Based on the original description and figures (Mackay and Mackay 2018: 111–113), the holotype of Camponotus cavibregma appears to be simply a queen of Ca. yogi. Its supposedly distinctive feature—a concave genal area, free of the short spatulate hairs that are common on surrounding anterior regions of the head—is observed also in queens of Ca. yogi (Fig. 5D). The description and illustrations of the paratype minor worker of Ca. cavibregma (Mackay and Mackay 2018: 109–111) similarly place it within the range of variation exhibited by minor workers of Ca. yogi.

Camponotus apostemata, described from a series of workers collected in northern Baja California (specimens from this series examined in LACM), is scarcely distinguishable from Camponotus yogi, and is here treated as part of the geographical variation of the latter species. The head of the major worker is a bit more strongly truncate than in populations farther north, but no consistent differences are seen in the minor workers. Johnson & Ward (2002) referred to these and other samples of Ca. yogi from Baja California as Camponotus sp. cf. yogi.

Camponotus yogi is closely related to Ca. clarithorax Creighton. The major worker of the latter species lacks a pitted, obliquely truncate head, but is otherwise structurally similar. The two species can be distinguished by differences in scape and leg length, with Ca. yogi having consistently shorter appendages than Ca. clarithorax (Fig. 6), although very small workers may be difficult to distinguish. The median clypeal notch or concavity is better developed, on average, in Ca. clarithorax workers than in those of Ca. yogi, a feature which led to the placement of Ca. clarithorax in the subgenus Myrmentoma, but neither species belongs in that subgenus. They are here treated as Camponotus (Camponotus) since genetic data indicate a fairly close relationship to other species in that subgenus (Wernegreen et al. 2009; Ward, unpublished). In addition to Ca. clarithorax and Ca. yogi, there are two other species in the Ca. yogi group: Ca. keiferi Wheeler, endemic to Isla Guadalupe, Mexico (and already placed in the nominate subgenus), and an undescribed species from the California Channel Islands (Ward, unpublished).

Figure 6. 

Plot of scape length (SL) against head width (HW) for workers of Camponotus clarithorax (n = 12) and Camponotus yogi (n = 27). Samples of Camponotus yogi from northern Baja California (BC) fall within the same cluster of points as those from California (CA).

Camponotus yogi is endemic to California and northern Baja California, where it occurs in coastal sage scrub, chaparral, oak woodland, and oak-juniper woodland. Nests are located in dead branches or stumps of various plants, always near the ground and often extending into live plant tissue. Creighton & Snelling (1967) reported this species nesting in live beetle-bored stems of Ericameria pinifolia, and tending pseudococcids in the stems.

Mackay (2019) discovered that the types of this species in BMNH—a syntype dealate queen and syntype major worker, the latter designated by him as lectotype—do not correspond to the species that has come to be known in the literature as Camponotus laevigatus. That species, given the new name Ca. laevissimus Mackay, is easily recognized by its shiny, iridescent blue-black integument and abundant and bright white standing pilosity on most of the body, including the scapes and tibiae (Fig. 7E, F). The real Camponotus laevigatus is a shiny black species, with relatively sparse standing pilosity, inconspicuous pubescence, slender scape base, and ecarinate clypeus. Examination of the lectotype image (Fig. 7A, B) shows that Camponotus laevigatus is conspecific with Ca. quercicola, a widespread California species that nests in the trunks and branches of oak trees (Gadau et al. 1999) (Fig. 7C, D). Mackay (2019) claimed that Ca. laevigatus differs from Ca. quercicola in having reduced pilosity on the head, but the lectotype is an old specimen in which the hairs are evidently abraded. Note the asymmetry in presence of hairs on the two sides of the head in the AntWeb image (e.g., short setae present on the left malar region but not on the right side) (Fig. 7A). Moreover, the amount of standing pilosity shows considerable variation in workers of Ca. quercicola, including setation on the malar region (Smith 1954; Gadau et al. 1999). We have examined a large series of Camponotus quercicola from throughout California, and we find that the type of Ca. laevigatus falls easily within the range of variation exhibited by this species. Mackay (2019: 321) also stated that the male and queen of Ca. quercicola (now Ca. laevigatus) are unknown, but this is incorrect: they were described and illustrated by Gadau et al. (1999) and compared with related species.

Figure 7. 

Camponotus workers, full-face (dorsal) views of head (A, C, E) and lateral views of body (B, D, F); scale bars = 1.0 mm. A, B: Camponotus laevigatus, lectotype (CASENT0903603). C, D: Camponotus quercicola, paratype (MCZ-ENT00029334), image from MCZbase (Museum of Comparative Zoology, Harvard University, copyright President and Fellows of Harvard College). E, F: Camponotus laevissimus (CASENT0280010). Images A, B, E, F from AntWeb (www.antweb.org); photographer Will Ericson.

