Gymnopleurus sericatus Erichson, 1843, and its synonym G. modestus van Lansberge, 1886 (not Péringuey), are re-established as synonyms of G. humanus MacLeay, 1821, along with one further synonym, G. modestus Péringuey, 1888 (not van Lansberge) = G. peringueyi Shipp, 1895. G. humeralis Klug, 1855, is removed from synonymy with G. humanus MacLeay and reinstated as a valid species. G. humanus var. azureus Ferreira, 1954, is made a synonym of G. humeralis Klug. The confusion was apparently caused partly by unwitting redescriptions, partly by failure to note previous synonymies, and partly by failure to distinguish between a species centred in the arid southwest (G. humanus and its synonyms) and its larger-bodied, close relative from the mesic northeast of southern Africa (G. humeralis and its synonym). As the Kalahari forms a wide disjunction between the species' ranges, G. humanus (Karoo–Namib) and G. humeralis (dry savanna) may be differentiated by geographical location alone. The past practise of providing names for colour varieties is not considered useful as G. humanus shows the full range in exoskeleton colour variation, from entirely blue to entirely green to entirely cupreous, in the same local populations of the central Northern Cape, South Africa. Type specimens of G. humanus and its synonyms originated either from the southern range extremes (southern Karoo, South Africa) where the populations predominantly comprise blue individuals or from the northern extremes (southwest Angola) where the populations entirely comprise cupreous individuals.