Genus Macroderes Westwood, 1842
Macroderes Westwood, 1842 is a small genus (15 species) of the scarabaeine dung beetles endemic to southern Africa. Species of Macroderes are of medium size and can be recognized by their convex, bulky body and absence of wings. Colour monotonous black; recently emerged specimens reddish-brown. Males have tibiae with acute process next to apical spur, similar to that of representatives of genera Xinidium Harold and Metacatharsius Paulian.
With the exception of M. foveatus and M. cornutus, which are readily distinguished by a prominent deep triangular concavity at base of pronotum, all other species of Macroderes are superficially similar but can in most cases be identified by the characters of microsculpture of pronotum and elytra. The shape of a small, usually strongly sclerotized sclerite of the internal sac of the aedeagus is species-specific. Allopatric habitats of most species provide an additional, geographic diagnostic character. Females sometimes cannot be identified with reliability when the locality they originate from is unknown.
Most of Macroderes species distributed in south-western part of South Africa from Richtersveld in the north to Cape Agulhas in the south. M. pristinus was described from "Diamond field" [present-day Diamond Area 1 in southern Namibia] which is the northernmost known locality of Macroderes species. This record is however ambiguous. The genus range largely falls into the winter-rainfall area. The notable exception is M. bias which occurs eastwards of ranges of other species up to Uniondale in the west. It can be assumed that most Macroderes species are allopatric except for M. minutus which has recently been collected along with specimens of M. amplior (in vicinity of Rietpoort) and M. arrowi (in vicinity of Vanrhynsdorp).
Distribution map of Macroderes
The biology of Macroderes is little known except for some recent observations in Namaqualand. It was noted that the beetles occur in shrub-land areas with rather dense vegetation. The soil types varied from loam in Kamieskroon and Rietpoort to soft sand in coastal area and vicinity of Vanrhynsdorp but is probably species-specific. Feeding of the beetles was not observed in the field nor were the beetles found on the soil surface in day-time. We suppose that the Macroderes species are nocturnal but, however, may be active in day-time in case of cold and humid weather. The Macroderes tolerate quite low temperatures since the temperature went as down as 4°C at nights in the survey period in central Namaqualand. In the laboratory at the University of Pretoria, beetles fed on cattle and sheep dung. They dug vertical burrows in soil and stayed there during light-time appearing at night to collect some food. The beetles carried pieces of dung with their anterior legs moving back to their burrows.
Frolov, A. V. & Scholtz, C. H. 2005. Revision of the southern African genus Macroderes Westwood (Coleoptera: Scarabaeidae: Scarabaeinae). Annales de la Société Entomologique de France (N. S.), 40(3-4): 371-391.
Janssens, A. 1939. Coprini. Exploration du Parc National Albert, Mission G.F. de Witte, 29: 1-104.
Preudhomme de Borre, A. 1880. Note sur le genre Macroderes Westwood. Annales de la Societe Entomologique de Belge, 23: 7-11.
Westwood, J. O. 1842. Descriptions of some new exotic genera belonging to the family of the sacred beetles. In: Proceedings of the Royal entomological Society of London, pp. 58-59.