Ca. adustus was described by Viehmeyer (1916) as a subspecies of Ca. bellus Forel, but examination of the original descriptions, images of types, and more recent material indicates that these two are distinct species. Camponotus bellus (syntype major worker, Amboina, Indonesia (Biró) [MHNG]; examined via image on AntWeb: CASENT0910513) has a matte integument and more abundant standing pilosity on the mesosoma, including the pronotum (Fig. 8C, D). In contrast, the body of Ca. adustus is predominantly shiny and standing pilosity is sparse on the mesosoma, being restricted to a single pair of long setae on the mesonotum and one pair at the junction of the dorsal and declivitous faces of the propodeum (Fig. 8A, B). Moreover, the two taxa have been recorded co-occurring in Singapore and remaining distinct (Viehmeyer 1916).

In addition to the foregoing pilosity characteristics, the minor worker of Ca. adustus has striking anterior and posterior protuberances on the dorsal face of the propodeum, and both the dorsal and declivitous faces are notably concave in lateral view (Fig. 8B). Under this general morphotype, however, there is a bewildering diversity of color forms whose taxonomic status is unclear. One of these, Ca. leucodiscus Wheeler, has also been treated as a subspecies of Ca. bellus, and is here raised to species (below), but its relationship to Ca. adustus remains to be clarified. The New Guinea species Camponotus weismanni Forel (syntype worker, Bismarck Archipelago; examined via image on AntWeb: FOCOL2297) might be a senior synonym of Ca. adustus, but the worker propodeum has less well-developed protuberances and a correspondingly less concave dorsal surface in profile.

Figure 8. 

Camponotus workers, full-face (dorsal) views of head (A, C) and lateral views of body (D, E); scale bars 0.5 mm. A, B: Camponotus adustus, holotype worker (FOCOL2281); scale bars = 0.5 mm. C, D: Camponotus bellus, syntype major worker (CASENT0910513). Images from AntWeb (www.antweb.org); photographers Christiana Klingenberg (A, B), and Zach (Ziv) Lieberman (C, D).

Workers associated with Ca. leucodiscus (i.e., matching the striking black and white color pattern on the gaster of the holotype queen) lack the matte integument and pilosity of Ca. bellus, and are instead shiny and with sparse pilosity, as described above for Ca. adustus. They apparently differ from workers of Ca. adustus by the longer, lower petiole and by the color pattern on the gaster. Both taxa that are here elevated to species are part of a larger assemblage of ants in the Ca. reticulatus group that need comprehensive taxonomic study.

Figure 9. 

Camponotus leucodiscus, lateral view of body; scale bar for A = 1.0 mm, no scale available for B. A: Holotype dealate queen (MCZ-ENT00021564), image from MCZbase (Museum of Comparative Zoology, Harvard University, copyright President and Fellows of Harvard College). B: worker, image from AntWiki (https://www.antwiki.org/wiki/File:Camponotus-bellus-leucodisc.jpg by Gary Alpert; used with Creative Commons CC 4.0).

Camponotini are well-defined morphologically based on the female castes (Bolton 2003). Males are identifiable as Formicinae by their long scapes, the strongly oblique gonocoxal-gonostylar articulation, absence of constriction between the third and fourth abdominal segments, and failure of the clypeus to extend between the antennal toruli, among other features (see subfamily key in Boudinot 2015). Given the available sample, male Camponotini are distinguishable from those of other formicine tribes by the following combination of traits (Fig. 10): (1) antennal toruli posteriorly-situated (i.e., anterior margins of torular rims distant from posterior clypeal margin); (2) antennae 13-merous; (3) arolia grossly enlarged; (4) gonostyli usually distinctly digitate (finger-like in shape and proportions); (5) waist simple, i.e., (5a) petiolar node usually vertical (except, e.g., Ca. (Myrmopytia) longicollis, which lacks a node altogether), (5b) petiole is not elongate posteriorly (e.g., anterior and posterior faces of node subequal in length), (5c) tergosternal articulation of abdominal segment III (AIII) is unfused, (5d) AIII articulation not raised dorsally above helcium, and (5e) the anterior surface of abdominal tergum III is convex, without a median longitudinal groove for reception of the petiole when “gaster” flexed anteriorly; (6) in most species, the first free abscissae of the radial sector and media veins (Rsf1 and Mf1) are characteristically aligned, forming a more-or-less straight line, although they may be kinked at the juncture of Rs+M, or have some other curvature; in rare cases, e.g., Colobopsis pylora (alate gyne examined), the abscissae meet at a distinct angle; (7) fore wing crossvein 1m-cu is usually absent (although loss within the group may have occurred in parallel, see Remarks below); and (8) head with distinct shape, resembling an inverted pear in full-face view: (8a) posterior head margin broadly convex, (8b) posterior head margin continuous or nearly so with the strongly bulging compound eyes (rarely the head is posteriorly elongate, e.g., Camponotus gouldi), (8c) malar area from the compound eyes to the mandibular insertion in full-face view strongly narrowed lateromedially, usually with parallel to subparallel malar margins that are almost orthogonal to the anterior eye margin.

