Genera Insectorum: Emery's key to Camponotus subgenera of the New World

KEY TO THE SUBGENERA OF CAMPONOTUS FOR THE NEW WORLD

Below is Emery's (1925) key to the subgenera of Camponotus for the New World. Note the following: (1) hundreds of new species have been described since Genera Insectorum; (2) in some cases, there have been changes to the rank and limits of the subgenera, particularly splitting; and (3) the parenthetical numbers after the taxon names correspond to Emery's original ordination of the subgenera and their current ranks. What follows first is the leading text (translated) from Emery's original key.

"Given the large number of groups to be distinguished and the relative inconstancy of the characters on which they are established, I resolved to make two separate keys, one for the subgenera inhabiting the Old World and Australia, and the other for the American subgenera. The small groups, common to both hemispheres, are included in both keys.

In the Old World key, leads (= lugs) 10 and 16 may challenge the identifier, especially if only minor workers are available. Additionally, the subgenera which have numerous and highly variable species are interconnected by gradual transitions, such as Tanaemyrmex, Myrmophyma, Myrmamblys, and other small groups.

In the New World key, leads 7 and 13 are difficult, and the subgenera Tanaemyrmex, Camponotus, Myrmaphaenus, and Pseudocolobopsis on the one hand, and Myrmaphaenus and Myrmobrachys on the other, and have transitions from one group to another the other.

I confess that my keys are far from satisfying to me, and that I am afraid that beginning myrmecologists will be daunted by the considerable number of subgenera and by the various weaknesses of their diagnostic characters. The latter issue might have gained precision by increasing the number of subgeneric divisions, as previously mentioned. I did so when I found that certain species had exceptional characteristics, but within very restricted limits. It seemed to me, however, that by multiplying the subgenera beyond measure, the confusion was increased rather than diminished. To remedy this, I have, in some subgenera, established unnamed sections, either geographical or based on morphological characters which are more-or-less constant."

(Translated and edited by B. E. Boudinot, 14 February 2017.)

1

 * Tibiae large and strongly compressed, the metatibiae short, blade-like, tarsi flat; head not depressed ... 2
 * Tibiae not or somewhat compressed; when compressed, the head is very depressed (C. obtritus, Emery) (Plate 3, Fig 16, 16a) ... 3

2

 * Pronotum armed with an anterolateral (humeral) tooth on each side; dorsum of mesonotum through porpodeum produced as sharp, longitudinal ridge; metapleural spiracles visible from dorsal view on each side of the ridge; large species ... Myrmepomis, Forel (38. Subgenus)
 * Mesosoma without dorsal longitudinal ridge ... Myrmoplatypus, Santschi (37. Subgenus)

3

 * Mesonotum and propodeum fused, bearing a dorsal carina which bears two unpaired spines; spines present on petiolar scale (Plate 3, Figure 15) ... Myrmodirachis, Emery (35. Subgenus)
 * Mesosoma without medial carina ... 4

4

 * Antennae inserted remarkably distant from the clypeus, in the middle or even behind the middle of the frontal carinae; caste dimorphism very pronounced; in American species (truncatus group) there are no intermediaries between the majors and minors; the head of major workers is more-or-less cylindrical, and obliquely truncate anteriorly, with the truncated surface comprising only a part of the clypeus ... Colobopsis, Mayr (25. Genus [formerly subgenus])
 * Antennae generally inserted in anterior half of frontal carinae; the head of major workers not truncate, or if it is, the truncated surface generally includes all the clypeus ... 5

5

 * Head of majors strongly truncate; the truncated surface includes most of the anterior portion of the head up to the antennal insertions ... 6
 * Head of media, majors, and queens truncate or not; when truncate, the truncated surface does not include the anterior portion of the head up to the antennal insertions ... 7

6

 * Majors and queens with the truncate surface of the head in the form of a flattened or convex disc; a groove or scrobe along the front frontal serves to accommodate the base of the scape (Plate 3, Fig 10) ... Hypercolobopsis, Emery (30. Subgenus)
 * Truncated surface of the head formed otherwise; furrow along frontal carinae lacking ... Manniella, Wheeler (29. Subgenus)

