In a recent taxonomic revision of this genus Cuezzo (2000) recognizes three species from the Nearctic region: F. mccooki (McCook 1880), F. pruinosus (Roger 1863a) and F. analis ( André 1893b), with the last-named being removed from synonymy under F. pruinosus . All three species are recorded by Cuezzo (2000) from California. F. mccooki can be recognized by its abundant standing pilosity, but F. pruinosus and F. analis cannot be reliably distinguished using the differences cited by Cuezzo (2000). In Cuezzo’s worker key F. analis is separated from F. pruinosus based on the shape of the posterior margin of the head: concave (“sometimes…weak”) in F. analis , and straight in F. pruinosus . Yet, this putative difference is contradicted by Cuezzo’s description of the F. analis worker -where the posterior margin is said to vary from convex to weakly concave -and by the illustration of a F. analis worker (Cuezzo 2000, figure 10) which shows a posterior margin that is convex. ( F. pruinosus is described, and illustrated, as having the posterior margin of the head straight.) After examining a large series of Forelius from the United States and northern Mexico I can find no consistent difference in worker head shape: the posterior margin of the head varies continuously from weakly convex through straight to weakly concave. Color is also variable, ranging from dark brown to yellowish-orange. Some nest series contain both light and dark-colored workers. It is possible that the California populations are not conspecific with F. pruinosus (described from Cuba), but these and other western samples seem to grade insensibly into material from farther east and south, including populations in Florida and the West Indies with consistently dark and densely pubescent workers, which correspond to F. pruinosus (s.s.). The complex needs further study but because reliable diagnostic differences have not yet been uncovered I treat F. analis (type locality Chihuahua, Mexico) as a junior synonym of F. pruinosus ( syn. nov. ), thus returning to the conventional treatment of these two names.
It should be noted that even the distinction between F. mccooki (standing hairs present on scapes, posterior margin of head, and external face of tibiae) and F. pruinosus (standing hairs absent or very sparse on the afore-mentioned structures) occasionally breaks down in western North America, with workers from some localities showing intermediate amounts of pilosity. There is, however, a third distinct (and apparently undescribed) species of Forelius in the United States. It is small and dark with a conspicuously shiny mesepisternum, short scapes (SL 0.40-0.48), and sparse standing pilosity. This species ranges from southern Texas to Colombia, and has been found sympatrically with a larger Forelius species -apparently F. pruinosus -in Mexico, Guatemala and Costa Rica, without showing any sign of intergradation.
As a nomenclatural side note, the author of Forelius mccooki is McCook not Forel, since McCook’s 1880 paper provides in his own words a sufficient “description or definition ” (ICZN, Article 12) of the ants to make the name available, prior to Forel’s (1886b) more detailed description of the same material. In addition, the date of publication of McCook’s paper is 1880 (Ward et al. 1996: 275), not 1879 as cited by Bolton (1995b) and others. Cuezzo’s (2000) attribution of authorship of F. mccooki to Forel is incorrect, but her designation of a lectotype from among material in the Forel collection in MHNG may be considered justifiable, to the extent that Forel’s specimens came from McCook and were part of the material to which McCook referred in his 1880 paper.