distinctive, and with a little experience this elongate-oval species with well-impressed elytra striae will become obvious; the only confusion will be with G. stercorarius (Linnaeus, 1758) but here the abdominal punctures and pubescence are uniformly distributed. Among the largest of our species at 16-26mm, the upper surface is black, often with a faint metallic lustre and usually with blue margins to the pronotum and elytra, the overall habitus is very convex, distinctly elongate and parallel-sided, and it is generally a little less shining than stercorarius. The underside is entirely bright metallic blue although the legs may differ slightly in colour and contrast against the body.The pronotum often has a longitudinal punctured and impressed line medially towards the base, and the overall punctation is sparse, becoming a little denser towards the lateral margins.  Elytra with 7 well-impressed striae between the suture and the shoulder, the interstices either entirely smooth or cross rugose only towards the apex. The abdominal sternites are more strongly punctured and pubescent towards the lateral margins; the centre line being almost smooth and glabrous. The outer face of the hind tibiae has complete transverse raised lines joining the apical 3 pairs of teeth.

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