7

 * In general, in small and medium-sized workers, the head is short, wider behind than before, with the posterior margin almost straight or slightly convex; eyes placed very posteriorly; caste dimorphism more or less pronounced: large workers or majors generally have short heads, with subparallel sides, rarely noticeably longer than wide; majors often with distinct sculpture (P1.3, Fig.9, 9a); mesosoma short and broad, sometimes impressed or incised dorsally anterior to propodeum ... 8
 * In general, among small and medium-sized workers, the head is longer than that of large or major workers, with parallel sides and narrower posteriorly (there are numerous exceptions to this rule, for example in the subgenera Myrmaphaenus, Pseudocolobopsis, etc.); ordinarily the eyes of the minor workers are not placed as posteriorly as above; caste dimorphism more or less pronounced; form of the head of the major workers or soldiers extremely varied in the different groups ... 10

8

 * Body flat, depressed; antennae and legs very long, tibiae compressed (Plate 3, Fig 16, 16a); color black; caste dimorphism poorly marked ... Myrmomalis, Forel (36. Subgenus)
 * With other character states ... 9

9

 * Dorsum of mesosoma bordered, propodeum also bordered and distinctly truncate posteriorly, with the dorsal face extending as a pair of flat teeth Myrmocladoecus, Wheeler (33. Subgenus)
 * Pronotum generally broad and flat, with a sharp lateral edge; propodeum narrow and with variable form, bearing in two species a small unpaired and bifurcating spine (Plate 3, Figure 14) ... Myrmeurynotus, Forel (34. Subgenus)
 * Mesosomal dorsum continuous or interrupted, rounded or subbordered; propodeum rarely subbordered; caste dimorphism sometimes very pronouced, often little marked ... Myrmobrachys, Forel (32. Subgenus)

10

 * Dorsum of mesosoma strongly impressed or incised anterior to propodeum; scapes and legs with fine, whitish setae; caste dimorphism pronounced ... Myrmosphincta, Forel (26. Subgenus)
 * Dorsum of mesosoma without impression, or when an impression is present, the scapes and tibiae without standing setae ... 11

11

 * In majors and females, the head is elongate, with sides more or less parallel, generally obliquely truncate anteriorly, posterior head margin straight or emarginate; mesosomal dorsum arched, continuous; most of cuticle shining ... Pseudocolobopsis, Emery (28. Subgenus)
 * With other character states: the head of the major worker, the soldier and the female are matte, at least when the sides of the head are parallel ... 12

12

 * Clypeus without an anterior lobe or rounded lobe, but anterior margin with a medial depression or notch; head wide among major workers; mesosomal dorsum, anterior to propodeum, impressed or not ... Myrmentoma, Forel (12. Subgenus)
 * Mesosomal dorsum continuous, without an impression anterior to the propodeum ... 13

13

 * The head of major workers, or of the soldiers and females in general, is about the same width anteriorly and posteriorly; anterior clypeal margin usually scalloped, or otherwise, in minor workers; scalloping along the anterior margin disappears as the head becomes larger; the malar areas sink and become prominent on the clypeus in major workers, thus some species have the convergent head shape of Colobopsis (C. salvini, Forel, silvestrii, Emery, etc.) ... Myrmaphaenus, Emery (27. Subgenus)
 * Head of workers and queens generally wider posteriorly than anteriorly; clypeus sometimes with an anterior lobe; lobe usually rectangular or rounded, persisting on workers of all sizes … 14

14

 * Head of minor worker rounded posteriorly (not conical); scapes and legs with bristly, standing setae ... Myrmothrix, Forel (7. Subgenus)
 * Scapes and legs with only appressed setae, otherwise the head of the minor worker is conical ... 15

15

 * Head of major workers somewhat broader posteriorly than anteriorly; head of minor worker rounded posteriorly; clypeus with or without a short anterior lobe ... Camponotus, Mayr (4. Subgenus)
 * Head of major workers generally wider posteriorly than anteriorly; head of minor workers variable among species groups; clypeus usually more or less carinate and with pronounced anterior lobe ... Tanaemyrmex, Ashmead (5. Subgenus)