Monomorium Mayr

Ward, P. S., 2005, A synoptic review of the ants of California (Hymenoptera: Formicidae), Zootaxa 936, pp. 1-68 : 14

Genus Monomorium Mayr

Leaving aside introduced species, the Nearctic Monomorium belong to the taxonomically vexing minimum ­group, revised by DuBois in 1986. Several of the species recognized by DuBois (1986) are problematic, and parts of his keys to workers and queens are unusable. Here I deal only with the two taxa recorded from California: M. wheelerorum DuBois is considered to be a junior synomym of M. ergatogyna Wheeler (syn. nov.) because the putative differences between the two “species” cannot be verified. A key distinguishing feature is said to be the lateral profile of the scutum and scutellum of the queen: flat or slightly depressed in M. wheelerorum and convex in M. ergatogyna . In populations from northern California, however, this character shows continuous variation between these two conditions, even among queens from the same nest (the species is polygynous). Other supposed queen and worker differences disappear when intra­ and interpopulation variation are taken into account. A modern systematic treatment of the M. minimum ­group is badly needed. Because the queens are apterous in most western populations, interpopulation differentiation is expected to be accentuated, a factor that needs to be considered in any taxonomic study.