Figure 10. 

Habitus of male Colobopsis and Camponotus; (A, B) heads in full-face (dorsal) view; (C, D) genitalia in dorsolateral oblique view; (E, F) bodies in profile view; (G, H) wings in ventral view; scale bars: A, B = 0.5 mm, C, D = 0.1 mm, E–G = 1.0 mm. A, C, E, G: Colobopsis species indet., from Fijian radiation (CASENT0171201). B, D, F, H: Camponotus planus (CASENT0173220, image from AntWeb [www.antweb.org], photographed by April Nobile). Abbreviations: atVIII = abdominal tergum VIII (metasomal VII), asIX = abdominal sternum IX (metasomal VIII), ce = cerci, gc = gonocoxa, gs = gonostylus, Mf1 = first free medial vein abscissa, psa = penial sclerite ventral apex, Rsf1 = first free radial sector vein abscissa, vo = volsella.

Calomyrmex Emery, Camponotus, Colobopsis, Dinomyrmex Ashmead, Echinopla F. Smith, Opisthopsis Dalla Torre, Overbeckia Viehmeyer, Polyrhachis F. Smith.

Camponotus and Colobopsis are globally distinguished from one another in the key to males provided below (section 3.3.2), and are the only camponotine genera occurring in the New World. In the Old World, these genera can be confused with Calomyrmex, Dinomyrmex, Echinopla, Opisthopsis, Overbeckia, or Polyrhachis, for which differentiating features are noted below. In general, Colobopsis is the only genus among these with antennal toruli situated at midlength of the frontal carinae, although some male Camponotus can be hard to evaluate due to poor development of the carinae. Further scrutiny of this condition is necessary.

Dinomyrmex males are readily identified by the following combination of states: (1) body massive, ~2 cm long; (2) head oddly shaped, with concave malar regions in full-face view; (3) propodeal spiracles long, slit-shaped; (4) petiolar node broadly wedge-shaped in profile view; (5) gonapophyses lateromedially flattened and weakly lobate; (6) golden pubescence present on pronotum; and (7) numerous long, reddish macrosetae present on pronotum, lateral mesonotum, and propodeum.

Polyrhachis is easily distinguished. Based on examination of a sample of males from nine of the 13 current valid Polyrhachis subgenera (Campomyrma Wheeler, Chariomyrma Forel, Cyrtomyrma Forel, Hagiomyrma Wheeler, Hemioptica Roger, Myrma Billberg, Myrmatopa Forel, Myrmhopla Forel, Polyrhachis), the following differential characters were observed for the genus: (1) head posteriorly truncate in posterior/posterodorsal view, with the posteromedian margin carinate; (2) frontal carinae usually robust, especially broad dorsoventrally dorsal to medial torular arch as seen in lateral view (orientation assuming prognathy), and often strong and well-marked; (3) third abdominal tergum often > 1/3 the total length of the gaster; and (4) helcial tergite elongate, with a very shallow notch or even an anteromedian lobe (e.g., in Polyrhachis sensu stricto), although the medial notch may be extremely long and narrow, reaching the helcial base, as in some Myrmatopa. None of the helcial states observed in Polyrhachis have been seen in Camponotus. While the genitalia and ninth abdominal sternum of Camponotus tend to be rather uniform, those of Polyrhachis vary considerably from species to species and subgenus to subgenus, in ways which are distinct from Camponotus and which deserve special attention.

The boundaries of Calomyrmex, Echinopla, Opisthopsis, and Overbeckia remain largely unexplored due to limited sampling. At least one species of Opisthopsis and one of Calomyrmex (in UCDC), and at least Colobopsis vitrea (male unknown) have the forewing crossvein 1m-cu enclosing and forming a discal cell. A discal cell is absent in Echinopla, Camponotus (including the recently demoted subgenus Phasmomyrmex), most Colobopsis, Overbeckia, and Polyrhachis. Opisthopsis (when 1m-cu present) and Calomyrmex (when 1m-cu present) may be distinguished from one another by the shape of the discal cell, being isosceles-shaped in Opisthopsis and subrectangular in Calomyrmex; however, this should be validated with a broader taxonomic sample. The examined male of Opisthopsis, that of O. haddoni (MHNG), was observed to have an exceptionally sharp and long ventroapical point of the penial sclerite; this species also has small ocelli, a very shallow and short posterior head margin posterad the compound eyes, and a large and convex anterior clypeal lobe. Among Echinopla, only E. striata was available for examination; the male of this species lacks 1m-cu, has a short third abdominal tergum, has a posteriorly-truncate head as in Polyrhachis, and is extremely hairy with both standing pilosity and pubescence. The male of Overbeckia has short scapes which are shorter than the head length, very close-set antennal toruli (separated by slightly more than one torular diameter), a small clypeus without an anterior lobe, and a long head posterior to the compound eyes.